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Playing with the Drake Equation

The BBC has put up an interactive web page with the parameters of the Drake equation that lets you tweak numbers and estimate how many alien civilizations might exist. It’s informative because you should quickly realize you can make up any old numbers you want for most of them — we simply don’t have data for most of them, so you have to reach up into your colon to pluck something random out.

They have various presets, including a modern “skeptical estimate”. I just looked at the section on life, and found it weirdly inconsistent. Apparently, the % chance a habitable planet develops life is guessed at 13% (I don’t buy it; that life arose so quickly on Earth after its formation suggests that it may be relatively easy — I’d jack that up to something high), while the % chance that life develops intelligence is pegged at an absurd 50%. We’ve got one planet with tens of millions of species for a data point, and our kind of intelligence popped up once in 4 billion years. It makes no sense to argue for that degree of inevitability for a weird and unlikely adaptation like intelligence…why didn’t it arise in the Mesozoic, then?

Their worst estimate (which looks ridiculously optimistic to me) ends up with only about one civilization per galaxy. That’s also with a conservative estimate that a civilization only spends about 400 years trying to send signals outwards…which would mean that a brief effort to talk to some other civilization within a disc 100,000 light years in diameter is almost certainly doomed to failure. Even in their most optimistic model, with tens of thousands of technological civilizations in a galaxy, stars populated by intelligent life are still about 600 light years apart.

At least the web page makes it obvious that the Drake Equation is like a Ouija board, with the tinkerers just pushing the numbers around until they get the answer they want.

Comments

  1. says

    There are two missing parts of the drake equation that once added make the rests of the equation much more realistic. If you have to multiply the equation by the probability of intelligent life on Earth. Then you have to divide by Jesus.

  2. charlessoto says

    Please no colon jokes. I have IBS and it’s no laughing matter. I understand it’s just your functional colon privilege talking, but please be sensitive.

    And who’s to say ancient reptiles didn’t have the Internets? Maybe that’s what killed them off…

    Yes, that’s a dumb web app.

  3. eric says

    That’s also with a conservative estimate that a civilization only spends about 400 years trying to send signals outwards

    I believe that particular value was originally supposed to represent the time in which a civilization would broadcast powerful, detectable radio signals (or other EM). We have been at it for about 100 years but I believe our broadcasts of that type are diminishing because of stuff like cable and improved antennae: we have found more efficient ways to do point-to-point signaling than just global shouting.

    So, IMO 400 years isn’t conseravative, its liberal. That assumes we will not find a more efficient way to talk to each other across distance in the next 300 years. A really conservative value would be about 150 years. That assumes that cheap physical connections (like cable), and extremely low wattage transmitters, and future solutions will completely eliminate the need for powerful broadcast radio signals in the next 50 years. Which they probably could.

  4. oolon says

    WTF, British Broadcasting Corporation… And I cannot access it from the bleedin’ UK!

    I can see it through avoidr.com, but is there meant to be some fancy javascript that lets me edit the values?

  5. coelsblog says

    I think it’s fun, totally pointless, but fun.

    It’s not totally pointless once you realise that it’s not supposed to give you an answer, it’s supposed to give you a road-map towards an answer. In the last decade or so we have made huge progress on the second and third terms of the equation (the fraction of those stars that have planets and the average number of planets that can potentially support life per star that has planets) when previously people would have regarded those as intractable. Who is to say how knowledge of the other terms might develop?

  6. sqlrob says

    It makes no sense to argue for that degree of inevitability for a weird and unlikely adaptation like intelligence…why didn’t it arise in the Mesozoic, then

    It did. They got wiped out in a nuclear war. Proven in this scientific simulation.

  7. nmcc says

    And to think, according to Bomber Harris in his Oxford lecture -with a doe-eyed Dawkins looking on – 30,000 children die of hunger or hunger related ailments every day of the week. But of course, scientists – as a bunch – have such lofty concerns! That’s what I like about scientists and their groupies, they spend such a reasonably proportionate amount of time trying to figure out really important issues.

  8. Enkidum says

    Yeah, I don’t get the hate for the Drake Equation. Provided you don’t think of it as actually providing a useful answer at the moment, but rather specifying what you would need to know in order to get one, and showing how those parameters would interact. It can be interpreted in pretty loony ways (“Hey guys, we have an x% chance of being contacted by intelligent life in the next 5 years!” or whatever) but there’s no need to do that.

    As coelsblog @7 says, we’ve made a huge amount of progress in recent years on two of the parameters, and it seems likely we’ll get further progress on some of the others in the decades to come. And maybe realize that we need to add other parameters or whatever. But the principle seems fine to me.

  9. CJO says

    the Drake Equation is like a Ouija board, with the tinkerers just pushing the numbers around until they get the answer they want.

    I suppose this is true, if there’s a particular answer one wants, or if one expects an authoritative answer at all. But if all you’re looking for is a thought experiment that subjects our ignorance on these matters to some parameters, I think the DE is interesting to bat around.

    eric:
    400 years isn’t conseravative, its liberal.

    Yes, and not just for the reasons you say. It also assumes that the side-effects of ramping up to a technological, EM-emitting, planetary-scale civilization don’t tend to be the very factors that doom it to catastrophe in a shorter period on average than 400 years. The way the next few decades are likely to go here on Earth, I wouldn’t give us that great of odds to still be a technological, EM-emitting, planetary-scale civilization in 2100.

  10. says

    nmcc blathered:

    And to think, according to Bomber Harris in his Oxford lecture -with a doe-eyed Dawkins looking on – 30,000 children die of hunger or hunger related ailments every day of the week. But of course, scientists – as a bunch – have such lofty concerns! That’s what I like about scientists and their groupies, they spend such a reasonably proportionate amount of time trying to figure out really important issues.

    And here you are, demonstrating your profound love of starving children, by trolling on a biology professor’s blog.

    Why are you wasting your time here, rather than doing something truly world-changing, such as donating your major organs to orphaned children in third-world countries?

    Cheers,

    b&

  11. says

    F wrote:

    ###-divide by jesus error-

    Well, we’ve had so many conquer by Jesus errors, it only makes sense we should have some divide by Jesus errors as well….

    b&

  12. says

    I’d look at the Drake equation like a spreadsheet, where you can go ahead and calculate the results of various numbers. Of minor use, but not of no use.

    Unless Chopra gives us the numbers, then we should know how common life is in our universe.

    Glen Davidson

  13. says

    Ben Goren

    Well, we’ve had so many conquer by Jesus errors, it only makes sense we should have some divide by Jesus errors as well….

    Bwahahahaha! Both happen because people decide, when programming reality, that their kludgy solution is “good enough”.

  14. slowdjinn says

    nmcc – Worldwide, there is no shortage of food, there is also no technical problem with transporting food from areas of surplus to areas of deficit.

    Those 30,000 deaths are a political problem, not a scientific one.

  15. Brain Hertz says

    I believe that particular value was originally supposed to represent the time in which a civilization would broadcast powerful, detectable radio signals (or other EM). We have been at it for about 100 years but I believe our broadcasts of that type are diminishing because of stuff like cable and improved antennae: we have found more efficient ways to do point-to-point signaling than just global shouting.

    Actually, I don’t think that really works. Having gone over the numbers for a link budget for detecting alien civilizations, I just don’t think there’s any way that we could detect radio emissions that were unintentional; what we’d need to look for is an intentionally transmitted and highly directional signal, directly beamed at us.

    This seems to be a common point of confusion, and I asked Seth Shostak about it a couple of years back. He confirmed that the assumptions of the SETI Institute require that we’re looking for an intentional signal.

  16. johnbebbington says

    PZ wrote: “Their worst estimate (which looks ridiculously optimistic to me) ends up with only about one civilization per galaxy”

    Is it possible to have more than one intelligent species competing with each other on the same planet? On Earth, it’s bad enough having different tribes/nations/religions/politics fighting each other without having horses/dogs/republicans setting up their own civilisations and stealing our valuable resources.

  17. raffles says

    Dr. Myers (or anyone that knows),

    You mention only one intelligent form of life evolving on Earth, but I was curious, did Neanderthals evolve intelligence separately from Homo Sapiens or was it already developed (or developing) prior to speciation? Were we even entirely separate species by they time Neanderthals disappeared or is that still a topic being debated?

  18. says

    >>We’ve got one planet with tens of millions of species for a data point, and our kind of intelligence popped up once in 4 billion years. It makes no sense to argue for that degree of inevitability for a weird and unlikely adaptation like intelligence…why didn’t it arise in the Mesozoic, then?<<

    This then raises the annoying question of what we mean by "intelligence". Drake's original definition was pragmatic – "able to build a radio transmitter that can be detected over interstellar distances" (which would make f_c redundant, since it's equal to one).

    On the other hand, I've heard arguments that intelligence has arisen at least three times on Earth – that was based on counting all animals with more than some arbitrary number of synapses and observing that mammals, birds, and some cephalopods have evolved that amount of brainpower independently. Are cuttlefish smart enough to be called intelligent, even if they aren’t going to build radios anytime soon?

    But you’re quite correct that the Drake equation is easy to over-interpret. It’s useful as a way to break apart the problem of looking for aliens, nothing more. As others have noted, thanks to the Kepler mission we now know the fraction of stars with planets and can even begin to constrain the number of planets that are habitable (whatever that means). If we fly something like the proposed New Worlds Observer (http://en.wikipedia.org/wiki/New_Worlds_Mission), in twenty years we will at least be able to set strict limits on the fraction of planets with abundant life.

  19. says

    I’ve always felt that the Drake equation is more of a parlor game than anything else–all it takes is one bottleneck we haven’t thought of, and the whole thing sort of takes a dump. A long time ago I read an article that posited that without the little nematodes that create lodestone, early scientific-types would not have had naturally occurring magnets to experiment with and we might not have developed our technological civilization so fast, if ever.
    I’m not going to vouch for the truth content in that, though.
    One bit of possible usefulness, though–it’s easy to come away with the idea that life, and maybe even intelligent life, can be ridiculously improbable and still happen at least once in the universe.

    But of course, scientists – as a bunch – have such lofty concerns! That’s what I like about scientists and their groupies, they spend such a reasonably proportionate amount of time trying to figure out really important issues.

    Yeah, like this useless poindexter dude. Norman Borlaug

  20. nowimnothing says

    @johnbebbington

    On the conservative side you could say we definitely competed with Neanderthals as well as a few other intelligent hominids.

    On the more liberal side you could say we are still competing (and winning!) against intelligent apes and cetaceans.

    On a more serious note, just like the drake equation does show us how big space and time are, the likelihood of two intelligent species that are not closely related being at a very equal population size, technological development, etc. at the same time is pretty small. So for most intents and purposes it is likely that it would be a very unequal competition.

  21. says

    There’s another useful exercise with the Drake equation:

    Given any estimate of the number of transmitting civilizations currently in the galaxy, we can work out how far away the nearest is (assuming a uniform distribution). That tells us how long it takes a message from them to reach us and vice versa. Unless you make the timespan of a civilization very long, by the time you receive a signal from ET, that civilization is already gone. Just as an example, if N = 30,000 for the Milky Way, the nearest aliens are ~1000 lightyears away, so you’re listening to dead cultures unless L >= 2000 years. Even if there were some cultural continuity, it would be like me getting a 10th century commentary on Sun Tzu.

    And the time lag gets longer and longer for smaller N. In this regime, it goes as 1/N^2 with decreasing N, until N = 1 – then it jumps up as we go to intergalactic distances. For N > ~100,000, it goes as 1/N^3, because the distance to the aliens is comparable to or less than the thickness of the galactic plane.

    In other words: SETI isn’t talking to aliens. It’s archaeology.

  22. gillt says

    It makes no sense to argue for that degree of inevitability for a weird and unlikely adaptation like intelligence

    Then maybe intelligence was not an adaptation but a random event or series in the human lineage. Isn’t that the null hypothesis anyway?

  23. eric says

    Brian Hertz @19:

    This seems to be a common point of confusion, and I asked Seth Shostak about it a couple of years back. He confirmed that the assumptions of the SETI Institute require that we’re looking for an intentional signal.

    Thanks for the correction, but…

    (1) Is ‘what SETI is looking for now’ really the same thing as ‘what L represents in the Drake Equation’?

    (2) If the answer to (1) is “yes,” then doesn’t that mean our civilization has been doing it for 0 years? This would make the 400 year estimate even more liberal than it is under my interpretation. It would also make L a political or cultural factor rather than a technological capability factor, because with intentional targeted signaling they have to be motivated to contact aliens. And not just aliens, but us specifically.* With broadcast radio, you just have to assume they use it for themselves.

    *Doesn’t this make it a really silly factor? Literally, trying to estimate how long aliens from an undetermined location decide to beam something at the Sol system.

  24. elvenpiratefish says

    @20

    It’s generally assumed that human style, tool using intelligence is a very specific niche. It’s highly unlikely that, even if two such species developed on a planet, they would not compete and one would eventually wipe out the other. Look at how the different hominids competed with each other through pre-history. For a good, though obviously not perfect example, just consider how much we compete intraspecifically, creating artificial classifications such as race to justify one groups superiority over the other.

  25. says

    @Brain Hertz:

    It’s a bit more complicated than that. The radio leakage from TV transmitters on Earth is basically omnidirectional, and could be detected by a square kilometer of radio antenna up to ~50 lightyears out. Military and astronomical radars are far more powerful and can be detected at distances up to a thousand times further away, but they are directional and transient. On the net, the radar leakage detectable by a given antenna over about 30 times the volume of the TV leakage. Reference (and self-promotion): http://arxiv.org/abs/1207.5540

    It would be relatively easy to build a radio beacon that was far more detectable than even the radar leakage, but no one on Earth has done that yet (I could arrange such a project if given 10 million USD). SETI works on the assumption that we will most likely detect either a dedicated beacon or a radar that somebody was using thousands of years ago.

    @raffles:

    According to the gene sequencing work, we never fully speciated from neanderthalensis, so it’s not accurate to say that we evolved intelligence separately from them.

    In comparing our ancestors to the other ape lineages (chimp, gorilla, orang), the question becomes what we count as “intelligence”. If you require the set of cultural traits called “behavioral modernity”, then we evolved intelligence within the last hundred thousand years (give or take quite a bit) and intelligence apparently evolved only once on Earth. If you define intelligence as say “able to pass the mirror test”, then it evolved along the ape lineage many millions of years ago and has evolved separately on other lineages.

  26. woodsong says

    eric, IANAA, but I think the types of signals that SETI could pick up would include our Deep Space Network signals to probes like Cassini–if Saturn (from Earth’s viewpoint) passed in front of a star that hosted intelligent life, there’s a chance that that civilization might pick up our commands to Cassini.

    Some alien cephalopods might pick up a few days of space-probe command sequences in a thousand years or so. Who knows what they’d make of that, or whether they would want to reply?

    Trying to reply to a thousand-year-old signal could be an interesting exercise, givan stellar motions…

  27. marcus says

    “…and our kind of intelligence popped up once in 4 billion years.”
    We actually don’t know how many time “our” kind of intelligence has “popped” up. We don’t know what type of intelligence the Neanderthals had, for example. We just know that we’re only one with our kind of intelligence that has managed to survive.

  28. says

    @eric @27:

    SETI is looking for any radio (or in some cases optical or near-infrared) transmission produced by an extraterrestrial intelligence. It happens that radar leakage or a dedicated beacon would be far easier to detect than the more diffuse leakage from, e.g. a television station.

    Drake’s original definition was defined irrespective of the transmit power, bandwidth, or directionality of ET’s radio transmitter – it was “build and use a radio at a frequency that can be detected over interstellar distances”. By that definition, L for humanity is ~80 years – earlier lower-frequency transmitters didn’t escape through the ionosphere. If you say “be as detectable as humanity is right now”, then L is ~40 years (the Arecibo radar transmitter was installed in the early ’70s).

  29. says

    @woodsong:

    Stellar motions can be tracked reliably enough for hundreds of thousands of years that aiming a reply isn’t a problem. Having someone there to listen to you is.

    Also: Deep Space Network uplink telecom is more detectable than the omnidirectional leakage, but far less detectable than Doppler radar transmissions. The uplinked commands impose a bandwidth on the signal, which make it harder to detect. The best detectability ends up being signals with ~0.1 Hz bandwidth (the Earth’s rotation smears out narrower transmissions). It takes a long time to say anything with a SETI beacon, but if you have a thousand years to say it, you can be patient.

    @marcus:

    Again, we _are_ descended from neanderthalensis.

    Also, we can be quite sure that no civilization at all like ours has been present on Earth before. Even absent fossils or ruins (the Apollo sites will be recognizable for tens of millions of years), there would be geochemical evidence – we’ve put oddball long-halflife radioactives into the environment as a result of our playing around with nuclear power.

  30. Nightjar says

    Homo Sapiens

    Homo sapiens.

    We actually don’t know how many time “our” kind of intelligence has “popped” up. We don’t know what type of intelligence the Neanderthals had, for example.

    I wouldn’t say Neanderthals and humans represent two separate instances of intelligence “popping” up. Really, we’re so close that for this purpose I would include them in “us”, if you know what I mean.

  31. says

    @myself @34:

    Checking the current impact rate on the Moon (measured in the 1970s by the Apollo seismic network), I find that I underestimated the lifetime of the landers by an order of magnitude. They will be recognizable for _hundreds_ of millions of years. On a billion-year timescale, they’ll get eroded by micrometeorite hits and possibly buried in ejecta from other impacts and will no longer be readily distinguished from the residue of nickel-iron meteorites hitting the surface.

    But we can quite definitely say that we are the only species in the history of the Earth to land on the Moon.

  32. elvenpiratefish says

    I think several are you are looking at it wrong; modern human intelligence is not a “pop” and it’s here phenomenon. It’s a gradual process of selection over millions of years. Our archaeological and paleontological research indicate only one lineage having developed tool using intelligence as a survival strategy, the hominids. Splitting the different hominid species up to figure out how many intelligent species there have been is splitting hairs and making this a needlessly complex arguement.

    PZ has it right, the question is not how many tool using intelligent species have there been, it’s how many lineages. So really, the question at the heart of the drake equation is what percentage of planets with life develop such a lineage. Some (including PZ) argue that the number of mass extinctions on earth would say the odds are low. Others, myself included, would say that since none of those mass extinctions ever completely wiped out all life on earth you can’t make that arguement and the answer is unknown till we find other planets with multicellular life. The problem is that, we don’t know what the minimum level of complexity is for our kind of intelligence to exist (for example the End Ordovician event happened 30 to 40 million years before life had moved out of the ocean). If intelligent life happened at the earliest point in our planetary development possible then you are talking very strict requirements for it to appear (terrestrial, endothermic,omnivorous, highly segregated organs etc.)

  33. says

    Weren’t there dinosaurs that were looking to be pretty smart before they got wiped out. Could it be the major extinction events caused it to take 4 billion years for technological life to develop.

  34. marcus says

    I will specify that neanderthals are “us”. I was describing “our kind” of intelligence as self-aware and highly conscious (whether terrestrial, endothermic,omnivorous, highly segregated organs or not.)
    (/)Pedant
    We can not say that we “know” that this type of mind has not existed at some point or might not exist still.

  35. DLC says

    About intelligence : it kind of depends on how you define intelligent life, but let’s assume that for our purposes, intelligent life is that which has or is capable of creating equipment that can disturb the electromagnetic spectrum enough to be noticed by mechanical receptors elsewhere. If we limit ourselves to that, then the Dolphins are out. as are whales, dogs, chimps and other non-human primates. Although, some species of primate do use tools, they don’t build generators or radio towers. Could a species evolve which was directly able to influence electromagnetic without machines ? It’s useless to speculate. Amusing perhaps, in moments of idleness such as this, but useless.

  36. elvenpiratefish says

    @computerguy

    That all depends on what the requirements are for intelligence to develop. Extinction events, while bad for diversity also tend to lead to big speciation events as niche’s suddenly open up that were filled previously. Look at the KT extinction event; which allowed mammals to rise to their current terrestrial prominance. It’s possible that without some of those extinction events this planet would still be dominated by single celled organisms.

  37. elvenpiratefish says

    @Marcus

    You’re right, we don’t know whether such tool using intelligence as ours as existed in other lineages besides our own (I mean tool using in that tool use is something we are dependent on, chimps use tools but they are not dependent on them for their survival, humans as a whole are.) However, we have no evidence that such a lineage has ever evolved seperately on Earth. Until we do, and without any reason to believe that it has, the proper assumption is that ours is the only such lineage to have evolved on Earth. The question then becomes, which traits of Homo Sapien are prerequisites for that kind of intelligence and which ones just happen to be there. On one end of the spectrum you could assume that several of our traits are prerequisites for intelligence, on the other you can assume that almost none are (though that seems unlikely as you would then expect to see evidence of intelligent life earlier in the planets history).

  38. opposablethumbs says

    Does anyone know a way to see an interactive version of the page from the UK? (avoidr.com shows a non-interactive page, as oolon says in #5) It would be fun to play with it …

  39. dysomniak, darwinian socialist says

    Weren’t there dinosaurs that were looking to be pretty smart before they got wiped out. Could it be the major extinction events caused it to take 4 billion years for technological life to develop.

    Assuming you’re correct and dinosaurs were on track to start building radios before the KT event that certainly would change things. If things had happened that way it might have only taken 3.95 billion years!

  40. says

    I do have a question. I thought I read somewhere that life on earth took over two billions years just to advance beyond single-celled organisms. Is there some sort of “evolutionary hurdle” that a planet would have to overcome before more complex life starts showing up?

    Or am I totally off-base in the first place? And if I said I was really interested in how we moved from bacterial/single-celled life to multicellular life, what would be some good entry-level books to read?

  41. mrheteronormative says

    Dr. Myers, I think you made a mistake here. You seem to have accidentally made a post dealing with a skeptical/scientific issue.. Surely there is a female blogger out there who got a demeaning comment on her blog post and thus proves the nationwide male hegemony that is to be warred against at all costs?! Seriously now, get back on topic.

  42. says

    Surely there is a female blogger out there who got a demeaning comment on her blog post and thus proves the nationwide male hegemony that is to be warred against at all costs?!

    If not, I’m sure you can provide one, jerk.

  43. says

    This was my take from an old lecture. Tried to base the issues of evolution, evolution of intelligence, and duration of technological civilizations on realistic natural historical values.

  44. woodsong says

    michaelbusch, I hadn’t realized that DSN signals were less clear than other existing signals we’re putting out–I’ve heard of doppler radar, but wasn’t thinking of it!

    I have to admit, my curiosity is piqued: How far out could an alien civilization be, assuming the abovementioned 1 km2 radio receiver, and still pick up, say, the Mars rovers’ wake-up music? How many hours or days, at that range, would the alingment of Earth-Mars-exoplanet last, assuming optimal geometry?

    Nathaniel Frein, one limitation on early Earth evolution was the atmospheric oxygen level. Before 2.4 billion years ago the O2 level wasn’t significant, so multicellularity (and possibly eukaryotes) couldn’t evolve. This was about 1.1 billion years after the earliest known bacterial life appeared, at least as far as we know (Source: Wiki’s article on “Atmospheric Oxygenation Event”).

  45. says

    raffles: Intelligence in Homo is a single instance; we and Neanderthals were two expressions of the same evolutionary event.

    Nathaniel Frein: the causes of the origin of multicellularity is a hotly debated topic. A fairly good review is:
    Grosberg, R.K. & R.R. Strathmann. 2007. The evolution of multicellularity: a minor major transition? Annual Review of Ecology, Evolution, and Systematics 38:621-654.

    Also, although multicellularity is not one of the specific “ten great inventions”, it is covered to some degree in:
    Lane, N. 2009.
    Life Ascending: The Ten Great Inventions of Evolution. W.W. Norton. 352 pp.

  46. Amphiox says

    It makes no sense to argue for that degree of inevitability for a weird and unlikely adaptation like intelligence…why didn’t it arise in the Mesozoic

    During the mesozoic, at least as far as we have fossils for, the species with the highest EQs were far, far below the threshold that would be expected to be likely to generate technological intelligence.

    However, the average EQ of the very smartest lineages at the end of the Mesozoic was higher than at the middle, which was higher than the beginning, which was higher than during the Permian, which was higher than in the Carboniferous, and so forth all the way back to the beginning of brains.

    And after the mesozoic, the average EQ of the smartest lineages in the early Cenozoic were greater than those of the late Mesozoic, and those of the middle Cenozoic greater still, and even greater in the late Cenozoic.

    There actually HAS been a rough trend over the course of multicellular animal life on earth for the species with the greatest intelligence to get progressively smarter.

    So I most definitely do not think that a statistical argument using earth as the only example of a biosphere (ie 1 technological species out of however many trillions there have been on earth) is actually valid for arguing that intelligence should be rare. The reason being that the denominators are different. What if EVERY habitable planet always generates trillions and trillions of species (a conjecture that is not far-fetched)? Then, even if the odds of any particular species evolving intelligence is only 1 in a trillion, the odds of at least one species eventually evolving intelligence during the habitable lifespan of a habitable planet will rapidly approach unity.

    And the trend I describe above can be easily interpreted as suggesting that it simply takes 3.8 billion or so years for all the preadaptions necessary for technological intelligence to appear to first evolve, and that technological intelligence on earth was not in fact possible until very recently.

    And until we find a second habitable biosphere to compare to Earth, we can’t distinguish easily between these two arguments.

    Weren’t there dinosaurs that were looking to be pretty smart before they got wiped out. Could it be the major extinction events caused it to take 4 billion years for technological life to develop.

    The most intelligent dinosaurs at the end of the Mesozoic were the Troodontids. They were even smarter than the late Mesozoic mammals. (At least the ones we know about).

    Their EQs were roughly equivalent to that of a modern domestic chicken – ie in the “dumb” range for modern birds. Mesozoic mammals were even slightly worse.

    In other words, the dinosaur lineage got, on average, steadily smarter throughout the Mesozoic, and continued to get even smarter (as birds) over the course of the Cenozoic. The mammals did too, and the smartest known members of both those clades appeared in modern or near-modern times.

    The same, in fact, is roughly true for cephalopods, too (ancient ammonites and nautiloids were dumb compared to modern cephalopods), though our fossil record of their brains much more patchy.

    Are cuttlefish smart enough to be called intelligent, even if they aren’t going to build radios anytime soon

    Sure, if by soon you mean a couple thousand years. But if by soon you mean 20 million years, well, compare cuttlefish behavior today with the hypothesized behavior of our own primate ancestors from 20 million years ago…. (Of course we humans would have to vacate the niche first before they’d have a chance to evolve into it….)

    But we can quite definitely say that we are the only species in the history of the Earth to land on the Moon.

    Actually we can’t. We may be able to say we’re the only ones to deliberately launch for and succeed in landing on the moon.

    http://en.wikipedia.org/wiki/Reports_of_Streptococcus_mitis_on_the_moon

    And if it could happen this way, it can also happen with non-deliberate meteroid transfer.

    Our archaeological and paleontological research indicate only one lineage having developed tool using intelligence as a survival strategy, the hominids.

    Are you including Chimpanzees, Orangutans, and Gorillas as hominids?

    Even if you don’t, there are also cephalopods (both Cuttlefish and Octopuses, so 2 lineages there), Corvids and Parrots (2 more), Cetaceans, and Elephantids.

  47. woodsong says

    Thomas Holtz, I’ll have to read that at my leisure–it looks interesting. IANAB, but I do have a lot of curiosity! Thanks!

  48. robro says

    It makes no sense to argue for that degree of inevitability for a weird and unlikely adaptation like intelligence…why didn’t it arise in the Mesozoic, then?

    So when does this intelligence business take place? Are we expecting it soon? The signs are blurry at the moment.

  49. robro says

    Ferƒalboy12:

    all it takes is one bottleneck we haven’t thought of, and the whole thing sort of takes a dump.

    Yes indeedie, there are many unknown unknowns in this equation, but that’s well known. I once had the thought: What if there were no birds? What might humans have missed? We take them so much for granted, but perhaps one passing overhead caused someone to look up and really notice the sky or clouds or stars.

    Still, it’s fun to pretend we can calculate the number of worlds and civilizations and so forth. Some day a long time from now we might get to a reasonable approximation.

  50. says

    @woodsong @50:

    We use the Deep Space Network 70-m antenna at Goldstone for Doppler radar as well as for telecom. It’s detectable over about 10% the volume and a little less than half the distance of the Arecibo Planetary Radar (given an equal collecting area for receive).

    The rover wake-up music is not transmitted to Mars – it’s for the operators’ enjoyment, and it would be a waste of bits. Bandwidth from Earth to rover direct is 100-1000 Hz (the high-gain antennas on the orbiters can do a bit better), which would be detectable by a square kilometer array at between 3000 and 1000 lightyears.

    Mars moves between ~0.2º and ~0.75º per day relative to the stars as seen from Earth, and the Goldstone 70-m beam is ~0.03º wide, so any individual star can only see the beam for between 1 and 3 hours at most, potentially with a gap as Mars blocks the beam from the star.

    @Amphiox @54:

    The microbes wouldn’t have gotten to the Moon on their own (meteorites ejected from the Earth are heat-sterilized), so the point is moot.

  51. Amphiox says

    michaelbusch @58;

    Are you absolutely certain that all such ejecta would always be heat sterilized all the way through, even to the deepest interior parts of the rock? All the time? Because it doesn’t take that high an exception rate to make the transfer possible, or even likely, to have occurred at least one time.

  52. elvenpiratefish says

    “Are you including Chimpanzees, Orangutans, and Gorillas as hominids?

    Even if you don’t, there are also cephalopods (both Cuttlefish and Octopuses, so 2 lineages there), Corvids and Parrots (2 more), Cetaceans, and Elephantids.”

    I did mention as primary strategy. All of the above can use tools to one degree or another, but none of them are dependent on them as the hominids are and none of them demonstrate the tendency for the significantly more advanced parts of tool use such as using a tool to make a tool. Cephalopod tool use for example is limited to the most basic form on par with that of a hermid crab, which is far different from crafting a stone hand axe or making a spear.

  53. Amphiox says

    Note that random broadband broadcasts dissipate to be indistinguishable from background radiation within a few light years. A detectable signal actually has to be a focused aimed beam. So aliens, unless they have detection capabilities beyond anything we can even dream of, will not be watching I Love Lucy.

    So the time number for detectability isn’t going to be the time they are using broadband radio producing leakage we can pick up, it is the time they are likely to have the resources, desire, and political will to maintain a focused continuous signal transmission of rather substantial power. Taken in that light, even 50 years might be an optimistic estimate. (How many large scale expensive science projects have we humans managed to continue for more than a decade or two?)

    However, length of detectability also depends on our own technology. If we figure out how to detect signs of intelligence other than radio waves, the detection window could expand enormously.

    If, for example, we develop the ability to resolve exoplanet surfaces in telescopes with sufficient power to identify city lights on the night side, we could be looking at a detection window of thousands of years. If we could image the controlled use of fire, that could make it a million years or more.

  54. Amphiox says

    elvenpiratefish, IIRC, corvids have been observed to use tools to make tools. And remember that our own lineage must have started with such rudimentary tool use and expanded it from there. And so long as we exist, we actually inhibit the development of tool use in other species through niche exclusion. If we went away, how quickly might extended tool using intelligence re-evolve on earth?

    The point being that the immediate evolutionary precursor to our type of extended tool use evolved independently several times, and simultaneously in the modern era. Once we appeared we skewed the selective pressures by our very presence (once humans appear, evolving tool use for any other species has the detrimental effect of putting them in competition with humans). It doesn’t really take much, evolutionary speaking, to go from capable of using tools some of the time to using tools most of the time to completely dependent on tool use for survival. But the very first lineage to achieve technological intelligence will likely abort its development in all other insipient tool users, unless there are enough geographic barriers to prevent the first tool user from spreading thought the planet.

  55. wholething says

    Some versions use the age of the galaxy but I think you have to discount the first 5 to 10 billion years because the early galaxy would only have hydrogen and helium.

    Our planet seems to have developed life almost as soon as the galaxy developed the chemistry and planets with that chemistry to support life.

  56. jasonnishiyama says

    I think the key thing to remember about the Drake equation is that it was developed to start the conversation for the 1961 SETI conference. It’s original intent wasn’t to work out an actual number, just to start the conversation on what do we need to know.

  57. says

    @Amphiox

    @59:

    An impact that ejects material from the Earth runs rocks through >10 km/s of velocity change by applying an impulsive velocity change. This shock-heats the rocks.

    For martian meteorites, which go through half the velocity change, the shock heating is >>10 C, with a limit of ~1000 C (higher heating starts to vaporize the rocks). Reference: http://onlinelibrary.wiley.com/doi/10.1111/j.1945-5100.2005.tb00409.x/abstract . For ejecta from the Earth, the minimum shock heating is >>40 C and most material is heated by hundreds of C. It’s pretty well baked.

    @61:

    You’re correct that broadband signals become indistinguishable from noise at relatively small distances. But you are not correct that a detectable signal has to be a deliberately aimed beam.

    The carrier waves of TV transmitters cover all of space with a complex pattern of narrow-bandwidth spikes and, as I said, are detectable by a square kilometer of collector up to ~50 lightyears away. Radar beams are transient in any one place, but the military radars cover at least the entire northern hemisphere quite often. Arecibo has covered a small fraction of the sky, but is still detectable over a huge volume – the beams are cones with narrow opening angles, but they are very very long.

    One good design for a dedicated SETI beacon would be a fan beam, which transmits in over half of a great circle around the sky. Put such a thing near the equator and align it north-south, and it will transmit to every point in the universe once per day. Of course, there still has to be a watcher out there to see it. And, conversely, there has to have been such a thing built by some aliens close enough for us to detect it.

  58. consciousness razor says

    Some versions use the age of the galaxy but I think you have to discount the first 5 to 10 billion years because the early galaxy would only have hydrogen and helium.

    Err, the first stars existed a few hundred millions years after the big bang, and I’m pretty sure most of those were giants, so they only lasted for some millions of years. So I think we could safely say there was only hydrogen and helium (and lithium) for the first billion years, give or take.

  59. elvenpiratefish says

    Amphiox, valid point; although the alternate hypothesis would be that while very basic tool use may be common, the movement towards more advanced tool use requires very specific evolutionary pressures. It seems rather odd to me that, save the primates, the examples you gave have been around far longer then our own and yet never moved beyond the most basic tool use. The corvidae, for example, are roughly the same age as the great apes yet there is no evidence of them ever having moved beyond the most basic tool use. The question we have to ask is why?

    But regardless, lets say that there are four families (the corvidae, the elephantidae, the hominidae, and the octopodidae), out of the millions that have existed in Earth’s history, that have developed basic tool use, one of which eventually produced a sub-family that moved to advanced tool use. That still makes the use of tools a very rare adaptation; and given the fact that half of those families have been at it significantly longer then us (the octopods have been around 95 million years or so) and never got beyond picking up shells to use would seem to support the idea that there are some very specific selective pressures needed to select for advanced intelligence and tool use.

  60. woodsong says

    michaelbusch @58:

    The rover wake-up music is not transmitted to Mars – it’s for the operators’ enjoyment, and it would be a waste of bits.

    Okay, that wasn’t clear from the press releases I read at the beginning of the Spirit and Opportunity missions–whether it was the intended implication or not, I thought it was being transmitted! It does make more sense to conserve bits, and keep the music for the operators, although I was enjoying the thought of aliens doing a Contact-style communication with rover music! Thanks for the clarification.

    Mars moves between ~0.2º and ~0.75º per day relative to the stars as seen from Earth, and the Goldstone 70-m beam is ~0.03º wide, so any individual star can only see the beam for between 1 and 3 hours at most, potentially with a gap as Mars blocks the beam from the star.

    So a civilization in the beam wouldn’t be likely to pick up a repeat signal, which IIRC is one of SETI’s criteria. I’m assuming that orbital inclinations are such that its unlikely for a probe to line up with the same star twice.

    Thanks for indulging my curiosity!

  61. says

    @woodsong @68:

    Deep-space telecom and radar beams aren’t likely to line up frequently with many stars, but the much-weaker TV carrier waves do. This is reflected in the strategies used by SETI@home and the Allen Telescope Array: they look for narrow-band transient radio signals, sieve out those attributable to RFI, then re-visit the remaining locations with much higher sensitivity, looking for any other signals. So far, they have found nothing, which rules out an Earth-like pattern of radio leakage around the nearest few stars and high-power dedicated beacons out to a much larger radius (we do not yet have a square kilometer array, so the limit on picking up Earth-like leakage is lower than the numbers I gave above).

    And thanks for your interest in radio astronomy!

  62. Amphiox says

    But regardless, lets say that there are four families (the corvidae, the elephantidae, the hominidae, and the octopodidae), out of the millions that have existed in Earth’s history, that have developed basic tool use, one of which eventually produced a sub-family that moved to advanced tool use. That still makes the use of tools a very rare adaptation;

    Rare by what standard? (Rare is a comparative term). As I have pointed out before, no matter how rare any specific adaption is on earth that rarity actually says zero informative about how likely we are to find another example on another planet.

    Because what we learn on earth is the rarity of the adaption per species on earth. What we need to know to answer the likelihood of finding that adaption in space is its rarity per planet at the time we are capable of searching for it. So we know an adaption arises once per trillion species on earth. How do we translate that to frequency per habitable planet? We would need to know the average number of species that an average habitable planet produces.

    We don’t know that. And depending on what that number turns out to be, our observation of 1/ x trillions on earth can translate to ANYTHING between infinitesimally above 0 and approaching 100% for the likelihood of finding that adaption on another planet.

    and given the fact that half of those families have been at it significantly longer then us (the octopods have been around 95 million years or so) and never got beyond picking up shells to use

    What do we know about the brains of those “octopods” from 95 million years ago? Were they already similar in size and sophistication to modern octopuses and cuttlefish? When, precisely, did the cephalopods start evolving the sophisticated brains we observe today?

    Do we actually know?

    When you think about it, in terms of evolutionary time, the clade of cephalopods is more directly analogous to the entire clade of vertebrates, which makes the clade of octopods far more directly analogous to the entire clade of mammals rather than the clade of just primates. So what were the mammals doing tool-wise 95 million years ago?

    would seem to support the idea that there are some very specific selective pressures needed to select for advanced intelligence and tool use.

    We have tried to explore what these selective pressures are, in our studies of our own origins, and so far we have not been able to think of a single plausible example of such a pressure that isn’t flat-obvious routine, rather than specific or special.

    But suppose it is specific. How specific? Specific to earth? But how does that translate to specific for habitable planets in general?

    Suppose it is so specific that it only arises a few times every 4 billion years on earth. How does that translate to how specific it will be for habitable planets in general. Well to answer that question we need to know how long habitable planets stay habitable on average. And we don’t know that. At any rate there are lots of stars (K class and below) that will live much longer than our sun, while still being able to host sizeable habitable zones that will remain habitable far longer than the habitable zone our earth currently enjoys. And these stars are even more common in the universe than sun-like stars. So how likely will such “rare” circumstances arise on a habitable planet that is already 6 billion years old? 8 billion? (As others have pointed out earlier, it is unlikely that any habitable planet in the universe will be much older than 8-10 billion years, though, due to the decrease in metallicity as we go back in time to earlier in the universe’s evolution).

  63. Amphiox says

    Remember that, until we actually find other habitable planets and can make direct comparisons, the null hypothesis for a habitable planet will be that this planet will have a habitable history that will span billions of years, like earth, and will support trillions if not quadrillions of species over its habitable lifespan, like earth, and will be subject to constantly changing climactic conditions, driven by plate tectonics, like earth, changes in stellar heating, like earth, and random impacts, like earth, among many other factors.

    Such a planet will be host to a vast variety of environments, with land of all elevations and water of all depths, temperature gradients from freezing to tropical, just like earth.

    So how frequently we observe something happen on earth can tell us absolutely nothing certain about how likely we are to find a similar thing on another planet until we know how typical, or atypical, earth is within the spectrum of all habitable planets. Until that time, you can take your data on earth and make whatever statistical or likelihood hypotheses from it, ranging from zero to 100%, and ALL are equally valid (or invalid).

    Until we find at least one other habitable world to compare earth to.

  64. lpetrich says

    I will concede that the Drake Equation is oversimplified, but it’s a good breakdown of the overall problem. Half a century later, we can get a handle on at least some of it.

    R* – star formation – well-understood

    fp, ne – frequency of planets and number of habitable ones. We are detecting numerous extrasolar planets, though many of them are “hot Jupiters”, something that nobody had predicted. We have also observed numerous protoplanetary nebulae,

    fl – we are a bit closer, with the help of extrapolating evolution backward. So far, the earliest stage that we can reconstruct with any confidence is the RNA world, and we have an idea of how DNA and proteins emerged from that.

    Proteins were originally coenzymes that got elaborated on until they became the primary enzymes. Ribosomes’ most important parts are their RNA’s, and they work with transfer RNA’s and messenger RNA’s to assemble proteins. BTW, several coenzymes likely go back to the RNA world, like ATP and niacin and thiamine and flavins and coenzyme A and porphyrins.

    DNA is essentially modified RNA; its building blocks are made from RNA ones.

    The main criticism of the RNA world I’ve seen is the origin of the RNA — it’s hard to make ribose prebiotically. One can do it with the Butlerov formose reaction, but that requires a big concentration of formaldehyde, and it produces sugarlike molecules with a variety of asymmetry variants. Ribose? Yes, but mixed in with a whole lot of other stuff.

    From another direction is Günter Wächterhäuser’s proposal that the reductive Krebs cycle is prebiotic. That would make the origin of life somewhat easier, since the emerging organisms could feast on Krebs byproducts and eventually run the cycle in their cells. In fact, according to some recent research, the two oldest carbon-fixation cycles are the reductive Krebs cycle and the Wood-Ljungdahl reaction, both of them likely coexisting in the same early organisms.

  65. bittys says

    (I don’t buy it; that life arose so quickly on Earth after its formation suggests that it may be relatively easy — I’d jack that up to something high)

    How do you square that with the fact that life only appears to have arisen once on Earth? Surely if it were relatively easy there would have been more than one independent occurence?

  66. Amphiox says

    The carrier waves of TV transmitters cover all of space with a complex pattern of narrow-bandwidth spikes and, as I said, are detectable by a square kilometer of collector up to ~50 lightyears away. Radar beams are transient in any one place, but the military radars cover at least the entire northern hemisphere quite often. Arecibo has covered a small fraction of the sky, but is still detectable over a huge volume – the beams are cones with narrow opening angles, but they are very very long.

    Thanks for this, michaelbusch! I had heard about these types of signals, but had always thought of them as a type of focused beam.

    But if these are not deliberately focused on a single target, but sweep the sky, how likely would an alien listener using the same protocols as we do with SETI be able to detect them? That is, if they detected the signal once, would they be able to confirm it on a second observation if we happened to be sweeping in a different direction at that particular time? Or would they end up with something like or WOW! signal but be unable to confirm?

    And if it takes a kilometer array to detect at 50 ly, at 500-1000ly (a rather optimistic estimate of the average distance between two signaling civilizations), it would take a rather colossal array to detect, wouldn’t it?

  67. Amphiox says

    The main criticism of the RNA world I’ve seen is the origin of the RNA — it’s hard to make ribose prebiotically.

    Remember, though, that the RNA World hypothesis does not require RNA to be generated prebiotically. There could have been an even older, more primitive pre-RNA world of organisms that evolved the ability to produce RNA, which then took over.

    How do you square that with the fact that life only appears to have arisen once on Earth? Surely if it were relatively easy there would have been more than one independent occurence?

    Niche exclusion. Just as with technological intelligence, but even more so. The first instance of life to get going is going competitively exclude any newer occurrences (who will start at a competitive disadvantage in not having had as much evolutionary time to optimize themselves).

    (And we don’t actually know whether or not life arose more than once on earth. We only know that only one lineage survived to be the ancestor of all extant life on earth. Before LUCA, there may well have been other lineages from independent abiogenesis events, but LUCA’s descendents outcompeted them and eliminated them.)

  68. McC2lhu saw what you did there. says

    I remember when Carl Sagan did a segment on Cosmos with the Drake Equation. I plopped in some numbers that I thought made sense (at the time) to see how many intelligent civilizations might exist in our own galaxy.

    The formula came up with an answer of .5

    At least that result is empirically verifiable. Just look at the headlines on the news from our own planet. I would think it’s being generous to say that half the world’s population are acting civilized and capable enough to communicate over distances measured in light years.

    I really hope the my own cynical numbers were wrong, though. There’s one thing that could pull our species away from its own stupidity – making contact with a distant civilization. I would hope that finally having proof of such a thing would turn the inward focus outward, and give all of humanity a shared goal of communication and creating technologies to bridge the distance to an actual meeting (assuming that the initial communications didn’t reveal the alien civilization to have some sort of sick and psychopathic overall philosophies. Then it would be back to square one, with bigger and scarier defense gadgets).

  69. puppygod says

    @28 elvenpiratefish

    @20

    It’s generally assumed that human style, tool using intelligence is a very specific niche. It’s highly unlikely that, even if two such species developed on a planet, they would not compete and one would eventually wipe out the other. Look at how the different hominids competed with each other through pre-history. For a good, though obviously not perfect example, just consider how much we compete intraspecifically, creating artificial classifications such as race to justify one groups superiority over the other.

    While I agree with you in general, problem is, we still have very limited datapoints, and there are some theoretical possibilities that simply didn’t occur on Earth, but may be true for other planets. What if the two species developed intelligence simultaneously while physically separated – for example imagine Atlantic Ocean was twice it’s size and there were some intelligent species in Americas? Or what if two intelligent species were adapted to different living conditions? Say, one living in the tropic, and one in the Arctic? Or if two intelligent species developed symbiotic survival strategy, thus eliminating competition? If dogs were intelligent, we would have two intelligent species living on Earth without wiping one another.

    @38 computerguy

    Weren’t there dinosaurs that were looking to be pretty smart before they got wiped out. Could it be the major extinction events caused it to take 4 billion years for technological life to develop.

    There are pretty smart dinosaurs living today – for example Grey Parrots. But with all their high intelligence they are still not on the level of making woven fabric clothes or using fire, not to mention building radiotelescopes.

    It seems, that for human-like intelligence to develop there is a need for several high-gain high-cost adaptations to occur at the same time. Intelligence needs social structure, ability to communicate, ability to pass culture (that includes taking care of their young), ability to make and use tools etc.

    @73 bittys

    How do you square that with the fact that life only appears to have arisen once on Earth? Surely if it were relatively easy there would have been more than one independent occurrence?

    That’s very valid point, and the answer is – we don’t know. We know very little about the early life (even if there was some tracks in the rocks thanks to the continental drift all the rocks from the times of early life are re-melted now). It is entirely possible, that there was more than one instance of abiogenesis – most common hypothesis being that most adapted variant of early life outcompeted and basically eat all other lifes (lives? We don’t even have proper plural). And then habitat-changer ability of life kicked in and there were no more conditions for abiogenesis present.

  70. says

    Drake himself said that the idea of the equation (which as jasonnishiyama pointed out at comment #64, was prior to the 1961 SETI conference) was to act as a means of “organising our ignorance”, to see if there was even any point in attempting to search for extra-terrestrial transmissions by radio telescope.

    Fifty years later, we are slightly less ignorant, as lpetrich points out in comment #72 above: where people like Drake or Sagan had to guess at the fraction of stars with planets and the average numbers of planets in those star systems from no data whatsoever, since 1989 we’ve discovered over eight hundred exoplanets, which must allow us to have a very slight amount of increased confidence in assigning a somewhat meaningful number to both those variables.

    Yes, of course the BBC applet is a ouija board, as we are completely ignorant of some of the remaining variables and likely to be ignorant for centuries to come – so one thing I’d love to see implemented on it are being able to define separate confidence margins (or ranges) for each of the variables, so that it can be shown how widely our ignorance on each of the variables effects the final result.

    Since I seem to recall you’ve had a go at mocking the Drake equation, PZ, are you saying that thought experiments aren’t useful, ever? Or that the various attempted answers to the Fermi paradox aren’t interesting to consider?

  71. birgerjohansson says

    Corvids and parrots have powerful brains for their size, but since flight is so important for them they suffer from a weight limit.
    Also, the forelimbs are specialised for flying, leaving the beaks and hindlimbs for gripping.

    Great apes and our own ancestors are privileged by comparison.

    All land-living vertebrates have myelin sheeting around the neurons, cephalopods must cope by having very thick neurons instead. So vertebrates are privileged.

  72. lpetrich says

    Going from fl to fi in the Drake equation, one can identify several steps along the way.

    Autotrophic energy metabolism – no more dependence on the primordial soup/pizza/sandwich. The oldest form of this is likely chemoautrophy — electron-transfer metabolism using the respiratory chain, though with oxidizers like nitrogen oxides. It’s coupled to cell membranes, where it extracts energy using the chemiosmotic mechanism. Pumping hydrogen ions out of the cell, and allowing them back in to assemble ATP.

    Photosynthesis – emerged twice. In Archaea, it uses bacteriorhodopsin, and plugs into the chemiosmotic mechanism. In Eubacteria, it uses chlorophyll, and plugs into the respiratory chain. The latter also does biosynthesis, and the most common version of it uses water as an electron source. Difficult but very common, allowing spread into a variety of new habitats. Oxygen could fuel a lot of complexity in eaters of these organisms.

    Multicellularity – emerged numerous times; I’ve seen an estimate of at least 25 times. But most times have been plantlike or funguslike, with only one animallike case, the animal kingdom itself, though choanoflagellates could also be counted with it.

    So is animallike multicellularity difficult to evolve?

    An assist to becoming large is having an internal skeleton. Only vertebrates have skeletons well inside the body, as opposed to its surface or just below the skin. So is that also difficult to evolve?

    Living on Land – Necessary for building radiotelescopes and the infrastructure necessary to build and support them. Animals went on the land several times, though vertebrates did it only once (insects, spiders, myriapods, isopods, land crabs, earthworms, leeches, land snails/slugs). Plantlike organisms did so only once, while funguslike ones did so more than once (true fungi, oomycetes).

    Multigenerational societies – Necessary for transmitting learned information down the generations, like how to build a radiotelescope. It has evolved several times.

    Language – Human-scale language is necessary for describing how to build a radiotelescope. We are the only present-day species that has it, with the possible exception of some cetacean species. Our great-ape relatives are far behind.

    This can make shoddy reasoning very annoying, because it’s always stated with language that’s far beyond the capabilities of most species.

  73. lpetrich says

    Amphiox is correct about the possibility of a pre-RNA world. I’ve seen speculations about peptides (protein fragments) and polycyclic aromatic hydrocarbons as ribose predecessors.

    As to grasping organs, they evolved several times. Jaws and manipulative limbs have evolved more than once. Pincers, tentacles, fingers, …

    It’s necessary to have them to build radiotelescopes, so birds have painted themselves into an evolutionary corner with their front limbs being specialized as wings. Some non-flight-adapted fellow theropods back in the Mesozoic could have had a better chance, however.

    Dolphins have it even worse, living in the water and lacking manipulative limbs.

  74. KG says

    The only data we have about how difficult various developments from abiogenesis to capability for interstellar communication are, comes from how long they took to occur, and whether as a result of a single, apparently fortuitous occurrence, repeated independent occurrences, or gradual change. Abiogenesis seems to have occurred quickly; so when conditions allow, as PZ says, we can guess that it is highly probable (but we don’t know how specific the preconditions are). Complex cells, however, seem to have developed only once (eukaryotes), through endosymbiosis, and only after getting on for 2 billion years; so that looks like a narrow bottleneck: while bacteria have evolved some kinds of quasi-multicellularity, none of these show the kinds of hierarchical complexity found in multicellular eukaryotes. Eukaryotic multicellularity has evolved a number of times, and intermediate stages are known (e.g. choanoflagellates); but only one of these has led to intelligence – so the “right kind” of multicellularity may be rare. Once central nervous system evolved in one line of Metazoa (the Bilateria), my impression is that maximal CNS complexity increased almost monotonically over time, so I disagree with PZ that intelligence looks like a “weird and unlikely adaptation”, once something with a CNS has evolved. The increase in technological capability also looks near-monotonic from a couple of million years ago to the present. The last bottleneck may well be that technological civilizations usually (or always) undermine the environmental conditions of their own existence, and so do not last long.

  75. scottde says

    Note that the percentage is the chance that intelligence will evolve at some point during the time the planet is habitable. So based on the Earth the odds are 100%. All you need for a planet to count is for intelligence to evolve once during the 6-8 billion years the planet is habitable. Intelligence doesn’t have to evolve particularly quickly for the percentage to be high.

  76. michaelpowers says

    While life out there may be plentiful, intelligent life faces additional challenges. I suspect that once a species gains the ability to imagine it’s own mortality, it invents something akin to religion, and in doing so, seals it’s fate.

    Here on Earth, I often wonder whether sentience itself is an evolutionary dead-end.

  77. Amphiox says

    Well, if anyone observes a crow or parrot for a while and sees what they can do with their hind claws and beak, the lack of manipulating forelimbs doesn’t seem such a big hindrance. The size constraint from flight is probably bigger, but then many bird families have evolved flightlessness and gotten bigger.

    An aquatic intelligence might (though we can’t say for sure) be disadvantaged in discovering things like fire and metallurgy, but even assuming such things are actually impossible in an aquatic environment, if they develop technological capability even of a low degree, there’s nothing that actually stops them from colonizing/exploring land, or building floating constructs to access resources (ie gases for fire) in the atmosphere. Fire for them might be a late discovery, after their agricultural/domestication revolution, instead of before.

  78. gussnarp says

    Sorry if I missed this and someone already said it, I missed this item while it was hot off the press, but it seems to me that the minimum allowable figures for some entries are simply much too high. Chance that a civilization can communicate across space has a minimum of 1%. Why should that be the minimum? If by “communicate across space” we mean send a signal that reaches earth and is still intelligible (and remember, this equation is supposed to be about us making contact, right?) then I’m going to have to say, based on available evidence, that this probability should be much lower than one percent. Same with intelligence capable of radio (or similar) communication arising. We got one species in 4 billion years, as you said. So the problem is not with a preset, it’s with the minimum available. The probability of life evolving, judging from our admittedly small sample size, is much lower than 1%. The best we can say is that it’s probably at least one in a billion. Maybe quite a bit better, but it’s tough to say.

    I think their preset for habitable planets in a solar system is awfully high too. It’s more than one. So far we’ve got one habitable planet in all solar systems. No one has yet shown that the conditions for life exist on any other planet we’ve found, anywhere. So I put that one at 0.1. Also, a possibly too high minimum setting.

    I also think the problem with the Drake equation is the units you end up with: number of civilizations. The question isn’t how many intelligent civilizations are out there, it is the probability that even one of them ever makes contact with Earth in any way. That there are likely to be a large number in our enormous universe is meaningless given that almost all of them are completely prohibited from ever having contact with Earth based on our current understanding of physics. Even if one of them actually arose in our galaxy and had a chance of getting a signal here, which would be interesting, there’s virtually no chance of a meaningful two way communication. Whoever sent the signal would have been dead for centuries before we received it, and we would be dead for centuries before they received our response. Who knows if anyone would even remember that they sent the signal, or if anyone of the same species, let alone civilization, would be left.

  79. elvenpiratefish says

    I will point out that I had stated many times earlier I agree that we don’t have enough of a data set to make any real conclusions on the likelihood of intelligence. I’m merely taking the skeptical approach in this debate and saying that the one example we do have would indicate that advanced intelligence is rare and has specific requirements. My own understanding of biology (which I will admit is a few years out of date as I received my bachelors eight years ago and haven’t been working in the discipline since) would lead me to conclude that some of these requirements can be logically derived from Homo Sapien Sapien.

    The one’s I feel are pretty much a must for any species to develop advanced intelligence are (with explanations included):

    Terestrial: Aquatic environments do not lend themselves to advanced tool use, the buoyancy of the environment makes construction of most structures superfluous and materials hard to come by. Even the most resource rich aquatic environments will tend to be low on materials due to there being no need to deal with gravity. This is why you don’t see woody plants evolving in aquatic environments

    Omnivorous: Advanced intelligence requires large amounts of energy to maintain and function, which tends to mean that you need high calorie density in your food to support it. However, while predation is better for this in the early stages, once a species develops plant domestication that quickly outstrips what you can achieve from hunting or even animal husbandry.

    Endothermic: This one is mainly because endotherms have an inate advantage in terms of biological functioning by maintaining their bodies at the ideal temperature for biochemical reactions (in theory) as well as giving them a much wider range of temperatures and climates they can live in. This could be countered of course by living in an extremely stable temperature environment, but that would add other constraints to species expansion which would not be condusive to advanced technology.

    Now, those traits then need a propper environment to favor intelligence. The latest science I’ve heard on this indicates that what is needed is very high environemental instability. The idea being that such conditions would tend to favor species that have an adaptation which gives flexibility. The idea being that when the environement is so unstable, an adaptation that only helps in one set of conditions is useless, and intelligence’s big advantage is the flexibility it gives us. If the climate gets overly dry for a few years we can use abstract thinking to find alternate sources of water.

    Are there other factors? Definitely, but I feel fairly confident that these things are at least some of the prerequisites for advanced intelligence to evolve. The question then becomes how hard it is to get the right set of conditions for those things to align correctly, which will only be answered when we have more then one planet to go off of.

  80. dysomniak, darwinian socialist says

    @elvenpiratefish The problem with all of your assumptions (and of course any variables conjured up for the equation) is that you are basing them on life on earth. There is no empirical reason to believe that life on earth is in any way representative of what is typical on other worlds, and all your rationalizations are merely that. Like an evo-psycher you’ve come up with a very compelling ‘just so’ story that explains, post hoc, why the only technological species on earth has the traits it has.

    Advanced intelligence requires large amounts of energy to maintain and function, which tends to mean that you need high calorie density in your food to support it.

    Don’t be so sure.
    http://www.nature.com/nature/journal/v480/n7375/full/nature10629.html
    http://paleovegan.blogspot.com/2011/11/its-curtains-for-expensive-tissue.html

  81. KG says

    My own understanding of biology (which I will admit is a few years out of date as I received my bachelors eight years ago and haven’t been working in the discipline since) would lead me to conclude that some of these requirements can be logically derived from Homo Sapien Sapien. – elvenpiratefish

    *sigh*
    If you’re going to use a technical term in order to sound sciency, it helps to get it right. The scientific name for our subspecies is Homo sapiens sapiens. The italics are required, the species and subspecies designation are all lower-case, and it’s sapiens not sapien.
    p.s. I ceased my formal education in biology at age 16.

  82. KG says

    That there are likely to be a large number in our enormous universe is meaningless given that almost all of them are completely prohibited from ever having contact with Earth based on our current understanding of physics. Even if one of them actually arose in our galaxy and had a chance of getting a signal here, which would be interesting, there’s virtually no chance of a meaningful two way communication. Whoever sent the signal would have been dead for centuries before we received it, and we would be dead for centuries before they received our response. – gussnarp

    This assumes that lifetimes will remain limited to the scant century or so we currently live, however technically advanced the civilization; and ignores the possibility of technologically advanced civilizations sending out artificially intelligent >von Neumann probes. I see no grounds whatever for doing either.

  83. lpetrich says

    Going from fi to fc, we have only our species to work from, and we find some interesting difficulties.

    Whare are our big brains specialized for? I’ve seen the “social brain” hypothesis, of being specialized for social interactions. In fact, the mazimum size of a social group where everybody knows everybody else scales with brain size, and it is about 150 for our species: Dunbar’s number.

    This would mean that we are specialized for being social yakety-yaks. That might offer a motive to build radiotelescopes, but not any expertise in doing so.

    Cognitive specialization? I’ve seen speculation about schizophrenia and shamanism, and something similar could be behind autism and Asperger’s syndrome. In effect, that some of us are mentally specialized for getting expertise that the rest of us find difficult to acquire and use. This seems like a kludgy adaptation, but I’ve seen clinical depression explained as a way of unlearning troublesome behavior patterns: Is Depression An Adaptation?, making it another kludgy adaptation.

    Agriculture – One needs groups of more than 150 sentients to work out how radiotelescopes are worth building and to design and make radiotelescopes, and among us, that was made possible by agriculture: domesticating plants and animals that are good for food, raw materials, and labor. It was invented several times after the end of the last Ice Age, though for some reason, not during it or not during the previous big interglacial about 100 thousand years ago. The timing of its invention continues to be a mystery.

    Writing – This was invented a small number of times, but it spread by borrowing existing writing systems and by stimulus diffusion: the hint that writing was feasible and worth doing. Writing increased the amount of information that could be passed down the generations, but it likely provoked opposition from memorizers of large amounts of information, its predecessor. We don’t have much on that, possibly because of societal natural selection: the people who write a lot are people who think that writing is a Good Thing. But about 2400 years ago, Plato imagined in Phaedrus someone objecting to writing that it would make our memories atrophy and allow us to have a fake sort of understanding. His society had become literate for the second time only a few centuries earlier, borrowing it from the Phoenicians.

    Science – as an explicit method, that’s been hard to develop. The Greco-Roman world came close, but Richard Carrier has proposed that it was cut short by the strife of the Roman Empire’s Crisis of the Third Century. Only over a millennium later did science get restarted. So it seems to me that there were some odd turns of events involved along the way.

  84. David Marjanović says

    The Rare Earth equation: contains a bunch of terms that are missing from the Drake equation by oversight.

    Worldwide, there is no shortage of food, there is also no technical problem with transporting food from areas of surplus to areas of deficit.

    Those 30,000 deaths are a political problem, not a scientific one.

    Cannot be said often enough!

    You mention only one intelligent form of life evolving on Earth, but I was curious, did Neanderthals evolve intelligence separately from Homo Sapiens or was it already developed (or developing) prior to speciation? Were we even entirely separate species by they time Neanderthals disappeared or is that still a topic being debated?

    1) Homo sapiens. No capital letter in the middle, and italics.
    2) Define “intelligence”. I’m sorry to sound snarky, but I really can’t answer your question without understanding it in much more detail. Chimpanzees sometimes hunt with spears…
    3) Define “species”. If you mean “able to have fertile offspring”, then no: all humans alive today who don’t have recent African ancestry carry up to 4 % of Neandertal DNA in their genome.
    4) If you assume separate evolution, you assume two events. If you don’t, you only assume one event. The latter is more parsimonious.

    Yeah, like this useless poindexter dude. Norman Borlaug

    Made possible the lives of two billion people.

    Then maybe intelligence was not an adaptation but a random event or series in the human lineage. Isn’t that the null hypothesis anyway?

    Sexual selection does seem to be involved.

    “…and our kind of intelligence popped up once in 4 billion years.”
    We actually don’t know how many time “our” kind of intelligence has “popped” up. We don’t know what type of intelligence the Neanderthals had, for example. We just know that we’re only one with our kind of intelligence that has managed to survive.

    Pft. 40,000 years are much less than the error bar on the 4 billion!

    Also, we can be quite sure that no civilization at all like ours has been present on Earth before.

    I once read about (!) a scifi story that featured such a previous civilization on Earth. It had to be put in the Precambrian and had to be given a cultural obsession with really-long-term recycling or something so it would only build on subduction zones…

    Sapien

    There is no such word.

    There actually HAS been a rough trend over the course of multicellular animal life on earth for the species with the greatest intelligence to get progressively smarter.

    No. The span from smallest to largest brains, the diversity, has been increasing. And I’d like some citation for the difference between the Carboniferous and the Triassic.

    The same, in fact, is roughly true for cephalopods, too (ancient ammonites and nautiloids were dumb compared to modern cephalopods), though our fossil record of their brains much more patchy.

    That’s an incredibly optimistic way to put it!!!

    I once had the thought: What if there were no birds? What might humans have missed? We take them so much for granted, but perhaps one passing overhead caused someone to look up and really notice the sky or clouds or stars.

    Bats. Perhaps pterosaurs.

    The main criticism of the RNA world I’ve seen is the origin of the RNA — it’s hard to make ribose prebiotically.

    Then start with threose or even glyceraldehyde.

    It seems, that for human-like intelligence to develop there is a need for several high-gain high-cost adaptations to occur at the same time. Intelligence needs social structure, ability to communicate, ability to pass culture (that includes taking care of their young), ability to make and use tools etc.

    Gray parrots have all that. What they don’t have is any need to do more with their abilities than they do today. There’s no selection pressure in such a direction.

    Since I seem to recall you’ve had a go at mocking the Drake equation, PZ, are you saying that thought experiments aren’t useful, ever?

    Whut? Where are you getting that from?

    Or that the various attempted answers to the Fermi paradox aren’t interesting to consider?

    Whether the Fermi paradox exists depends on the solution of the Drake equation – or rather the Rare Earth equation.

    As to grasping organs, they evolved several times. Jaws and manipulative limbs have evolved more than once. Pincers, tentacles, fingers, …

    It’s necessary to have them to build radiotelescopes, so birds have painted themselves into an evolutionary corner with their front limbs being specialized as wings. Some non-flight-adapted fellow theropods back in the Mesozoic could have had a better chance, however.

    Parrots can do a lot with beak and toes. Don’t underestimate them.

  85. elvenpiratefish says

    @kg

    Sorry that I didn’t italicize, as html tags are not my strong suit and I tend to not use them.

    @dysomniak

    The points I used were all made based on observed physics and chemisty. Aquatic environments are highly stable, and unless the chemistry of water is vastly different on other planets it’s safe to assume it has the same traits everywhere.

    The point towards omnivory, I will grant, I had not seen the paper refuting the ETH, though brains still are very expensive and on a pure chemistry point of view, energy density vs time is important in the development of advanced intelligence and civilization. Human civilization only advanced once we could reliably improve how much food we were getting vs time put into getting it. Omnivory, I believe, would still be favored because it gives a species more options in any given situation to pick the food source with the best energy density vs time.

    Endothermy, again is about chemistry and flexibility. How a species attains endothermy could be vastly different from us, I fully allow, but the phenomena itself is what’s important. Logically, a species on any planet would have to thermoregulate, either ectothermically or endothermically; there really aren’t that many basic options in this category.

  86. KG says

    I suspect that once a species gains the ability to imagine it’s own mortality, it invents something akin to religion, and in doing so, seals it’s fate. – michaelpowers

    I think it’s more likely capitalism than religion that does this: so far, all experience indicates that it will use ever-increasing raw materials, and produce ever-increasing pollution; and it has shown its power to incorporate even social systems set up explicitly to supercede it.

  87. KG says

    @elvenpiratefish,

    That’s one of the three errors you made. No html tag is necessary to produce “sapiens” in place of “Sapien”.

  88. elvenpiratefish says

    I see, so the fact that I had a mispelled a word and missed decapitalizing something some how refutes my other statements? If I was writing a formal paper, which I haven’t had to do in eight years, I would have sent it through multiple error checks before submitting it; I didn’t realise that a comment thread required such vigorous editing. I will make sure to submit my future posts through the appropriate peer review prior to submitting them so that you do not need to deal with a simple typographical error while perusing the internet.

  89. Amphiox says

    I think it’s more likely capitalism than religion that does this: so far, all experience indicates that it will use ever-increasing raw materials, and produce ever-increasing pollution; and it has shown its power to incorporate even social systems set up explicitly to supercede it.

    While this process is certainly likely to bring about the downfall of civilizations, it isn’t at all clear that it is guaranteed to produce the extinction of the species, and in the absence of that there remains the possibility of recovery. We should not assume that detectability time is therefore a one-shot deal.

    We may instead see a repeated on/off pattern as a technological civilization achieves broadcast ability, broadcasts for a while, collapses and loses the capability, recovers and regains that ability, and on and on.

    And we shouldn’t rule out the possibility that new intelligences may evolve after the first intelligence goes extinct.

    In fact I would hypothesize that the artifacts left behind by the first intelligence may help potentiate the development of later intelligences, making the evolution of a second or third intelligent species easier than the evolution of the first. (Even ignoring the possibility of the first species deliberately uplifting a second).

  90. Amphiox says

    Aquatic environments are highly stable

    This one I would dispute. Some aquatic environments are stable. Not all. (And some terrestrial ones as well).

  91. Amphiox says

    Gray parrots have all that. What they don’t have is any need to do more with their abilities than they do today. There’s no selection pressure in such a direction.

    There may well be selection currently against going in such a direction. Any lineage that evolves in a direction more likely to put it in direct competition with humans is going to find itself in trouble.

    But if we were removed from the picture, all bets are off….

  92. Amphiox says

    No. The span from smallest to largest brains, the diversity, has been increasing.

    Does it not amount to the same thing? Since there is a limit on how small the smallest brain can be, before it ceases to be able to function as a brain, and the earliest brains were already at that limit, the net result of this increase in diversity is that the biggest brains at any given time has, roughly on average, been increasing over time.

    (Until such time that the brains hit a physiologic upper limit to size. Which possibility might be around now, with human brains, though of course we don’t know that for certain)

    And I’d like some citation for the difference between the Carboniferous and the Triassic.

    I was hoping someone like you would chime in with the reference, actually. :-) Was it not common knowledge that the earliest triassic dinosaurs and mammals/late protomammals had slightly larger brains than the Carboniferous amphibians and early reptiles?

  93. Amphiox says

    The Rare Earth equation: contains a bunch of terms that are missing from the Drake equation by oversight.

    The Rare Earth equation is kind of tainted, I think, since it was developed with significant input from then-closet-creationist astronomer G. Gonzales, and many of the terms are really questionable to me as ad hoc attempts to make earth unique.

    Some form of a rare earth equation, though, is probably closer to the truth (ie something with more variables added to it than just the Drake Equation).

  94. elvenpiratefish says

    @Amphiox

    Yes and no; for example temperature wise the ocean is very very stable. Typically the difference in temperature from one part of the ocean to another is less then a degree. This is because of water’s high specific heat, so generally climate change has a reduced effect. Marine environments are also buffered from astronomical events such as asteroid strikes. These are just a couple of the reason that the average “life span” of a marine species is about 5 times as long as that of a terrestrial species. This isn’t to say that mass extinctions don’t hit oceans, they obviously do, but usually the die off is far lower in the ocean then on land and, as is often the case, it’s the large animals that are most affected.

  95. David Marjanović says

    It was invented several times after the end of the last Ice Age, though for some reason, not during it

    Ice ages have very unstable climates, not predictable enough for agriculture.

    That’s also why agriculture hasn’t been invented in Australia: rain is too random there.

  96. David Marjanović says

    I see, so the fact that I had a mispelled a word and missed decapitalizing something some how refutes my other statements?

    What? It has no bearing on anything else you’ve said.

    …except that it leaves a bad impression of your general knowledge of biology.

    No. The span from smallest to largest brains, the diversity, has been increasing.

    Does it not amount to the same thing?

    No – it doesn’t (necessarily) amount to a steady increase in the ancestral lineage of any extant bloat-brains. It doesn’t (necessarily) amount to any driven trend at all, just a branching random walk.

    Was it not common knowledge that the earliest triassic dinosaurs and mammals/late protomammals had slightly larger brains than the Carboniferous amphibians and early reptiles?

    Not as far as I know.

    The Rare Earth equation is kind of tainted, I think, since it was developed with significant input from then-closet-creationist astronomer G. Gonzales, and many of the terms are really questionable to me as ad hoc attempts to make earth unique.

    Interesting; but I can’t find any factors that seem irrelevant.

    Marine environments are also buffered from astronomical events such as asteroid strikes.

    Except the biggest ones that drench the top layers in acid.

    “life span” of a [...] species

    BZZZT! Wrong.

    For that to be a remotely measurable quantity, you’d have to use the same species concept for everything. Good luck. Depending on the species concept there are from 101 to 249 endemic bird species in Mexico.

  97. Amphiox says

    This isn’t to say that mass extinctions don’t hit oceans, they obviously do, but usually the die off is far lower in the ocean then on land and, as is often the case, it’s the large animals that are most affected.

    This, to my knowledge, is not true. In both the PT and KT mass extinctions (the two biggest in history), the die off was substantially worse in the ocean. In the PT, the die off in the ocean was >95%, on land “only” 90%. In the KT, the die-off in the ocean was close to 90%, on land around 70%.

  98. Amphiox says

    No – it doesn’t (necessarily) amount to a steady increase in the ancestral lineage of any extant bloat-brains. It doesn’t (necessarily) amount to any driven trend at all, just a branching random walk.

    But I wasn’t referring to any specific one lineage. I was talking about the small group of species with the biggest brains in the biosphere, whatever they are, and whatever their ancestral lineages are, at any given time.

    ie, take the entire biosphere as a whole, find the biggest brains, irrespective of lineage, and plot their size (actually EQ) against time. You get a scatter plot with a trendline going up.

    Because from the perspective of finding intelligence on another world, it doesn’t matter which species are the intelligent ones or what lineage they arose from, only whether or not they are there.

    A branching random walk where there is a boundary condition at the low end, and which starts near the low end, has to, by statistical law, produce a trend of gradual increase until it reaches a boundary condition on the high end.

    If you take a population of numbers, with the stipulation that they must be greater than zero and less than one thousand, and then randomly generate descendent numbers that are either +1 or -1 the ancestor, randomly, if you start with a population of 1’s and 2’s, your completely random scenario WILL result in the biggest number in the population getting steadily bigger with time, until you hit 1000.

  99. KG says

    I see, so the fact that I had a mispelled a word and missed decapitalizing something some how refutes my other statements? – elvenpiratefish

    I didn’t say it did. I said:

    If you’re going to use a technical term in order to sound sciency, it helps to get it right.

    If you can’t be bothered to get technical terms right, don’t use them; there was no need to use a technical term where you did.

  100. Amphiox says

    Interesting; but I can’t find any factors that seem irrelevant.

    It’s just my opinion, but I think the reasoning behind fm(large moon), fj(jovian), fme(mass extinctions) are completely “just-so story” type reasoning, and with our current state of knowledge, the declared directional effect given to these factors (that their absence reduces the likelihood of complex life, or that earth’s special configuration of these factors is the only one that can produce complex life) is the result of wishful thinking on Gonzales’ part because he wants for religious reasons the earth to be unique.

  101. duckdunn says

    PZ wrote:

    Apparently, the % chance a habitable planet develops life is guessed at 13% (I don’t buy it; that life arose so quickly on Earth after its formation suggests that it may be relatively easy — I’d jack that up to something high),

    It’s certainly tempting & intuitive to make that argument. However, this recently published paper claims that given life arose so early in Earth’s history doesn’t necessarily imply anything about the frequency of life arising on other habitable planets. If we even acquire one more data point though, it will make a big difference. (I’m not qualified to have an opinion on this paper; I’m just reporting it.)

    Bayesian analysis of the astrobiological implications of life’s early emergence on Earth

  102. Amphiox says

    Apparently, the % chance a habitable planet develops life is guessed at 13% (I don’t buy it; that life arose so quickly on Earth after its formation suggests that it may be relatively easy — I’d jack that up to something high)

    It may be that those deriving this percentage are using the current astronomical definition of a potentially habitable planet, which is rather limited (basically just with a stellar influx that could put the potential surface temperature within the range that allows for liquid water dependent on the composition of an unknown atmosphere, and a size/mass between Mars and 5-10X Earth). By this definition, in our own solar system, all three of Venus, Earth, and Mars qualify (which puts the % down to 33% right there) by this definition.

    So basically they’ve lowered this term to compensate for overestimating the prior term. If you restrict your planets to more “earth-like” ones, you’ll increase this term, but you’ll lower the previous term.

  103. Amphiox says

    However, this recently published paper claims that given life arose so early in Earth’s history doesn’t necessarily imply anything about the frequency of life arising on other habitable planets.

    This is basically the argument I’ve made about a whole lot of other earth-based observations and their extrapolations.

    NOTHING observed about earth necessarily implies anything about the frequency of life arising on other habitable planets.

    We REALLY need that second data point.

  104. puppygod says

    By this definition, in our own solar system, all three of Venus, Earth, and Mars qualify (which puts the % down to 33% right there) by this definition.

    It might be 66%. While Venus is out of the picture, it is still to early to conclude that there was no life on Mars in the past. Which raises another interesting point – while Earth-like planets within Goldilocks zone might be common, we don’t have a clue about timescales on which they remain habitable. Your planet loosing atmosphere, changing orbit or crashing into other planet, or your star frying all life with gamma-burst is a show-stopper no matter how far you evolved from primordial soup. Unless you have inter-stellar travel capability before that happens.

  105. says

    @Amphiox @74:

    You can detect weak omnidirectional signals to much larger distances than the nominal limit if you integrate in time. That means you can’t decide what the aliens were saying, but you know that they were there.

    The limits I gave were worked out for a signal giving a hypothetical ET SKA 10 photons per bit of information on a 0.1 Hz signal. If you integrate for a hundred thousand seconds rather than 10, the limiting distance goes up by a factor between 10 and 100.

  106. lpetrich says

    The final parameter is L, the lifetime. To make L large requires tapping some source of industrial-grade energy that can last a LOT longer than fossil fuels. There do exist some, like wind and solar, and and we are getting good enough with them to make them compete with fossil fuels. However, that might not be good enough to get us out of the fossil-fuel trap that we are now in.

    If one has enough energy, one can do more-or-less anything, including extracting rare chemical elements or making them with nuclear reactions. So that many not be much of a problem — only dependence on easy-to-exploit ore bodies that may run out relatively quickly.

  107. Amphiox says

    It might be 66%. While Venus is out of the picture, it is still to early to conclude that there was no life on Mars in the past. Which raises another interesting point – while Earth-like planets within Goldilocks zone might be common, we don’t have a clue about timescales on which they remain habitable.

    One has to factor in the fecundity of a habitable planet as well. Mars, even if habitable (and Europa and Enceledas too), will certainly be much less fecund than earth.

    Earth is absolutely covered with life. You could literally drop a probe randomly, anywhere on earth and randomly scoop a sample, and if you know what to look for, you’ll almost certainly find life. But a planet like Mars not so much. There could be habitable planets on the borderline of habitability that are not covered in life, but only support life in specific locations/habitats.

    An intelligent technological species probably needs a relatively fecund biosphere.*

    So the likelihood of an intelligent civilization arising on a planet like Mars may be much lower than for a planet like Earth*. Maybe it is even zero for a planet like Mars.

    *Of course, here I am doing the same extrapolating from a sample set of one** that I’ve criticized.

    **But if we didn’t do it, we’d have nothing to talk about at all. It’s just something to remember when considering the level of certainty of our various deliberations.

  108. Amphiox says

    Your planet loosing atmosphere, changing orbit or crashing into other planet, or your star frying all life with gamma-burst is a show-stopper no matter how far you evolved from primordial soup. Unless you have inter-stellar travel capability before that happens.

    Well, advanced terraforming capacity, if not starflight, for some of these.

    A gradual loss of atmosphere over several millions or ever just tens of thousands of years could theoretically be countered.

    A gamma-ray burst could potentially be shielded against using subterranean shelters. Of course the civ would have to have the foresight of being able to assess the risk of be bursted in their neighborhood and prepare contingencies, since you can’t have any warning of a gamma ray burst after the fact, since it travels at the speed of light.

    Orbital change may be compensated for by terraforming your atmospheric greenhouse efficiency. And if you were REALLY capable, you might be able to change the orbit back.

    Crashing into another planet probably does require starflight capability to survive.

    Suppose for example if the process that rendered Mars inhabitable through atmosphere and water loss started to happen on earth right now, and we found out about it. It takes several million years to occur. Could we survive it, starting with just present day technology? I actually think we could.

    (Assuming we don’t just deny it’s happening, or decide that going extinct in 10 million years isn’t a problem worth dealing with…..)

  109. Amphiox says

    While Venus is out of the picture, it is still to early to conclude that there was no life on Mars in the past.

    We can’t actually conclude that Venus too didn’t have life in the distant past. It’s just that, since Venus experienced a crustal turnover event where its entire crust melted and re-solidified about half a million years ago, and any life that might have existed on Venus* is thought have been there billions of years ago, finding any trace of it now is basically impossible.

    *though the hypothesis has been batted around that there might be a layer high in the Venusian atmosphere where the pressures and temperatures are within the range where droplets of water could exist and where earth-type prokaryotes could, possibly, survive, so even Venus isn’t completely ruled out for habitability.

  110. David Marjanović says

    No – it doesn’t (necessarily) amount to a steady increase in the ancestral lineage of any extant bloat-brains. It doesn’t (necessarily) amount to any driven trend at all, just a branching random walk.

    But I wasn’t referring to any specific one lineage. I was talking about the small group of species with the biggest brains in the biosphere, whatever they are, and whatever their ancestral lineages are, at any given time.

    I’m saying none of those lineages necessarily either keeps growing bigger brains or dies out. It may stagnate – whale brains don’t seem to have grown in tens of millions of years, or elephant brains for not quite as long – or presumably reverse the trend; some other lineage will, by sheer chance, take its place. Or not.

    ie, take the entire biosphere as a whole, find the biggest brains, irrespective of lineage, and plot their size (actually EQ) against time. You get a scatter plot with a trendline going up.

    But you can’t use scatter plots in biology. You have to take the tree into account always, at all times, because the data points are not independent. Nothing in biology makes sense except in the light of evolution; nothing in evolution makes sense without a phylogeny.

    The latest word on the subject: http://sysbio.oxfordjournals.org/content/59/6/689.abstract

    I think the reasoning behind fm(large moon), fj(jovian), fme(mass extinctions) are completely “just-so story” type reasoning

    They make a lot of sense to me.

    Venus experienced a crustal turnover event where its entire crust melted and re-solidified about half a million years ago

    Half a billion. :-)

    Venusian

    (That should actually be veneric… or venereal.)

  111. says

    “Venerian” or “Venerean” are also acceptable adjectival forms of Venus.

    Also, (pedantry alert!), there is no “PT” extinction. Although even journal editors miss this, there are formal abbreviations for the Periods of the Phanerozoic. The “T” goes with the (no longer formal) “Tertiary Period”. The formal symbol for the Triassic is a capital T with a small capital R attached to the stem: as this is not a standard ASCII symbol, an acceptable version of it is “Tr”. So it is the PTr (or P/Tr) extinction. A “PT extinction” implies a Permian-Tertiary boundary, which is better known as the entire Mesozoic Era!

    Similarly, the one at the end of the Cretaceous is the KPg (since the Tertiary is no longer a valid system/period, and has been replaced with the Paleogene and Neogene).

  112. ChasCPeterson says

    But you can’t use scatter plots in biology.

    Sure you can.
    You mean (I guess) you can’t analyze comparative data as if they were independent. The article you linked advocates independent contrasts plotted against estimated node ages (I think). So you calculate your independent contrasts and make a scater plot whith them.

  113. ChasCPeterson says

    first sentence blockquote
    I’m not actually arguing with myself.
    Yes I am.
    No I’m not.

  114. Amphiox says

    I think the reasoning behind fm(large moon), fj(jovian), fme(mass extinctions) are completely “just-so story” type reasoning

    They make a lot of sense to me.

    Well let’s consider them: (anyone with more astronomy expertise please feel free to chime in)

    1. Large moon, with rationale being a) stabilization of orbital tilt and stabilization of climate and b) the impact was necessary to kickstart plate tectonics on earth

    a) i) While it’s reasonable that stabilization of climate can promote the evolution of complex life, that by no means suggests that earth’s configuration is the ideal one. The optimal degree of climate stability could be either less than or greater than earth’s. A higher degree of climate instability will generate more varied conditions that cycle more rapidly, increasing selection pressure, and below a certain limit, would be expected to promote the evolution of complex life. While a completely stable climate might not promote much evolution at all. So how big a “big” moon do you really need, and does a “big” moon have to come from impact? Could you get from capture of another planetisimal? Suppose Earth didn’t collide with Theia to produce to moon, but captured Theia into a double-planet style system instead?

    ii) The instability of orbital tilt on a terrestrial planet is the result of gravitational interactions with other planets. The tilts of earth and mars change because of interactions with each other and Venus. What if there aren’t any other planets? What if the system had a Jupiter analog, an earth analog, and nothing else in the inner system? What would perturb the tilt of the earth-analog then?

    b) i) Simulations of super-earths suggest that plate tectonics will more easily get started on these planets due to their greater mass and retention of heat. Earth may actually be a borderline case on the small end that was helped by the additional heat of a big impact. Furthermore, there are a wide variety of impact configurations that are sufficient for producing plate tectonics – it isn’t restricted to just the rare angles that produce a big moon. And all earth-like planets will experience many large impacts during their formation.

    2) Jupiter. The reasoning being that a Jupiter mass planet reduces the number of impacts, but it is actually unclear if Jupiter’s net effect in our solar system is to reduce or increase the number of impacts. IIRC, the KPg impactor is thought to be from the Baptistina family, and was kicked into an earth-crossing orbit by Jupiter. Also the constrainsts on where a Jupiter sized planet needs to be to be effective at deflecting asteroids are pretty wide. (And then there is the issue of just how often a large impact actually produces a mass extinction. Only one of earth’s 5 big ones, the KPg one, is considered to be the result of an impact.)

    3) Mass extinctions. The idea of “sufficiently low” mass extinctions to completely nebulous, and they’ve arbitrarily defined earth’s number as “sufficiently low”. But if the number had been even fewer, there may not have been a KPg extinction at all, and who knows what would have happened then? It took the biosphere about 10 million years to recover pre-extinction levels of diversity after both the PTr and the KPg events, so it seems that the frequency could be as high as one per 20million years, roughly 5 times greater than earth, and still be possibly ok.

    The whole problem with these factors is that they started from the notion that earth’s particular configuration MUST be the ONLY one that can produce complex life and worked backwards from there. Gonzales’ entire contribution to this was the astronomy/cosmology arm of the broader Intelligent Design strategy of the time to insinuate creationist principles into science via stealth.

  115. Amphiox says

    I’m saying none of those lineages necessarily either keeps growing bigger brains or dies out. It may stagnate – whale brains don’t seem to have grown in tens of millions of years, or elephant brains for not quite as long – or presumably reverse the trend; some other lineage will, by sheer chance, take its place. Or not.

    This is true. But my argument is from the point of view of finding an intelligent technological civilization on another planet, and the odds thereof. It doesn’t matter to that argument one bit whether or not an individual lineage increases, stagnates, or regresses in terms of brain size over time. The only thing that matters is who has the biggest/smartest brain in the biosphere at any given time, and what they are capable of doing with that big/smart brain.

    What it essentially boils down to is that a statistical argument pertaining to how intelligence has evolved on earth cannot be applied to determine the probability of finding intelligence on another world, until we find out how those factors we observe that pertain to earth generalize across alien biospheres in general.

    And we don’t know that yet.

    We have to find another independent biosphere for comparison first.

  116. woodsong says

    Amphiox:

    I remember reading a speculative hypothesis that one effect the Moon had was that tides may have helped kickstart life. I’ve also heard (what sounds like plausible speculation to me) that lunar tides may have influenced the colonization of land by various organisms. What’s your opinion on this?

  117. lpetrich says

    David Marjanović in 103 has an interesting argument about agriculture: climate stability over the Holocene, our current interglacial, vs. climate stability over the last 100,000 or so years before. Has anyone tried to test that hypothesis by looking at climate stability over that time?

    This brings to mind the question of the emergence of “behaviorally modern Homo sapiens” (Behavioral modernity – Wikipedia) vs. “anatomically modern Homo sapiens” (Anatomically modern humans – Wikipedia).

    AMHS emerged from “archaic Homo sapiens” species around 200,000 years ago, at the second interglacial before our current one. The emergence of BMHS has been very controversial. A big burst around 50,000 years ago? (the Upper Paleolithic Revolution) Or gradual emergence?

  118. lpetrich says

    So that can explain why the first “modern Homo sapiens” population to move out of Africa did not last long – it was in the Middle East about 100,000 years ago, and Neanderthals later moved in. Could it have been an AMHS population that was not quite BMHS?

    The BMHS ancestors of our present populations came out of Africa around 40,000 – 50,000 years ago, and they were better able to compete with the Neanderthals. That is likely from greater skill at technology, likely resulting in better efficiency in living in cold climates.

    So was it necessary to be BMHS as well as AMHS to invent agriculture? If so, then there was less of a chance of a long period of stable climate like the Holocene during the existence of BMHS.

  119. gravityisjustatheory says

    . Apparently, the % chance a habitable planet develops life is guessed at 13% (I don’t buy it; that life arose so quickly on Earth after its formation suggests that it may be relatively easy — I’d jack that up to something high)

    I used to assume the same thing, until I heard it pointed out that even if life is extremely unlikely, in a galaxy of billions of planets, it can easily occur somewhere early on.

    As an analogy, the in UK National Lottery, any one number selection has a chance of winning just short of 1 in 14 million. Despite that, seven people won in the first draw.

  120. KG says

    The emergence of BMHS has been very controversial. A big burst around 50,000 years ago? (the Upper Paleolithic Revolution) Or gradual emergence? – lpetrich

    Gradual emergence. Discoveries in Africa and the Levant such as those at Qafzeh (burial with grave goods c. 90,000 BP) and Blombos cave (shells pierced for a necklace/bracelet c. 75,000 BP) – both referenced in your first link – evidence in Africa of large scale ochre mining >100,000 BP, bone tools from various sites at >70,000 BP, etc., mean this really isn’t (or shouldn’t be) a live issue any more. The “Upper Paleolithic Revolution” is an artefact of Eurocentrism. For a lot of this see McBrearty and Brooks (2000).

  121. Amphiox says

    I remember reading a speculative hypothesis that one effect the Moon had was that tides may have helped kickstart life. I’ve also heard (what sounds like plausible speculation to me) that lunar tides may have influenced the colonization of land by various organisms. What’s your opinion on this?

    It is an interesting idea. Certainly tidal pools are an interesting environment to consider for abiogenesis for a variety of reasons.

    However, it should not be forgotten that there are also solar tides.

    And in red dwarf systems like Gliese 581, where there are several planets packed tight into resonant orbits, these resonances should also be expected to produce tide-like effects.

    And moons of gas giants, like Europa, and Io, also experience tides (and it is these tides that provide the internal heat for both these worlds that drives their geology, driving volcanism in Io’s case, and melting ice in Europa’s case).

    So you don’t need a large moon to get tides.

  122. Amphiox says

    (Though I would point out that, AFAIK, the tidal flux theories of abiogenesis are currently not the most favored ones)