Sometimes, New Scientist puts a strange twist on their stories — like this one, Universal ancestor of all life on Earth was only half alive. I got stuck on just the title. “Half alive”? What does that mean? It’s describing a paper that did a comparative analysis of genes found in 1800 bacteria and 130 archaea to identify what was common between them, which would suggest what genes were present in the last universal common ancestor.
Now we have the best picture yet of what that ancestor was like and where it lived, thanks to a study that identified 355 genes that it probably possessed.
“It was flabbergasting to us that we found as many as we did,” says William Martin of the University of Dusseldorf in Germany, who led the study. The findings support the idea that the last universal common ancestor (LUCA) lurked in hydrothermal vents where hot water rich in hydrogen, carbon dioxide and minerals emerged from the sea floor.
“It’s spot on with regard to the hydrothermal vent theory,” Martin says. He describes LUCA as half-living, because it may have depended on abiotic reactions in the vents to produce many of the chemicals it needed.
That last bit is where they lost me. I’m about 0.4% salt, which is abiotically derived…does that mean I’m only 99.6% alive? And what about water? I’m 60% water, which means I’m now 39.6% alive, or mostly dead. If you’re just talking about chemical reactions, I don’t have an autonomous power source, but rely on daily input of organic material produced by other living creatures. So by that definition, I am a mostly dead, or undead, zombie PZ that lives by ghoulishly feasting upon the bodies of the living.
When I put it that way, it doesn’t sound so bad.
But I think what is messing us up here is a continuing bias towards vitalism — there is no distinction between “life” and “chemistry”. If you just accept that, we’ll all stop wasting our time trying to figure out what part of our biology is life vs. not-life. This video is a nice simplified approach to the problem of the origin of life, but it also seems hung up on a pointless distinction between “dead chemicals” and “living cells”.
At least the story does make the case for the increasingly dominant hypothesis for the origin of life on earth — that it came from reactions that exploited electron gradients found at deep-sea hydrothermal vents.
One characteristic of almost all living cells is that they pump ions across a membrane to generate an electrochemical gradient, then use that gradient to make the energy-rich molecule ATP. Martin’s results suggest LUCA could not generate such a gradient, but could harness an existing one to make ATP.
That fits in beautifully with the idea that the first life got its energy from the natural gradient between vent water and seawater, and so was bound to these vents. Only later did the ability to generate gradients evolve, allowing life to break away from the vents on at least two occasions – one giving rise to the first archaea, the other to bacteria.
Miracle Max: There’s a big difference between mostly dead and all dead. Mostly dead is slightly alive. With all dead, well, with all dead there’s usually only one thing you can do.
Inigo Montoya: What’s that?
Miracle Max: Go through his clothes and look for loose change.
I read the “half alive” to mean merely that LUCA depended upon an external source for its functioning. (Okay, the sun is also an external source, but that’s not the same thing in context.) Nothing to do with vitalism.
@ #2: But don’t we all? We don’t synthesize sugar from sunlight (would be nice though). I think the question is quite profound, what is life?
ok, but I stopped watching the video about halfway through when it said that their were bags (meaning vesicles of membranes) floating around, and these could internalize other molecules. Gah. Not hydrothermal venty enough for me.
dick@2: we depend on a 20% O2 atmosphere at about 100 kPa and about 300K. We die within minutes when we deviate too far from that. Are we really that different from organisms that rely on H2S dissolved in salt water at about 350K under a few MPa of pressure?
My guess is that Martin meant that LUCA could make use of a proton gradient across a membrane, but could not generate one, and New Scientist have garbled what he said. He (and Nick Lane, also mentioned in the article) regard these two (gradient-producing and gradient-using) processes as the most fundamental features of life, so an organism with only one of them is “half-alive”. I’ve just started reading Lane’s The Vital Question – I’ll see if that throws any more light.
I read the “half alive” to mean merely that LUCA depended upon an external source for its functioning
So does Dick Cheney.
As to water PZ, we could technically think of much of it as biotically derived, since many reactions in our bodies utilize hydrolysis and dehydration. Technically speaking, we synthesize and break down water molecules constantly.
Not that that makes the distinction any clearer.
If I’m not mistaken, pretty much all of earth’s energy comes from the sun.
If you listen to some Christians, anybody who doesn’t follow their brand is already dead and worthless, so according to them, we ARE the walking dead.
“a pointless distinction between “dead chemicals” and “living cells”.”
Is it possible to ‘kill’ a cell without changing the constituent chemicals? If so, what exactly has been done?
Gmacs, geothermal energy is independent of the sun. It’s left over heat from the formation of the Earth, and from atomic decay in the core.
It would be interesting if we hairless apes had some sort of organelle in our skin that functioned like chloroplasts. When a bit low on glucose, one could just sit in the sun for a short time enjoying some mineral water. My question is, which cells of the skin would be best suited to house these organelles?
I’ve seen a few papers suggest that eubacteria are not monophyletic, with archaea instead close to Gram-positive bacteria – like clostridia. I wonder if that’s really been settled, or if this CA is only being assumed to be LU.
Artor@11: “Gmacs, geothermal energy is independent of the sun. It’s left over heat from the formation of the Earth, and from atomic decay in the core.”
But the formation of the Earth was the result of the formation of the Sun, or perhaps more correctly the same process that formed the Sun also formed the Earth and all the other things that orbit our Sun. We all came from the same interstellar cloud compressed by gravity. No Sun, no Earth.
Anyway the insistence that must be some clear definite boundary between “living” and “dead” strikes me as merely another instance of the continuum fallacy.
Amphioxus – I think you meant Vitamin D.
@PZ
To be fair, your detractors have been saying that for years.
Water is amazing stuff. It changes from solid to liquid to gas, here on this planet, and each form exhibits shapes and responses to the rest of the world that boggle the mind. Snowflakes, glaciers, wind waves, standing waves, clouds, frost crystals – absolutely incredible. And, as you say, hydrothermal vents.
And then we drink that water, and we never let it freeze and we never let it boil, and we never dissolve anything really interesting in it, and we never let it respond to the pull of the moon, and we call ourselves alive, and we say that water was lifeless before we captured it and contaminated it and pissed it away.
#10, corwyn:
Mechanical damage would do the job, right? Once the cell membrane is breached, all those nice chemical gradients aren’t going to hang around for long.
#12, kesci
The problem is one of surface area and efficiency. More stuff here: https://what-if.xkcd.com/17/
@19:
“Mechanical damage would do the job, right? Once the cell membrane is breached, all those nice chemical gradients aren’t going to hang around for long.
In which case they are no long constituent.
Rephrasing, is it possible for a cell to be not alive, while still having all the requirements? Or is there a way to stop (permanently) the chemical processes without starving them?
Thank you kindly.