Earlier this month, there was a flurry of headlines in the pop-sci press that exasperated me. “Have scientists discovered reversible evolution?” was one; “Evidence of Reverse Evolution Seen in Dust Mites” was another. They failed because they always tried to express a subtle idea in a fluffy way that screwed up a more fundamental concept in evolution — it was one step forward in trying to explain a legitimate science paper, and ten steps back in undermining understanding of evolution. This was just awful:
Researchers who deny the idea that evolutionary traffic can only move forward saw their arguments bolstered this week with the publication of a study suggesting that house dust mites may have evolved from free-living creatures into full-time parasites, only to abandon that evolutionary track and go back the way they came, reverting to the free-living creatures that live invisibly in your carpet, bed, and other places in your home that it’s probably best not to think about them living.
“Evolutionary traffic can only move forward”? Please, define “forward” in this context for me. Evolution doesn’t have a direction. You can talk about a temporal sequence of historical changes in a gene, for instance, but from the point of view of the process, there’s no “forward” or “backwards”, only change over time. Is a genetic deletion a backwards step? Is a duplication a forward step? If a mutation changes a cytosine to an adenine, is that going forward, and if there is a revertant, a mutation that changes that adenine back to a cytosine, is that going backwards? I keep hearing this talk about directions, and it doesn’t even fit into my understanding of the process of evolution. Direction is always something people infer retrospectively.
The paper all this comes from, Is Permanent Parasitism Reversible?–Critical Evidence from Early Evolution of House Dust Mites, by Klimov and O’Connor, isn’t that bad, but still it has some bits that annoy me.
Long-term specialization may limit the ability of a species to respond to new environmental conditions and lead to a higher likelihood of extinction. For permanent parasites and other symbionts, the most intriguing question is whether these organisms can return to a free-living lifestyle and, thus, escape an evolutionary “dead end.” This question is directly related to Dollo’s law, which stipulates that a complex trait (such as being free living vs. parasitic) cannot re-evolve again in the same form. Here, we present conclusive evidence that house dust mites, a group of medically important free-living organisms, evolved from permanent parasites of warm-blooded vertebrates. A robust, multigene topology (315 taxa, 8942 nt), ancestral character state reconstruction, and a test for irreversible evolution (Dollo’s law) demonstrate that house dust mites have abandoned a parasitic lifestyle, secondarily becoming free living, and then speciated in several habitats. Hence, as exemplified by this model system, highly specialized permanent parasites may drastically de-specialize to the extent of becoming free living and, thus escape from dead-end evolution. Our phylogenetic and historical ecological framework explains the limited cross-reactivity between allergens from the house dust mites and “storage” mites and the ability of the dust mites to inhibit host immune responses. It also provides insights into how ancestral features related to parasitism (frequent ancestral shifts to unrelated hosts, tolerance to lower humidity, and pre-existing enzymes targeting skin and keratinous materials) played a major role in reversal to the free-living state. We propose that parasitic ancestors of pyroglyphids shifted to nests of vertebrates. Later the nest-inhabiting pyroglyphids expanded into human dwellings to become a major source of allergens.
It’s actually rather interesting that these mites have a phylogenetic history that shows some dramatic changes in lifestyle. Parasitism is a specialized pattern that typically involves a loss of shedding of generalized abilities that allow for autonomous living; they can get rid of functions that won’t be needed in the conditions they’ll be living in. A mammalian parasite is swimming in a sea of nutrients provided by the host; it can lose genes for the synthesis of many amino acids, for instance, and still survive because it’s immersed in those amino acids, provided by the mammalian bloodstream. But that makes it difficult to leave the parasitic life — if it moves out to the more limited diet available in the external world, it may find itself starving to death, unable to synthesize essential building blocks. Yet here they have evidence that mites shifted from parasitism to free-living.
But I have two complaints. One is this framing as a refutation of Dollo’s Law — I really don’t give a damn about Dollo’s “Law” at all. The second is that they haven’t really shown any evidence of molecular/genetic reversibility.
I just roll my eyes at papers that talk about Dollo’s Law anymore. Do people realize that it was a macroevolutionary hypothesis formulated in the 1890s, before anyone had a clue about how genetics worked, much less how genetics and evolution worked together? It was a reasonable prediction about how traits would distribute over time. A horse, for instance, runs on a single robust toe on each leg, the other digits reduced to vestigial splints; Dollo’s law says that those splints won’t re-expand to reform toes identical to those found in horse ancestors. Why, he didn’t know.
A modern understanding of the principle, informed by the underlying genetics, would instead say that a complex character involving multiple genetic changes and relying on a particular background for its expression is statistically unlikely to be reconstituted by stochastic changes in a different genetic background, in exactly the same way. It’s not a ‘law’, it’s a consequence of probability.
The authors have only found reversion to an ancestral pattern on a very coarse scale: there are a great many ways to be a free-living organism, and there are a great many ways to be a parasite. They can say on a very gross level that mites have changed their niches in their evolutionary history, but they can’t claim there has been an evolutionary reversal: if we compared the ancestral free-living form (pre-parasite phase) to the modern free-living form (post-parasite phase), I have no doubt, and there’s nothing in the paper to contradict me, that there would be significant differences in form, physiology, biochemistry and genome, and further, that the parasitic phase would have left evolutionary scars in that genome.
Dollo’s Law is archaic and superficial, and I have no problem agreeing that Klimov and O’Connor have refuted it. But the more interesting principle, founded in a modern understanding of microevolutionary and genetic events, has not been refuted at all — it’s just confusing that we’re still calling that Dollo’s Law, and that we mislead further by talking about a direction for evolution and ‘reversibility’ and all that nonsense. The only source of direction in this process is time’s arrow, and that doesn’t go backwards.
This is what Theodosius Dobzhansky, perhaps the central figure in the Evolutionary Synthesis, had to say about irreversibility in “Genetics and the Evolutionary Process” (1970): “The evolution of every phyletic line yields a novelty that never existed before and is a unique, unrepeatable, and irreversible proceeding…. “! Dollo’s law was formulated before Mendelian genetics came along and seems to reflect a metaphysics of universal progress absent in Darwin. Dobzhansky seems also to have been infected by woo, but it cannot be denied that cumulative base pair changes in DNA, etc., over time will after not too many generations make it essentially impossible for genotypes identical to those of ancestors to again come into existence. Dollo’s Law from the revisionary viewpoint of molecular population genetics is correct.
As to Dobzhansky’s views, consider another quote from the same book: “[N]atural selection has tried out an immense number of possibilities and has discovered many wonderful ones. Among which, to date, the most wonderful is man.”
Reverse evolution can be refuted using an example of evolution that we have all come to know and love. When smog occurred as a result of the start of the British industrial revolution peppered moths evolved a dark coloration that allowed them to better blend into their soot ridden environment and now that Britain has cleaned up their environment the moths have returned to their light coloration. Are we to believe that this is an example of reverse evolution? Even a creationist should know better than to believe that.
a-HA!!! See? Another so-called “Law” of “Science” revealed to be just another theory. Take that, eggheads!
But, yeah, Dollo’s is a stupid straw-Law to hang your hype on. Far worse, to me, is the lack of any feeling for the organisms.
The fuck makes this a useful “model system”? Hype, hype, hype. So stupid.
Look, the putative parasitic progenitors of today’s dust mites were NOT endoparasites, “immersed in…amino acids, provided by the mammalian bloodstream”. They werwe ectoparasites, like today’s feather mites and eyelash mites. They lived not inside but on the surface of their hosts, eating scraps of keratin. Moving that lifestyle to nests and then to dustbunnies was simply not that big a deal: to a mite, it’s still an umimaginably huge world with bits of keratin here and there. What do they care?
In other words, in this case, parasitism is simply not a very complex trait at all.
Even the fucking title is just stupid: “Is Permanent Parasitism Reversible?”
um, no, by definition of both ‘permanent’ and ‘reversible’.
I don’t doubt that the data and analysis are first-rate, and I think there’;s an interesting story here about mites specifically, but jeez-o-weez, these results have been overhyped almost to the point of parody, and this time not just in the press release. Pises me off.
How much of this is just the usual misunderstandings of evolution, the apparently common belief that evolution is a one-way road, always pointing towards a ‘higher’ form of life? And, of course, the very highest form of life is, well, ME!
There was a caller on the Atheist Experience show this week, an admitted Catholic, who obviously felt just this way about human evolution. Oh, he believed in evolution, of course, because the Church believes in evolution (sort of), but according to this caller the different races of humans didn’t evolve at the same rate! The show’s hosts tried to explain it, though I think they were being a bit soft on him. But it was obvious that the caller believed that HIS race was at the very pinnacle of evolution, and all of those other races were lagging far behind. I don’t think he would have been able to even come close to a true understanding of the working of evolution.
Even the abstract stipulates the contribution of the history of the lineage. Their diet as ectoparasites gave them an exaptation in the form of enzymes for breaking down keratin.
I was channeling PZ’s refutation of this article on “reverse” evolution and Dollo’s so-called “law” as I was reading it a couple of days ago. I was fairly spot on, I appreciate the elucidation that the actual PZ presented in his post and now have a net increase in my understanding of evolutionary process. Thanks.
Hear hear!
I’ll be interested to read the paper. if much hinges on ancestral-trait reconstruction, especially in a group where they indicate short-walks to extinction are likely, then they are already playing with dubious and highly unreliable data, even before any misinterpretation.
Change is related to environment and the need to adapt, right? Didn’t the dust mites adapt in one environment? And when the environment changed, the adaptation was dropped by natural selection? That hardly sounds like “going backwards”. It sounds more like me selling a used car that I don’t need.
Humans have domesticated and artificially selected many wild animals (e.g. dogs, cows, pigs, pigeons, etc.). If they were left to roam wild for thousands of years, would the traits we selected eventually disappear because they are not (and never were) needed for survival, and the animals revert to their natural forms?
Horses were introduced to North America five hundred years ago, and herds have lived in the wild for 200 years. According this NatGeo item I found, wild horses have shrunk in average size because humans aren’t breeding for size and speed. Traits that were artificially selected are starting to vanish.
http://news.nationalgeographic.com/news/2001/10/1024_TVmustangs.html
Is that “evolution going backwards”? I doubt it. It sounds more like the horses are adapting to their environment, the same as the dust mites.
Yeah, on my 25th birthday I bought a car. After having owned it for ten years I sold it again, so now I’m back to being 24 years old. So obvious, duh.
From wikipedia:
The physicist’s POV: Well, yeah, evolution is irreversible. Everything is.
It’s that simple, really. Whales aren’t fish. Birds aren’t pterosaurs. History leaves traces.
So much for what Dollo said. But, here’s what the implications are:
If a living organism was the product of design, it would be possible to have a clean slate. It would be possible for a designer to re-introduce a previously implemented “vintage model” into an environment that had reverted to a previously favorable state. (Environments can more easily revert to almost the same conditions, as they are far simpler than living organisms).
But, as there are no blueprints of organisms, as the body plans are only preserved within living, breathing bodies, this cannot happen. Previous design is lost, and all further modifications depend on what has already happened.
In other words, Dollo’s law is a good test of naturalism. Creationists sort of realize it, which is why they would like it disproved. It’s a good thing, then, that it still holds.
Dollo’s Law has recently been invoked in the birds-are-dinosaurs, are-not, are-so controversy. Typical theropods have shorter arms than birds do, and also shorter ones than typical “thecodonts”. Clearly it’s evolutionarily impossible for arms to shorten and then re-lengthen. Dollo’s Law! Therefore, birds aren’t dinosaurs.
I see how this line of reasoning ‘bolsters’ the arguments of the brave researchers that ‘deny the idea that evolutionary traffic can only move forward’ but I’m more interested in who are the ‘Forwardians’ that have been advancing their ‘Forward Only’ agenda at the expense of our brave ‘Back-and-Forth’ protagonists?
What does the leading advocate of Big Forward have to say now that the leaders of the Evolutionary Directional Liberation Front (EDLF) have come forward with this groundbreaking research?
Practically speaking, I know next to nothing about the mechanics of evolution. I do know enough, however, to have grasped the one basic necessary principle that needs knowing before understanding anything else about it- evolution is a process only that is not frickin’ normative; there are outcomes only, no aims. So changes over time aren’t changes in direction, they’re only changes. I think it’s an instinct in any normative mind that relies for its survival on establishing and pursuing goals to see normative features in processes that have none; but that’s a burden that needs to be discarded, not clung to.
Unless you consider the fact that environments comprise, among other things, living organisms. ;)
@Thorne, @thisisaturingtest: I’ve no data, only a suspicion. But I suspect that if one’s mind is so starved for purpose and teleology in the universe that you can unblinkingly accept a magic sky dude…evolution MUST have a purpose! Because otherwise stuff wouldn’t occur for reasons, it would all just be random, and that’s so scary I can’t take it!
Memo to the everything-has-a-purpose crowd: I have discovered the essential nature of the universe, and I’m willing to share it with you. Ready?
Shit happens.
Some of it happens to organisms with heritable characteristics. Some to organisms with consciousness.
Deal.
But, but, humans are the bestest thing evolution ever made!!!!!11!!11!!! Of course evolution has a direction – from goo to MEEEEEE!!!!!
Shoot, Thorne beat me to it and I didn’t see it!
I was kind of expecting that one. (It is, after all, the main point of Dawkins’ The Extended Phenotype, a book I absolutely loved)
We can mean different things by saying “environment”. One meaning is “climate”, where we are interested in such things as temperature and humidity, which can easily revert after a relatively short time (or, much quicker, if the organism migrates). Another meaning is “ecosystem”, which I would agree cannot, for all practical purposes, revert.
Since we were discussing parasites, obviously their evolution is bound with the evolution of their hosts. But, I can easily imagine a former parasite “magically” reverting to exactly its former free-living form and still being pretty well adapted to its environment. In fact, I suspect there must be cases of species that have bifurcated, where one branch became a parasite and another continued to evolve as a free-living organism.
Indeed, this almost certainly happened with each and every independent evolutionary origin of parasitism.
And there have beem very many of these. (There are highly specialized endoparasitic barnacles and jellyfish ffs.)
Everybody should read Parasite Rex, by Carl Zimmer!
If I may correct myself: Just learned that ‘permanent’ is a term of art in parasitology, whereas I obviously applied the vernacular instead. oops.
to wit:
or, I guess, on them.
By direction I would have thought that it would be the path that leads to greater fitness at that particular time and place in the fitness landscape. Of course this is not a static thing as the fitness landscape continually changes.
The only source of direction in this process is time’s arrow, and that doesn’t go backwards.
I don’t know if that idea was stated by Darwin directly but I’m pretty sure it was implied. It needs to be emphasized generally it also true for all the “results” from “the big bang”.
higher forms and lower forms and ideas like purpose are a conveniences of language only, and are misleading.
What is the purpose of a dust mite? What is the purpose of hack journalists? Who is more “highly evolved” you or me ?
Why of course the answer is clear!
uncle frogy
It has always seemed to me that “law” means something entirely different to biologists than it does to chemists and physicists. To the latter, it is a description of how two or more phenomena are related. In biology, it seems to be more like a rule of thumb, or like some general kind of expectation.
Oh. We biologists also have a central dogma. In your face, dogma-free scientists.
I grew suspicious the second I saw “forward Evolution”. This sounds like one of those vague concepts like “Higher Evolution”, like some animals are more “Highly Evolved” than others. It’s all predicated on the idea that some animals are somehow “better” than others, and that evolution is a sort of path to “betterness”. In short it’s a crock and it annoys me.
This is similar. “It’s going backwards? How can it go backwards?”. It’s not going backwards, it’s just going. Something changed that meant their current physiology or lifestyle wasn’t optimal any more. So it changed. That’s it.
Isn’t that kind of like saying that the evolution of turtles went backwards because they went from water to land to water???
I should also note that the model of nucleotide evolution most often selected in phylogenetic analysis is called the General Time-Reversible model.
In your face, Dollo.
In real life of course it doesn’t, but we could give a solid enough definition of evolution “going backwards”. It would simply mean “retracing its genetic history”, i.e., all mutations are exactly reversed in order.
I’m thinking Dawkins’ biomorphs. It’s simple enough to imagine a “lineage” of biomorph creatures reversed, and if the program was automated somehow (I mean, if progeny was not selected artificially by the user, but by some complex “fitness function”), I’d bet against any sufficiently long sequence repeating itself before the universe ended.
For real animals, of course, things are complicated by developmental processes and sexual reproduction (sex always complicates things, in my experience ;-) I very much doubt if reversing the mutations would be enough to exactly reverse the developmental environment shaped by them in the past.
Yeah. Phylogeneticists haven’t accepted Dollo’s “law” ever since their discipline became a science (which was scarily recently).
Recently? Are you sure you’re not talking about the early 1980s at the very latest?
(Or has Feduccia reverted to the early 1980s? Frankly wouldn’t surprise me.)
http://www.vaderno.com/
And then the tortoises came to land again!
The way I understood it, Dollo’s “law” is just statistical.
At any given time there are countless possible directions in which evolution can go. Precisely backwards is just one of them. So what is the chance that it will be the one you actually observe? Asymptote to zero.
Of course, it is actually just a special case of the bigger truth about evolution – ie that it has no predefinable directionality.
In the case of Dollo’s Law, the outside observer predefines a direction (ie, “backward”), looks to see if it can happen, and sees that it does not. But the observer can define any arbitrary direction he or she wants to, and on looking, will have the same infinitesimally small chance of observing it happen.
“Dollo’s Law? That’s so Nineteenth Century!” This is very bad science writing.
When we’re talking about mites that live on fur or feathers evolving to live on fallen hairs and in feather pillowcases, it doesn’t seem like such a stretch. But it’s no more “going backwards” than lungfish to hoofed mammals to whales was.
To cheer you up, I have fluorescent embryonic zebra-fish brains.
Fun thing is, Dollo didn’t have simple irreversibility in mind. He thought that “complex” character states may be secondarily lost often, but can only gained a total of once, so all organisms where you find such a state must have inherited it from a common ancestor. This is why the never-used “Dollo” setting in programs for phylogenetic analysis is distinct from the “irreversible” setting.
What you quoted from the paper hints as much:
I read it to imply that the modern free-living form is dependent on features that were aquired during the parasitic phase and thus would be a different form of free-living from the ancestral free-living form.
Don’t worry about it. I’ll send an email to instruct you where to send the royalties. About $500K should cover it, don’t you think?
wbenson:
I am far from being any kind of evolutionary scientist, but the flaw in this idea of evolution of this sort being evolution ‘reversing itself’ is blindingly apparent to me. It’s like saying that, because the road you’re driving along goes around a 180 degree hairpin bend, you’re actually now driving in reverse gear.
When I get people asking me questions about evolution where they start wondering about directionality, I always respond with:
which is forward: a triangle or a circle?
corollary…
some (who fail maths) respond with:
“The triangle is more complex because angles!”
so then I show them a rubber band…
That is also why organisms don’t necessarily “progress” when conditions aren’t changing. The forces of selection push them back towards their currently adapted state.
I would add to that though. While it defines the theoretical nature of evolution well enough, it of course is not an accurate description of how it works in practice. If we have a good guess as to what the primary selective factors are for a specific trait, we can in fact make a probabilistic estimate of which directions the trait will evolve. Moreover, it ignores existing constraints on the system (both genetic and developmental), which, even if you’re just considering drift, still apply.
When I drive to the grocery store, I go forward. As Dollo’s law states, since we wind up at the same place at the end, I must have gotten home by driving the whole way in reverse.
Oh, wait.
you know, this whole paper reminds me of the story of the Midwife Toad*.
developmental plasticity, anyone?
*in fact Attenborough did a very nice summary of this story just recently. It was in one of his “natural curiosities” episodes: http://eden.uktv.co.uk/shows/david-attenboroughs-natural-curiosities/
also a great book: “The Case of the Midwife Toad”
oh, I guess a quick summary:
the toad can switch breeding modes from entirely land based to entirely water based, depending on environmental conditions, and a great but in the end confounded biologist by the name of Paul Kammerermanaged to convince himself this was a case of Lamarckism, thus Darwin was wrong.
oh, and before you ask… Yes, creationists have indeed at various points tried to use Kammerer as both an example of how “Darwinism has teh fail!” as well as an example of “Expelled!”.
and if you wonder why you’ve never heard of it before… well, it’s because no matter how you look at it, it was a failure. Though it is an interesting story nonetheless.
Not so much ignoring it as making the assumption that even after applying all knowable constraints, there will still be a wide range of possible outcomes to choose from.
But yeah, in theory if we knew the developmental restraints well enough we could in theory narrow down the possibilities sufficiently to make a probabilistic estimate that is high enough to be meaningful, if we can also be confident that the selective pressures entertained will remain constant for a sufficient period of time.
But in real life that last bit might prove the hardest of all, outside of controlled experimental scenarios.
IIRC, in Lenski’s experiments he observed parallel evolution of a number of traits that repeated in the different bacterial lines (things like increased cell size and the like), and frequently found on analysis of the genomes that often the same genes mutated to produce the trait in all the examples, and sometimes even the same nucleotides were changed.
that’s actually been done, many times.
Read John Endler’s work on guppies, and work your way up via the science citation index from there, just to follow one tiny thread of it.
David Marjanovic:
There is no surprise. He invokes Dollo in his new book Riddle of the Feathered Dragons.
So, it should have gone to a Journal of Negative Results :-)
Ah. That came out last year. Still, he should be deeply embarrassed. :-)
wow. If I was an author, I would be really insulted.
Kammerer was evidently a fraud, and Koestler (author of the ‘great book’ about him) an anti-Darwinist propagandist.
I just read the English and the German Wikipedia article on Paul Kammerer. Hoo boy. Kammerer… had a couple of problems, shall we say. Was in love with Alma Mahler and threatened several times to shoot himself on the grave of her husband, on whom he had had a massive man-crush, if she wouldn’t love him back. *facepalm* She later said, quotes the article, that he wished the results of his experiments into existence “so glowingly that he was capable of unconsciously deviating from the truth”…
Doesn’t mean he himself committed the forgery or even knew about it. Plenty of people had all kinds of motives. The amount of political ideology that surrounded the controversy of Lamarck vs. Darwin in those times is deeply sickening.
At some point I’ll translate stuff from the German article to add to the English one.
no, he wasn’t.
you took the superficial view of what happened without looking further.
fail.
yes, he did, but it doesn’t take away from the fact that he was one of the most productive biologists of his day.
He was wrong about the midwife toad, but that doesn’t mean he was a fucking insane idiot FFS.
what is wrong with you folks?
In terms of numbers of papers with his name on it, do you know who’s the most productive vertebrate paleontologist of this day? I want to avoid mentioning his name.