Tuesday, July 21, 2009

Direction and Purpose in Evolution

 
If you put two people together who believe that natural selection is the only important mechanism of evolution and that humans are the only, and best, end product of evolution, then this is what you get.

Watch Robert Wright and Daniel Dennet discuss direction and purpose in evolution.


Now imagine what the discussion would look like if they really understood the important role of chance and accident in evolution and, instead of humans, they used lobsters, ginkgo trees, shiitake mushrooms, rotifers, and cyanobacteria as examples of modern evolved species with three billion years worth of ancestors.

Even worse, think about the octopus. Is there any sane person who would point to the existence of those eight-legged slimeballs as evidence that evolution must have a direction and a purpose?


[Hat Tip: Robert Wright]

23 comments :

  1. While I do like a lot of what he's written in Darwin's Dangerous Idea, the chapters of intentionality and directionality of evolution really REALLY bugged me. Also, he completely and utterly butchers microbial evolution, but perhaps that's a little too much to expect from a non-biologist.

    There's a great way to view evolution of complexity; don't know if you've heard of it, but Constructive Neutral Evolution (eg. as discussed in Stoltzfus 1999 J Mol Evol): say you start out with a one component system - let's call it A. Say A is essential for the organism's survival, and is thereby highly conserved.

    Now, say there's another unrelated component, B, that just happens to improve/stabilise A's performance. In this case, A can still function without B, so it's still strictly a one component system. But now, A can degrade where B complements its function. Once this happens, B becomes an essential component for its function, and suddenly we come to a two component system. This system doesn't have to be any more fit than the single component version; the net result is neutral. But an increase in complexity has occurred.

    (there's a good real example involving a N.crassa mitochondrial CYT18 self-splicing intron - Collins & Lambowitz 1985))

    After a bit of digestion, it's becoming more and more apparent that this process may actually be quite prominent in evolution. It includes/powers things like neo- and subfunctionalisation, which is essentially what happens on the cellular level in multicellular organisms.

    After a while, you actually begin to see animals as extremely un-streamlined versions of bacteria!

    In light of this view (which is quite ignored by animal biologists, it seems), Dennett's anthropocentric obsession with intentionality and purpose is painful to watch. Of course, he gets his evolutionary biology from the loud, popular sources - ie animal population biologists (who tend to have a rather warped view of how genes actually work, grrr)

    It's also another popular fallacy to assume natural selection is about the survival of the fittest, which encourages a very directionalistic view. I heard a better way to put it: "the survival of the barely tolerable".


    Actually, I'll argue Warnowiid dinoflagellates are actually the higher eukaryotes. You can't really beat a subcellular image-forming camera eye... =D

    -Psi-

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  2. "Is there any sane person who would point to the existence of those eight-legged slimeballs as evidence that evolution must have a direction and a purpose?"

    http://scienceblogs.com/pharyngula/

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  3. That was actually quite painful to watch-- I'd never have imagined Dennett rolling over with so many "sure"s in agreement that natural selection acts in some sort of directed fashion. When he wasn't being badgered into conceding some minor and semantic point, Dennett manages to muster a rather defensible position re: evolution, but for the most part he seems willing to be brow-beaten into submission to the twittish questioner's blind alleys.

    Is intelligence a predictable outcome of evolutionary processes? Yes, given enough trials.

    Would the evolution of intelligent life (forms capable of predicting future events based on stored memory and analysis of past experience)be a game-breaker? You betcha!

    Was the evolution of intelligent life forms an inevitable outcome of the emergence of life on earth? Hardly.

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  4. Well, would direction of filling and refining to available niches count as direction?

    That's the only sense in which I can imagine natural selection having a "direction". It is a messy word though.

    To me this sort of conveys the difference in ability people can have in live debate vs. written argumentation. I recall absolutely wincing during a interview/debate Richard Dawkins had with Ted Haggard.

    But yeah, Dennett should maybe stick to writing complicated metaphysics books to continue torturing us philosophy students >.<

    (Btw, do I sense something personal against octopuses? ;)

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  6. The whole problem with people misunderstanding how evolution works is a product of insufficient education. How many departments require their biology/molecular biology/biochemistry/etc. students to take even a basic course in population genetics? Very few. And the people who ever get exposed to the issues of genome evolution and the forces that shape it are a small subset of those.

    Then it is not at all surprising that people get it all wrong, especially basic facts like the one that the smaller the effective population size, (which is roughly inversely equivalent to the size of the organism) the bigger role chance plays in the evolution of that species. This makes it very hard to believe that something like human intelligence was inevitable, unless you go irreversibly in creationists la-la land by postulating divine interventions on the quantum level like Francis Collins and Ken Miller. But most people just don't know/ don't think about it...

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  7. Bad journalism, in my opinion. Questions are way too long and meandering, and aswers are "pull out of the mouth", without the interviewee thinking too much about them.
    Not a good job.

    Marco Ferrari

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  8. Georgi Marinov says,

    Then it is not at all surprising that people get it all wrong, especially basic facts like the one that the smaller the effective population size, (which is roughly inversely equivalent to the size of the organism) the bigger role chance plays in the evolution of that species.

    It's a little more complicated than that but I agree with you that most people don't understand evolution very well.

    Small populations are subject to many sorts of chance and accident that large populations are largely buffered from experiencing.

    However, the rate of fixation of neutral alleles isn't one of them That's largely independent of population size.

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  9. Then it is not at all surprising that people get it all wrong, especially basic facts like the one that the smaller the effective population size, (which is roughly inversely equivalent to the size of the organism) the bigger role chance plays in the evolution of that species.

    I think we still haven't come to terms with understanding how selection acts at the level of total fitness. Most models of evolution, be they theoretical or empirical (i.e., testing for evidence of selection in genomic data) still rely on finding patterns in single genes. It's only recently, with things like re-sequencing and polymorphism data, that we're starting to think about what gets 'dragged along for the ride' in terms of genomic regions, or how processes like Muller's Ratchet affect diversity and adaptation. The idea that evolution can optimize all of these particular parameters at once, as many of these people seem to argue implicitly, is wishful thinking.

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  10. Larry Said...



    Small populations are subject to many sorts of chance and accident that large populations are largely buffered from experiencing.

    However, the rate of fixation of neutral alleles isn't one of them That's largely independent of population size.


    Correct me if I am wrong but this isn't true. Effective population size is a key parameter in the formulae for the probability of fixation/loss of neutral alleles under genetic drift at any given generation as well as for predicting the number of generations for fixation/loss to occur.

    Because drift is essentially sampling error it will always be stronger/more prominent in populations with a lower effective population size.

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  11. Marco F. says,

    Bad journalism, in my opinion.

    It's not really an interview in the journalistic sense. Robert Wright has a well-known agenda. The video is more like a debate than an interview and I think Daniel Dennett realizes this.

    Remember, this is "bloggingheads," which Wright founded.

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  12. Larry: "It's a little more complicated than that ..."

    Yes, the additional complication arises when you consider mutations that are nearly (but not quite) neutral. Smaller populations are more likely to 1) fix "weakly deleterious" alleles and 2) eliminate "weakly beneficial" alleles, compared to larger populations.

    DG: "Correct me if I am wrong but this isn't true. Effective population size is a key parameter in the formulae for the probability of fixation/loss of neutral alleles under genetic drift at any given generation as well as for predicting the number of generations for fixation/loss to occur."

    You are correct as far as you go, but larger populations are more likely to generate neutral mutations. So, with respect to the accumulation of neutral mutations, population size balances out exactly (in theory): rate of generation is proportional to N, rate of fixation is proportional to 1/N.

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  13. Divalent said..


    You are correct as far as you go, but larger populations are more likely to generate neutral mutations. So, with respect to the accumulation of neutral mutations, population size balances out exactly (in theory): rate of generation is proportional to N, rate of fixation is proportional to 1/N.


    The rate of fixation is proportional to 1/Ne, is the rate of generation proportional to N or Ne?

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  14. How easy it is for philosophers to make some statements that actual scientists would never make...both these philsophers seem to agree that complexity in development arises by natural selection...
    No true developmental biologist I know seriously thinks this way. It may be prettty and comforting to do so but it is actually clearly an insufficient expalantion of development.

    Natural selection is also insufficient to explain complexity iin evolution. Many other factors and mechansism other than selection egenrate complexity, both in development and evolution. The discussion of these people is thwarted by theirt obsession of adressing the arguments of natural theology. Dennet is bound to lose: he's playing the game by the rules of the enemy.

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  15. Small populations are subject to many sorts of chance and accident that large populations are largely buffered from experiencing.

    However, the rate of fixation of neutral alleles isn't one of them That's largely independent of population size.


    That's why I very carefully worded it as "the smaller the, Ne, the bigger role chance plays", and not mentioned the more complicated issues of rate and probability of fixation.

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  16. It's not really an interview in the journalistic sense. Robert Wright has a well-known agenda. The video is more like a debate than an interview and I think Daniel Dennett realizes this.

    Now I get it. So why did Dennett accept it in the first place (did he know Wright's agenda?), and why the answers were so insecure? You know, I'm from the land of the buffoon PM, we have already some kind of censorship (kidding, of course)

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  17. I like "survival of the barely tolerable". Other candidates:

    * "survival because it can"

    * "survival of the half-assed"

    * "survival of the survivors"

    The point is that "beautiful" examples of evolution are the exception rather than the rule (e.g. intelligent design vs. intolerable design).

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  18. Mr Vargas comments:

    "Natural selection is also insufficient to explain complexity iin evolution. Many other factors and mechansism other than selection egenrate complexity, both in development and evolution."

    What alternative mechanisms do you propose for the evolution of complexity? I agree with you by the way, but I want your take.

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  19. symbiosis and other forms of associations of organisms (for example, intra-specific sociality) is one readily understandable form of increasing complexity in evolution.

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  20. @Ford
    What alternative mechanisms do you propose for the evolution of complexity? I agree with you by the way, but I want your take.

    The way I see it (which is probably rather worthless but shhh) is that there's mechanisms generating "new" traits/features (via modification of stuff) eg: mutations, symbioses, generation of excess capacity in the aforementioned constructive neutral evolution idea; and then there's the 'pruning' mechanism(s), ie natural selection and physical constraints (and chance, to some extent). The interactions of the two mechanism categories result in phenomena like ratchets, neo/subfunctionalisation, constr neutral evol etc. But selection alone is insufficient for anything to happen. You need to generate stuff to be subject to selection in the first place...

    God that was an awful paragraph... did that make ANY sense? I can clarify -after- my final exam if necessary...

    -Psi-

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  21. PS: I think problems arise from focusing only the population biology aspect of a very small and insignificant fraction of life (metazoa). It turns out that sex is neither necessary nor [arguably] all that important in evolution; there's also a whole assortment of molecular processes that are actually important in evol, especially for the synthesis of 'new' features.

    And evolutionary biol seems to not be required for biology degrees in many places... that makes no sense! Evolution is CENTRAL to biology (and this is coming from a cell, not evolutionary, biologist) and so many people misunderstand it. Unlike physics, where people readily acknowledge their weak grasp of the subject, evolutionary theory is viewed as something simple and therefore often completely butchered, even by professionals.

    Eg. I mentioned to a zoology prof once that I intend to work on protists in the future... the response: "OH, the -primitive- eukaryotes!" "...no."

    And then another guy (also full prof): [implies fungi-animals-plants is a natural class of some sort] me:"Actually, fungi, animals and plants gained multicellularity independently, which also arose upwards of 16x in eukarya and at least once in prokaryotes, and are actually not sister groups to each other etc etc etc" Response: "Why should I care? As far as I'm concerned, fungi, plants and animals are once group. I'm a cell biologist." GRRRRRR.

    /rant

    Oh shit, I'm late to stuff...

    -Psi-

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  22. DG: "The rate of fixation is proportional to 1/Ne, is the rate of generation proportional to N or Ne?"

    Effectively (for this purpose), Ne. For example, an individual who happens to be sterile and who inherited a neutral mutant allele would be counted as part of the N (and his allele would factor into determining the overall population frequency), but would not be part of Ne.

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