Convergence

We are cluttering up a thread that’s not about convergence with discussions about convergence. Here, we can discuss this specific issue.

Convergence, or homoplasy, occurs when two individuals share a feature that is not inherited from their (assumed) common ancestor. Such a feature may be a phenotype – for example, sharp teeth in many predators, streamlining in fast swimmers, wings in diverse groups – or a genotype. The former is thought to typically arise by natural selection. The same fundamental phenotypic reward – holding on to prey, catching or escaping – leads to similar outward manifestations of the phenotype, although typically the developmental pathway in the different species is different. There is ‘virtually no’ parallel convergence in genotypes. Convergence in gene sequences generally arises as a result of stochastic variation. If one has two diverging lineages, the limited number of changes available to each DNA base pair (3) results in a significant chance that a base pair held in common by two sequences is not there due to homology (common ancestry) but homoplasy.

It’s important to separate out these two senses. Much cross-talk arises because people are talking of one as if it were the other, sometimes with the lame justification that ‘it’s all molecules’, or the convergence directly constrains a biochemical system. These are misunderstandings; it’s the distinction between phenotype and sequence which is important, not whether the phenotype is ‘molecular’ or not.

Now, the reason for this discussion is that some people are arguing that homoplasy should cause one to reject common descent. So here is their opportunity to defend that view.

[eta – whatever one thinks of Biologos, they provide here an accessible introduction to homoplasy and its relation to homology]

103 thoughts on “Convergence

  1. phoodoo:
    Rumraket,

    Wrong wrong, bad comprehension.What I said was if the same lucky accidents could happen multiple times to give rise to eyes, then the same lucky accidents could happen to give two unrelated individuals the same DNA.

    But phoodoo, they’re not the same. That’s the whole point.

  2. Allan,

    If they’re different, they’re not the same. HTH.

    Phoodoo will have to ponder that for a while. It might be an evilutionist trick.

  3. phoodoo:
    Rumraket,

    They are different lucky accidents?

    They’re different structures phoodoo, there are many different ways to make eyes. They’re convergent in function (the function is sight), but that function is achieved in wildly different ways.

    So?

    So your “If evolutionists are right I can just say in court, that my genes are convergent to get out of a paternity suit”-argument goes into the trash can.

  4. phoodoo,

    What’s to prevent two people having the same lucky accidents but not being related?

    Nothing.

    Nothing but probability. It’s the same thing that prevents all the molecules in a gas from occupying a tiny corner of the box. It’s not impossible, just highly improbable.

    There is quite a good chance for one base pair to end up being the same in two people without them having inherited that base pairing from a common ancestor, because there are only 3 possible changes. Two bases side by side, the chance goes down. 3, it goes down again. It soon gets to being vanishingly improbable – exponentially.

  5. Allan Miller: I see a lot of hand-waving and vague nods in the general direction of something to do with homoplasy from Mung.

    It’s your OP. You seem to think I ought to be disagreeing with it. Why?

  6. Rumraket: The most you can say about convergence is that it’s statistical unlikelihood is directly proportional to the length of sequence at the nucleotide level.

    So it’s Bayesian then?

  7. Allan Miller: Yeah, let’s sweep the entirety of molecular phylogeny under the carpet…

    Can we do that?

    How many different definitions of homology are there? First species, now homology. No wonder Creationists think evolutionary theory is incoherent.

  8. Allan Miller: Two bases side by side, the chance goes down. 3, it goes down again. It soon gets to being vanishingly improbable – exponentially.

    Yea, I agree, sort of like an eye evolving.

    Again. And again. And again…..

  9. phoodoo: What I said was if the same lucky accidents could happen multiple times to give rise to eyes, then the same lucky accidents could happen to give two unrelated individuals the same DNA.

    And for some reason they believe it’s easier (more probable) for eyes than for DNA sequences.

  10. Rumraket: They’re different structures phoodoo, there are many different ways to make eyes.

    LoL! I just visited two nearby eye factories and they both make eyes in the exact same way.

  11. Allan Miller: Nothing but probability. It’s the same thing that prevents all the molecules in a gas from occupying a tiny corner of the box. It’s not impossible, just highly improbable.

    Probability is not a cause. Nor does it prevent anything from happening, as you demonstrate you well know.

    Evolutionary theory is all for lucky accidents, no matter how improbable, until it’s against them.

  12. phoodoo: Yea, I agree, sort of like an eye evolving.

    Again. And again. And again…..

    No phoodoo, not like an eye evolving again and again. There are many pathways to eyes, and the interaction with light in the environment is very beneficial in many circumstances.

  13. : Rumraket: They’re different structures phoodoo, there are many different ways to make eyes.

    But Nilsson and Pelger only made a fake model for one. There are more?!!

    Have you told them?

  14. Mung: And for some reason they believe it’s easier (more probable) for eyes than for DNA sequences.

    Because they’re very different things. You can’t put them up next to each other and pretend that because one is improbable, so too must the other one be. Sorry, flawed premise. Deal with it.

  15. phoodoo: But Nilsson and Pelger only made a fake model for one. There are more?!!

    Have you told them?

    They didn’t make a fake model. And once again your own ignorance about this is becoming an obstacle to conversation.

  16. Mung: Evolutionary theory is all for lucky accidents, no matter how improbable, until it’s against them.

    Incoherent gibberish as usual. You have nothing of worth or consequence to say once again.

  17. Rumraket: They didn’t make a fake model.

    Well, yes technically that’s true, they didn’t actually make the fake model. They just proposed a fake model, that they might make later.

  18. Mung,

    Probability is not a cause. Nor does it prevent anything from happening, as you demonstrate you well know.

    Yeah, I was going to put scare-quotes round ‘prevent’, but I couldn’t be fucking arsed. Clearly, neither of us has any problem grasping this, yet you felt the need to comment anyway.

    Funny how probability ‘prevents’ proteins though, innit?

    Evolutionary theory is all for lucky accidents, no matter how improbable, until it’s against them.

    Mutation-leading-to-difference is clearly not the same as mutation-leading-to-identity, for simple probabilistic reasons.

  19. Mung,

    It’s your OP. You seem to think I ought to be disagreeing with it. Why?

    I’m just hoping for a point, is all. As you often do, you just paste a few lines from a book, say ‘lol’, and then dust your hands as if you’ve said something.

  20. Mung,

    Can we do that?

    How many different definitions of homology are there?

    Several.

    First species, now homology. No wonder Creationists think evolutionary theory is incoherent.

    Yep – very good at feigning confusion, they are. I realise it’s not all feigned …

  21. Allan Miller: Yep – very good at feigning confusion, they are. I realise it’s not all feigned …

    Biology is piecemeal to the creationist. That’s why the fact that evolutionary theory makes sense of biology means nothing to them (it doesn’t make sense of biology for them), and they see no need to bother with it in order to make sense of biology as they have no idea of what making sense of biology even means.

    They happily wallow in ignorance, leaving it all up to a “God” that they don’t understand either. It’s a vicious cycle, they won’t learn the value of evolutionary theory because they don’t value it, and they see no reason to value it because they don’t understand evolutionary theory’s ability to produce coherence in biology.

    Glen Davidson

  22. GlenDavidson,

    There is more to it though – the active process of portraying the field as hopelessly confused and confusing, it’s a shell-game. Sowing confusion over words, as Mung tries to do; exactly the same tactic as trying to make it appear that no two evolutionists agree on anything.

  23. So, what’s phoodoo saying? A process that does not involve selection (stochastic convergence in genotype) is probabilistically the same as one that does (phenotypic convergence on vaguely similar ‘solutions’)?

    Each additional instance of streamlining in an aquatic species renders it exponentially less likely to have arisen?

  24. Mung,

    If you insist on making a straw-man argument, yes.

    Hoyle’s probability calculations are indeed a strawman argument. Doesn’t stop people using them.

  25. Allan Miller: As you often do, you just paste a few lines from a book, say ‘lol’, and then dust your hands as if you’ve said something.

    Good thing no one thinks there isn’t more than one theory of evolutionary change running around out there. Why can’t evolutionists decide? Species, homology, theories of evolutionary change, consciousness. So much to chose from!

  26. GlenDavidson: Biology is piecemeal to the creationist.

    Biology is piecemeal to the biologist. Go ahead and stick your head in the sand and say it isn’t. I would discuss it with you, but you’re not interested in discussion.

  27. Mung: Good thing no one thinks there isn’t more than one theory of evolutionary change running around out there.

    The theory of evolution I’m familiar with predicts every single organism that exists, or ever existed, on Earth can be fitted into an overarching hierarchy of descent and relatedness. Its there another that says something else?

  28. Allan Miller: Sowing confusion over words, as Mung tries to do; exactly the same tactic as trying to make it appear that no two evolutionists agree on anything.

    Lumpers and splitters.

  29. Mung,

    Good thing no one thinks there isn’t more than one theory of evolutionary change running around out there. Why can’t evolutionists decide? Species, homology, theories of evolutionary change, consciousness. So much to chose from!

    There you go again, feigning confusion like a good ‘un. Stupid thing is, you got the thing about homology from me. I pointed out the possible terminological confusion – which actually comes from molecular biologists, not evolutionists. But no, far better to pretend you’re just a poor confused old soul, adrift in a sea of terminological confusion.

  30. Mung,

    Go ahead and stick your head in the sand and say it isn’t. I would discuss it with you, but you’re not interested in discussion.

    lol.

  31. GlenDavidson,

    They happily wallow in ignorance, leaving it all up to a “God” that they don’t understand either. It’s a vicious cycle, they won’t learn the value of evolutionary theory because they don’t value it, and they see no reason to value it because they don’t understand evolutionary theory’s ability to produce coherence in biology.

    I just purchased Futuyma’s 4th addition. It has some cool stuff in it including antibiotic resistance and population genetics. It also contains wild unsupported claims.

  32. Allan Miller,

    Sowing confusion over words, as Mung tries to do; exactly the same tactic as trying to make it appear that no two evolutionists agree on anything.

    Mung clearly has the talent to spin but don’t sell yourself short your pretty good also.

  33. colewd,

    I just purchased Futuyma’s 4th addition. It has some cool stuff in it including antibiotic resistance and population genetics. It also contains wild unsupported claims.

    Go on … (hopefully making it relevant to convergence).

  34. Bill started out OK, but over the past few weeks he’s been slowly turning into Mung. Not a good direction.

  35. John Harshman:
    Bill started out OK, but over the past few weeks he’s been slowly turning into Mung. Not a good direction.

    He didn’t start out all that well, especially if you go by what he was writing at UD. But he does seem to be going more to the trollish side with Mung, indeed. Nothing really new about that, people who already have their cherished pseudoscientific positions actually tend to get worse with increasing education.

    We’ve seen that enough, with Sal going all the way to YECism. If you really don’t want to accept the science, more exposure just gives you more objections to throw at the hated theory. If we’re doing any good here at all it’s certainly not for the Mungs and Coles of this world, it’s for those who don’t post and at least have somewhat open minds as yet.

    Mind you, we may not be doing any good at all, save for a certain edification of ourselves and for entertainment. Which is fine, too, since the true believers are unreachable in any case, so I hardly care about their responses.

    Glen Davidson

  36. GlenDavidson,

    Mind you, we may not be doing any good at all, save for a certain edification of ourselves and for entertainment.

    I think that’s the only sane way to view it. I think worldviews, like accents, are pretty much fixed by the early teens, in the general case.

  37. Mung: There are many ways to make a DNA sequence too Rumraket. It was your argument. LoL.

    But then they wouldn’t be convergent. Please try to keep up.

  38. John Harshman:

    Bill started out OK, but over the past few weeks he’s been slowly turning into Mung. Not a good direction.

    Glen:

    He didn’t start out all that well, especially if you go by what he was writing at UD. But he does seem to be going more to the trollish side with Mung, indeed.

    Failure has that effect on some people.

  39. Allan, to Mung:

    I’m just hoping for a point, is all. As you often do, you just paste a few lines from a book, say ‘lol’, and then dust your hands as if you’ve said something.

    It’s a lot safer than taking a position. Mung is a timid sort.

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