Evolving Thoughts

In addition to the “missing link” trope that is being dished out about the new primate fossil, is another one, more subtle and insidious: it’s the ancestor of all primates. How do they know that? Consider a biologically realistic scenario: at the time there were probably hundreds of species of small bodied mammals with tails and feet like that. One of these species may be the ancestor of all primates, but what are the odds that a specimen from that species is the one that was preserved? Just as all primates now look remarkably similar overall, but one may be the common ancestor of a group in 50 million years or so without being the one that is fossilised, the characters of this species may in fact be shared primitive (in the sense of “came first”) traits of its group. So-called plesiomorphic traits, or underived traits, are no indicator that the specimen is a member of an ancestral species, only that it is a member of a group of species, one of which was the ancestor. We don’t even know what extant species is the ancestor of Darwin’s finches, and we have access to their biogeography, molecular properties, development, behaviour and mating systems. How can we be sure this was “the” concestor (Dawkins’ term for common ancestor) of all primates?

We’ve been bitten by this mistake many times before. Archaeopteryx was supposed to be the ancestor of birds. Neanderthals (now spelled without the “h”) were supposed to be “primitive” (i.e., came first) humans. Both are regarded as side branches of the lineage leading to birds and humans, but they show many traits that would have been shared with other species of their group at the time. And we rarely have reason to think we have a sufficient record of all species, as the Hobbit shows (it is regarded as not even a descendent of the H erectus hominids we know were in Asia around the right time).

History loses information. To make claims about history one needs positive evidence, ruling out, or at the least making extremely unlikely, alternative hsitories. Phylogenetics does not rule out all alternative histories, just some subsets. Phylogeny can rule out that a species is an ancestor, but it cannot rule it in. “Ida” may be our greatn parent, but equally it may just be a long lost cousin.

Comments

  1. #1 Paul Browne
    May 20, 2009

    Good post John. It’s a shame to see so many organizations that should know better, as well as news outlets who can be expected to over sell, jumping on “ancestor of all primates” bandwagon. It’s not just a case that the framing is wrong or that they are taking the wrong angle on the story, but that the story itself is probably incorrect.

    This episode will probably come back to haunt the paleontologists and evolutionary biologists for years to come as creationists use it as an example of “Darwinists” misleading the public.

    This is a shame since it is a beautiful fossil, eminently newsworthy in its own right (though perhaps not with so many headlines), and could be a great example for explaining evolution by natural selection to the general public. Instead of this they’ve gone for a big splash, whuich will no doubt shortly be followed by the story sinking like a stone.

    I just hopoe that the documentary discusses the find and the various claims made about it in an more balanced and less excitable way.

  2. #2 Paul Browne
    May 20, 2009

    Good post John. It’s a shame to see so many organizations that should know better, as well as news outlets who can be expected to over sell, jumping on “ancestor of all primates” bandwagon. It’s not just a case that the framing is wrong or that they are taking the wrong angle on the story, but that the story itself is probably incorrect.

    This episode will probably come back to haunt the paleontologists and evolutionary biologists for years to come as creationists use it as an example of “Darwinists” misleading the public.

    This is a shame since it is a beautiful fossil, eminently newsworthy in its own right (though perhaps not with so many headlines), and could be a great example for explaining evolution by natural selection to the general public. Instead of this they’ve gone for a big splash, whuich will no doubt shortly be followed by the story sinking like a stone.

    I just hopoe that the documentary discusses the find and the various claims made about it in an more balanced and less excitable way.

  3. #3 marcusa
    May 21, 2009

    All that ancestor-of-humans and missing-link talk is from the media, which misrepresents everything complex. The “reporters” frame everything in the most dramatic light possible. The news practically calls every fossil discovery a “missing link”. And don’t think the news organizations don’t know they’re stirring up the creationism debate with their mischaracterizations; they know.

  4. #4 torrentprime
    May 21, 2009

    This episode will probably come back to haunt the paleontologists and evolutionary biologists for years to come as creationists use it as an example of “Darwinists” misleading the public.
    This was precisely why I thought they made the (sensational) claims they did – this latest find further bolstered (as if it needed it, I know, I know) modern evolutionary theory. The Flat Earthers are always talking about how bananas and peanut butter and what not prove Darwin is a tool of Marxism and Satan, etc; I assumed the over-the-top reporting (IANABiologist, but even I thought the claims a little too pat) was to drive the point home that this find simply reaffirms what we know – evolution happens, happened, will keep happening.
    I don’t want to give these guys too big a pass, but I think their hearts were in the right place.

  5. #5 Ajoy
    May 21, 2009

    Actually, the claim in the published paper is that this
    could be the ancestor of all Anthropoids. That is a group
    including apes (hominoids), Old World monkeys
    (cercopithecoids such as macaque, mandrill) and New World
    monkeys (ceboidae). In short of all primates, except the
    lemur/loris/galagos and the tarsiers.

    This is not a new claim. The fossil is an adapiform, and
    whether adapiforms are the ancestors of anthropoids has
    been under debate. Experts such as Richard Klein (see
    “The Human Career” 3rd edition out just this month) do not
    believe, just as you do, the claim can be settled with
    fossils. Because shared features might be due to convergent
    evolution.

    As for the missing link, I think most people consider that
    to be the last common ancestor of hominins and the
    panini (chimps). From around 7ma – no fossils yet.

  6. #6 Monado
    May 21, 2009

    So it would be better to say that the ancestor of all primates was probably similar to this and occurring about the same time.

    No, if it isn’t short, snappy, and definite, a reporter will simplify ’til it is; accuracy comes last.

  7. #7 Greg Laden
    May 21, 2009

    It is my opinion, and I state as much in my own post on this fossil, that the hype was overdone to the extent that the counter-hype is also overdone. Now, here, I can imagine that a gorilla would take this all personally, and a philosopher could be mainly interested in the hype and framing and stuff, but even on paleo blogs the fossil is getting too little attention.

    In other words, we have more blogging about Ida than for the average newly reported cool fossil, by far, but the least said (relatively anyway) about the fossil itself.

    Which is why, when I got to writing my version of this, I wrote mainly about the fossil and related issues of primate evolution.

  8. #8 Karen James
    May 22, 2009

    “Ida” may be our greatn parent, but equally it may just be a long lost cousin.

    Equally? I would have thought it more likely, and that the specific likelihood would relate to the number of coexisting Adapid species (or perhaps populations).

    Actually, the claim in the published paper is that this could be the ancestor of all Anthropoids..

    Doesn’t the paper claim that the fossil is an Adapid and that, if it is, that is evidence that the ancestor of all Anthropoids was an Adapid – any Adapid, maybe Ida, maybe not.

    I think their hearts were in the right place.

    Perhaps, but they’re paid to have their brains in the right place.

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