Saturday, January 24, 2009

The New Scientist and the "Tree of Life"

Ecographica has an article castigating the New Scientist for its cover stating that "Darwin was Wrong" and the accompanying article by Graham Lawton. Here is the cover.



I have to agree with his assessment. Here is the article in question, which is, if somewhat sensationalized, fairly tame. It focuses on the concept of Horizontal Gene Transfer and the idea that Darwin's original "Tree of Life" idea does not fit modern evolutionary thought:

As more and more genes were sequenced, it became clear that the patterns of relatedness could only be explained if bacteria and archaea were routinely swapping genetic material with other species - often across huge taxonomic distances - in a process called horizontal gene transfer (HGT).

A bit later:

As it became clear that HGT was a major factor, biologists started to realise the implications for the tree concept. As early as 1993, some were proposing that for bacteria and archaea the tree of life was more like a web. In 1999, Doolittle made the provocative claim that "the history of life cannot properly be represented as a tree" (Science, vol 284, p 2124). "The tree of life is not something that exists in nature, it's a way that humans classify nature," he says.

Thus began the final battle over the tree. Many researchers stuck resolutely to their guns, creating ever more sophisticated computer programs to cut through the noise and recover the One True Tree. Others argued just as forcefully that the quest was quixotic and should be abandoned.

Of course, this discussion in no way impugns evolutionary theory. It is roughly analogous to the revelation that evolution does not always proceed slowly beneficial gene by beneficial gene, but sometimes through developmental leaps by way of hox genes. Hence the study of evo-devo.

It has become clear that evolution proceeds much more in the form of a bush rather than a tree and that is how most palaeontologists view things. The problem is that this is the cover of the newsstand copy and people that look at it will think that Darwin was wrong, therefore evolution was wrong. This is a colossal blunder. A statement should be released immediately explaining what the cover means, not that anybody will read it. The creationists will have a field day.

12 comments:

  1. Several things about this. I read about the soup of genes at the base of the "tree" in Carl Zimmer's "Evolution: The Triumph of an Idea" a very low level popular book which was published in 2001, so I don't know why New Scientist is making such a big deal about this seven years later.

    Second, the tree only breaks down at the base. Once we reach sexual reproducing species, or at least in clades higher up like vertebrate or tetropods, or mammals, we do indeed find a tree. Am I wrong about this?

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  2. I was going to tell you about the latest issue of National Geographic, which has the cover article "What Darwin Didn't Know". I thought that was proof enough. But this New Scientist title is a slam-dunk. See, even scientific magazines proclaim DARWIN WAS WRONG!!

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  3. It has become clear that evolution proceeds much more in the form of a bush rather than a tree

    I'm not clear on the conceptual difference there.

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  4. It has to do with the difference between lineal or direct ancestry and collateral ancestry. Your direct ancestors are your mother and father and your two sets of grandparents. Collateral ancestry is your uncles and aunts on both sides. You are not directly descended from them but you share their genes. Creationists are fond of saying that Archaeopteryx is not a transitional form because it does appear that it was the direct ancestor of the first birds (Protoaves and the like). That sidesteps the fact that Archaeopteryx was just one more variation on a theme that was common between 60 and 90 million years ago--the appearance of birds from dinosaurs. It and Protoaves are both transitional. This is the "bushy" aspect of evolution.

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  5. Sorry, I misspoke. Protoaves predates Archaeopteryx by about 25 mya. I meant to say "Protoaves and the like preceded it."

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  6. Jon, the problem is it makes for a sensational cover to say "What Darwin didn't know." The things that Darwin did not know are legion. He didn't know about DNA, microorganisms, population genetics, and a whole host of other things. Those discoveries have come about later. The most ground-shaking discovery in recent years is that of homeobox or hox genes, which appear to regulate development on a grand scale and are found in all forms of life. Darwin wasn't wrong. Natural selection is the grand unifying theme in evolution and without it, there would be no "descent with modification" as he so pithily put it.

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  7. Pete, as I mentioned in the last note, the tree is more like a bush, with lots of related branches. I guess the difference might be related to modern species as opposed to palaeospecies. it is, of course, harder to draw direct relationships between palaeospecies, so we infer relationships where we can. As to why New Scientist is doing this, who knows. The sensational aspects of it are annoying. I still think it is a huge mistake. It will just fan the flames.

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  8. Ah, so the bush/tree distinction is between density, not so much general structure.

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  9. The way that Donald Prothero puts it, it is between an older phenetic view of evolutionary relationship that are time-dependent and more recent cladistic relationships that do not necessarily rely on a time component but are organized around trait polarities. The typical trait polarities are "plesiomorphic" or traits retained from an ancestor and "apomorphic" or traits that are new to a species.

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  10. Wow, I wish I knew more about evolutionary theory.

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  11. Here ya go. This is UC Berkeley's evolution page.
    http://evolution.berkeley.edu/

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