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More Adaptive Complexity articles
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Richard Lewontin has a piece well worth reading in the New York Review of Books:
There are, however, occasions on which there are orgies of idolatrous celebrations of the lives of famous men, when the Suetonian ideal of history as biography overwhelms us. For Darwinians, 2009 is such a year.
He wanders around a bit, looking at the history of evolutionary ideas and why 19th century industrial capitalism might have contributed to the Origin success as a runaway best-seller.
Lewontin makes a point (about Jerry Coyne's Why Evolution Is True) that's been made before, but that's well worth keeping in mind:
Where he is less successful, as all other commentators have been, is in his insistence that the evidence for natural selection as the driving force of evolution is of the same inferential strength as the evidence that evolution has occurred. So, for example, he gives the game away by writing that when we examine a sequence of changes in the fossil record, we candetermine whether the sequences of changes at least conform to a step-by-step adaptive process. And in every case, we can find at least a feasible Darwinian explanation.
But to say that some example is not falsification of a theory because we can always "find" (invent) a feasible explanation says more about the flexibility of the theory and the ingenuity of its supporters than it says about physical nature. Indeed in his later discussion of theories of behavioral evolution he becomes appropriately skeptical when he writes that imaginative reconstructions of how things might have evolved are not science; they are stories.
While this is a perfectly good argument against those who claim that there are things that are so complex that evolutionary biology cannot explain them, it allows evolutionary "theory" to fall back into the category of being reasonable but not an incontrovertible material fact.
In other words, there is a distinction between a response to creationist 'evolution can't possibly do this' arguments (like irreducible complexity), and the task of showing what evolutionary scenarios have happened in nature. Science isn't about making up stories about what might happen - it's about doing the hard work to find out what really is true.
"There's nothing impossible about long series of small changes. But they are not the only mode of adaptation, or even the most likely one. Populations with additive genetic variation that correlates with fitness will change rapidly under selection. The structure of the additive variation may lead to strong selection on one gene of large effect, or selection in parallel across many genes of varying effects. Series of small changes may be required for some adaptations, but a rapid environmental change (as Lewontin observes for humans) may cause bursts of rapid changes in allele frequencies.
To maintain the slowness of human evolution, Lewontin must do three things:
1. Assume humans are genetically uniform.
2. Where humans obviously are not uniform, argue that variations are uncorrelated with fitness.
3. Ignore any historical or genetic evidence that might contradict 1 and 2.
Keeping in mind the short length of this section of the essay, Lewontin does manage all three of these conditions.
I think it's downright sneaky the way Lewontin reinforces the assumption of human genetic uniformity. He refers to "the human genotype" as if there were only one! By emphasizing that "parts of the human genome are out of correspondence with modern life", he precludes the possibility that some human genomes may be more in correspondence than others. Sure, if humans share a single genome, they can't possibly differ in any adaptive way.
But diversity is the reality. Examples of recent human evolution are fixtures in biology textbooks, from sickle-cell to lactase persistence. These are traits that have rapidly changed in frequency during the last 2500 years, due to changes in recent human environments -- disease for the former, diet for the latter. These rapid transformations in precisely those that Lewontin says are impossible -- environmental changes being "too rapid for genetic adaptation." A number of morphological changes are also evident when comparing archaeological and recent skeletal samples in many parts of the world. Somehow the relevance of these recent changes goes unmentioned in the essay.
http://johnhawks.net/weblog/topics/evolution/selection/acceleration/lewo...