Pagel on Darwin

Mark Pagel, evolutionary theorist extraordinaire, has published an Insight piece in Nature on Natural selection 150 years on. Pagel, well known for myriad projects in natural selecition theory and adaptation, and for developing with Harvey the widely used statistical phylogenetic method (and for being a reader of my thesis) wishes Charles Darwin a happy 200th birthday, and assesses this question:

How has Darwin's theory of Natural Selection fared over the last 150 years, and what needs to be done to bring this theoretical approach to bear as we increasingly examine complex systems, including human society?

Pagel discusses both the controversial nature of and the sheer simplicity of Darwin's Natural Selection, very briefly summarizes the range of applications that has been made of it, then focuses on the core questions "which cut across the hundreds of specific topics of evolutionary investigation." Pagel will not conclude, as was recently suggested by the New York Times, that Darwin needs to die (or Darwinism at least) for us to get on with our work in applying evolutionary theory. Quite the contrary, in fact.

The core areas Pagel addresses are: Descent with Modification, Variation, Speciation and Adaptation. These concepts are interwoven with questions about the nature of tinkering and perfection and Gouldian contingency. Since Pagel's Insight is itself a well adapted summary of a huge set of questions, it would be absurd for me to summarize it for you here. Just get it and read it. But I will make a few comments on selected items.

Pagel, because he just can't stop himself from doing this sort of thing, compiled and analyzed a huge data set. This consisted of papers "that include the term 'natural selection' in their title, abstract or keywords, recorded separately for subject areas as identified by the ISI Web of Knowledge. Data are derived from a search on 'natural selection' in November 2008, yielding 14,232 hits over all years."

From this he produces a graph that shows several interesting things. For instance, there is a huge range of subject areas in which Natural Selection appears non-trivially. Genetics and Heritability and Evolutionary biology unsurprisingly top the list. Psychology, Nutrition, and Pathology are modestly represented. Meteorology sports several hundred papers with the term. The lowest number is found in Chemistry.

Alarming and disturbing, not to mention annoying, is the fact that the lower-ranked subject areas include most of the medical subjects. This underscores my long time assertion that medical research pays an insufficient level of attention to Evolutionary Theory.

Pagel is a wanton adaptationist. In a paper some years ago, he articulated a position on adaptation that I have slightly modified and named after him, which I call Pagel's Wager. Pagel's Wager is this: If you observe a heritable system in nature, bet it is an adaptation. You'll usually win the bet. More importantly, the cost of betting against a heritable system being an adaptation is very high. You miss getting to work on (or at least think about) something interesting.

In the paper under consideration, Pagel summarizes his current thinking on this:

Which view is correct? Not everything is an adaptation: human blood just happens to be red, and human chins might be relics of the way the human jaw develops. But the weight of evidence suggests that it is probably wise not to bet against natural selection. The struggle for existence means that traits have to pay their way. The traits observed now probably improve an animal's chances of surviving and propagating, and those traits that do not will tend to be lost. For example, fish that have adapted to life in dark underwater caves lose the ability to see.

I have also defined another biological guideline called Pagel's Rule. He does not address this concept in the Nature Insight piece, but I'm inclined to give it to you anyway:

"In considering two or more adaptationist explanations for a given trait, where all else is equal, determine which is the most insidious or evil. That is likely to be the correct explanation."

Regarding contingency, Pagel makes an interesting comment (referring to a paper in the same issue of Nature). As you will already be aware, the "contingency" concept, championed by Stephen Jay Gould, is that if you play the 'tape of evolution' again and again, you will get quite different results each time. Pagel mentions what might be Gould's favorite example of this phenomenon: If the whopping big object that hit the earth about 65 million years ago missed, the evolution of mammals would have been a very different story, and it is likely that not even Stephen Jay Gould himself would have evolved. (Well, SJG did not put it exactly that way ....). Pagel reviews some of the evidence testing this idea and concludes that "Contingency does not seem to be the pervasive force that Gould suspected." And he's got a point.

Pagel crams a LOT more into this small paper, including commentary on human evolution and human language, co-evolution, and speciation. I'll leave you with this bit on Darwin and diversification:

The size and details of monophyletic groups illustrate an important feature of life. Rather than designing each species from scratch, as an engineer might, evolution is conservative, using the same designs over and over. Darwin recognized, as the comparative anatomist Geoffroy Saint-Hilaire had before, that the hands of moles, horses, porpoises and bats all used the same bones.

Please find the paper, read it, and enjoy it. Link and references below.

Since I'm sitting at a computer that automatically puts me through to Nature, I am not absolutely certain, but I think you can access the article here.

Mark Pagel (2009). Natural selection 150 years on Nature, 457 (7231), 808-811 DOI: 10.1038/nature07889