“Is Evolution Predictable?” asks a piece in Science. Here’s the first paragraph:
If one could rewind the history of life, would the same species appear with the same sets of traits? Many biologists have argued that evolution depends on too many chance events to be repeatable. But a new study investigating evolution in three groups of microscopic worms, including the strain that survived the 2003 Columbia space shuttle crash, indicates otherwise. When raised in a lab under crowded conditions, all three underwent the same shift in their development by losing basically the same gene. The work suggests that, to some degree, evolution is predictable.
The “some degree” part is the catch. I’m a big fan of general ideas, but the more I learn about evolution the more suspicious I become of broad truths. A given dynamic often has some degree of validity, but extending it too far leads to error or confusion in innumerable specific cases. Evolution may be the most robust and powerful theory for deductive inference in biology, but even here rationalism has its limits. For example, before the rise of molecular methods in exploring polymorphism the debates as to the nature of genetic variation in natural populations tended to focus on outcomes based on adaptive pressures. One school followed R. A. Fisher and argued that polymorphism was strongly constrained by negative selection, with periodic bouts of genetic diversity at a given locus as a positively selected allele was in transience between ~0% and ~100%. Sewall Wright on the other hand suggested that balancing selection (e.g., frequency dependence, heterozygote advantage, environmental heterogeneity) would maintain polymorphism within a population. The logic in both cases was clear, crisp, and plausible. But it turned out that in a deep way the argument was in the “not even wrong category.” Neutral theory and its heirs pointed out, correctly it seems, that at the molecular level most variation was driven by non-adaptive forces such as random genetic drift. Though some thinkers had conceptualized the model in its broad outlines prior to the empirical results, it was the latter which crystallized the need for a robust model and marginalized the older debate centered around adaptation and natural selection. But even here neutrality is not a model to explain it all. There are cases where adaptation and natural selection are relevant. In some instances you see classical dynamics with transients generated by positive selection sweeping through populations, and in other cases balancing dynamics may be operative. The overall point is that we must always be careful about bald assertions of the form “the latest research overturns….” in this area. Evolution is such a sprawling and cosmopolitan intellectual empire. Nature is subtle and richly textured, and our conceptual frameworks map onto the shape of reality only coarsely.
As for the paper itself, it’s nice and elegant. Patrick Phillips, who knows a thing or two about evolution and elegans is quoted in Science as saying that “”It’s an amazing study….” The letter to Nature is Parallel evolution of domesticated Caenorhabditis species targets pheromone receptor genes. Here’s the abstract:
