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Yesterday's New York Times brought an interesting sidelight, courtesy of the Nebraska deer mouse, on the claims of literary Darwinists. These literary critics co-opt evolutionary psychology to claim that stories and other kinds of literature make us more evolutionarily fit. (More so than newspaper stories or political speeches?) Therefore our human propensity for stories and other forms of literature must come from our genome. The result is that all human cultures, so far as we know, have some form of literature. (But the universality of literature is also the evidence for the claim. Oh well.)
Fitness--that's the core of the claim. Literature makes us fitter. Stories and poems teach me lessons for life that make me more likely to survive and reproduce. Or they let me try out hypotheses for surviving and reproducing. But, as Professor Hopi Hoekstra of Harvard notes, "Fitness is the most important concept in biology. But no one ever measures it." He is leading a team of researchers into the sand dunes of Nebraska to do just that.
Sticklebacks armored and not
Nebraska is part sandy dunes, part dark soil. Scurrying about in both these environments is the deer mouse, Peromyscus maniculatus, doing its mousey business. Some of these mice have dark coats, some have light coats. Professor Hoekstra's team has set up eight different enclosures, half with sandy soil and half with dark. Into each enclosure they put mice of both kinds. Now, running on sand, mice with beige coats should be more likely to elude hawks and owls. They should be "fitter." Dark-colored mice should be easier prey. Conversely, against the dark soil, mice with dark brown coats should be more likely to survive while beige mice would be less fit. With each generation, in the sandy areas, the population of beige mice should grow and the population of dark mice should shrink. Vice versa in the dark areas.
Neat. "People love to tell stories about how species adapt and evolve," said Dr. Rowan Barrett, another member of the team, "but no one ever sees it happen." These scientists hope to discover the mutations responsible for the evolutionary change.
Dr. Barrett's own doctoral research provided a classic case of the story too simple. Barrett worked with the three-spine stickleback, a fish that is armored in the ocean, but lacks armor in lakes. Why? There was an obvious story to explain the evolutionary change. The armor that enabled the fish to escape fishy predators in the ocean made them vulnerable to insect predators in the lakes.
But the story turned out to be more complicated. The armor gene linked to a gene for rapid growth. The lake fish with that gene could breed earlier, get bigger, and survive cold winters better. The crucial factor in the evolutionary change was growth rate, not armor.
The moral of my story (as opposed to the literary Darwinists' story) is, beware the easy story explanation. A true evolutionary explanation needs to establish clear links between genotype, phenotype, and environment. Without factual evidence of a change in fitness and a mutation responsible for it, the claims of the literary Darwinists remain just stories, or Just-So Stories.
Items I've referred to:
Barrett, R.D.H., A. Paccard, T. Healy, S. Bergek, P. Schulte, D. Schluter, S.M. Rogers. 2010. Rapid evolution of cold tolerance in stickleback. Proceedings of the Royal Society B doi10.1098/rspb.2010.0923.
Rosner, H. (2011, August 9). A colorful way to watch evolution in Nebraska's sand dunes. The New York Times, p. D4.
