Thursday, July 10, 2008
Once again an evolutionary puzzle has been illuminated by an expedition into one of deepest, darkest regions known to humankind: museum drawers.
The Chicago Tribune is reporting, based on an article, "The Evolutionary Origin of Flatfish Asymmetry," appearing in Thursday's edition of the science journal Nature, that the issue of how the eyes of flatfish, such as sole, plaice, turbot, flounder and halibut, wound up on the same side of their head.
Essentially, Matt Friedman, a 28-year-old University of Chicago doctoral candidate, discovered a series of fossil flatfish in museum collections, the significance of which had not been recognized before, that formed a "transitional series" showing one eye socket slowly migrating from near the top of the head towards its modern position, thus favoring a slow evolution of the eye position over some sort of "sudden" appearance of the trait. In a paragraph that will doubtless set Larry Moran's teeth on edge, but which we must remember is the work of a journalist, it is explained:
Scientists have until now largely assumed the asymmetrical, one-sided eye arrangement was a trait that must have arisen suddenly in flatfish because they could not see a benefit for the fish if it took millions of years for an eye to migrate from one side to the other. Even Charles Darwin had trouble answering critics who used flatfish and their strange eyes as an argument against his evolutionary theory after he published it in 1859.
In 1871, St. George Jackson Mivart, a Catholic lawyer and zoologist, published "On Genesis of the Species" as a challenge to Darwin, and prominently used the example of flatfish and their eyes in his argument.
"Darwin feebly responded with a scenario that relied on evolution of inherited traits," said Friedman, and the flatfish argument has been an arrow in the quiver of anti-evolutionists ever since.
It seems to me the important aspect is that these fish grow up to lie on one side. Are there any other species that also have this habit, perhaps to a less-developed extent? I speculate that the habit arose first, and was reinforced by larval development that produced asymmetry.
I've published an addendum. I think you'll enjoy. ;-)