Jerry Coyne’s “Seeing and Believing” and convergent evolution

In “Seeing and Believing” (2009-02-04), evolutionary biologist Jerry Coyne reviews two books that discuss creationism/”intelligent design” and their history, and attempt to reconcile religion and evolution: Karl W. Giberson's Saving Darwin: How to be a Christian and Believe in Evolution and Kenneth R. Miller's Only A Theory: Evolution and the Battle for America’s Soul. I enjoyed it enormously and commend it to your attention.

One point in particular caught my eye.

Giberson and Miller assert that the evolution of humans, or something very like them, was inevitable. Given the way that evolution works, they claim, it was certain that the animal kingdom would eventually work its way up to a species that was conscious, highly intelligent, and above all, capable of apprehending and worshipping its creator.

[…] To support the inevitability of humans, Giberson and Miller invoke the notion of evolutionary convergence. This idea is simple: species often adapt to similar environments by independently evolving similar features. Ichthyosaurs (ancient marine reptiles), porpoises, and fish all evolved independently in the water, and through natural selection all three acquired fins and a similar streamlined shape. Complex “camera eyes” evolved in both vertebrates and squid. Arctic animals such as polar bears, arctic hares, and snowy owls either are white or turn white in the winter, hiding them from predators or prey. Perhaps the most astonishing example of convergence is the similarity between some species of marsupial mammals in Australia and unrelated placental mammals that live elsewhere. The marsupial flying phalanger looks and acts just like the flying squirrel of the New World. Marsupial moles, with their reduced eyes and big burrowing claws, are dead ringers for our placental moles. Until its extinction in 1936, the remarkable thylacine, or Tasmanian wolf, looked and hunted like a placental wolf.

[…] Miller and Giberson are forced to this view for a simple reason. If we cannot prove that humanoid evolution was inevitable, then the reconciliation of evolution and Christianity collapses. For if we really were the special object of God’s creation, our evolution could not have been left to chance. (It may not be irrelevant that although the Catholic Church accepts most of Darwinism, it makes an official exception for the evolution of Homo sapiens, whose soul is said to have been created by God and inserted at some point into the human lineage.)

[…] We recognize convergences because unrelated species evolve similar traits. In other words, the traits appear in more than one species. But sophisticated, self-aware intelligence is a singleton: it evolved just once, in a human ancestor. (Octopi and dolphins are also smart, but they do not have the stuff to reflect on their origins.) In contrast, eyes have evolved independently forty times, and white color in Arctic animals appeared several times. It is hard to make a convincing case for the evolutionary inevitability of a feature that arose only once.

It would be easy to take too much from this argument against convergence. It is not evidence against convergence of intelligence that it has evolved only once as such, because there hasn’t been time since the first instance for a second to arise — it would be the most extraordinary coincidence if it were to arise twice in distantly-related creatures within the space of a hundred thousand years, so all we know is that we are first. Rather, I think he is arguing that it fails to be evidence for it — that there’s no reason to suppose that every feature of life to be found in the wild, such as the trunk of an elephant, is one that would be “re-discovered” by convergence if a particular branch had failed to flourish. By Coyne’s account, Giberson and Miller seem to be positing exactly that sort of “universal convergence”: Miller writes

But as life re-explored adaptive space, could we be certain that our niche would not be occupied? I would argue that we could be almost certain that it would be—that eventually evolution would produce an intelligent, self-aware, reflective creature endowed with a nervous system large enough to solve the very same questions we have, and capable of discovering the very process that produced it, the process of evolution…. Everything we know about evolution suggests that it could, sooner or later, get to that niche.

I think I see another problem with universal convergence. If evolution naturally filled every possible niche that it was presented with over time, we wouldn’t see the sometimes dramatic successes of species we ourselves carried across the seas. Rabbits are a dramatic success in Australia, for example, where “universal convergence” should lead us to predict that a species more perfectly adapted to the niche they occupy should already have been native to Australia on their arrival.

I’d be very interested to hear from those with greater expertise whether this objection holds up.

Note also this longer blog post on the subject from Coyne and this paper discussing evidence against convergent evolution of intelligence (ht Black Belt Bayesian).