Rapid evolution, even if you don't believe it

I'm often asked how come we can't show evolution happening right now, we always have to rely on historical records for which, you know, “nobody was there to see it.” Well, a recent study by Aaren Freeman and James Byers at the University of New Hampshire, published in Science (11 August 2006) demonstrates how quickly evolution can occur.

Freeman and Byers studied the invasion of the Asian shore crab along the northeast coast, and the response by one of its prey species, the blue mussel. Observations in the field had shown that blue mussels growing in the presence of the predator develop thicker shells, which protect them from the crab's attack. If the crab is not around, the mussel doesn't increase the thickness of its shell, presumably because it would be wasting energy that could be channeled into other directions, like reproduction (this sort of condition-dependent response is called phenotypic plasticity, and I have devoted most of my scientific career to studying it).

Since the shore crab is new to the northeast, how quickly did the blue mussel evolve its ability to respond to the invader? Less than ten years. The crab had been initially documented in New Jersey around 1988, and has since spread to most, but not all, the coastline between North Carolina and Maine. Freeman and Byers therefore sampled mussels from areas where the crab had already arrived and from locations were the invader had still not made an appearance. Sure enough, only the mussels taken from the invaded coastline were capable of the adaptively plastic response, which therefore has to have evolved in less than a decade.

Ah, yes, I can already hear the classic creationist remark: “but it's still a mussel, isn't it? I mean it hasn't turned into another species, like, say, a whale, or a banana.” That sort of statement shows such a profound ignorance of both science in general and evolutionary theory in particular that it would be laughable – if it didn't come from adult individuals with the aim and possibly the power of plunging our country's public education back into the Middle Ages.

You see, most evolution is just like the example of the blue mussel and the shore crab: day to day struggle for survival, where small but significant changes make all the difference for the protagonists involved. Just like mountains form by small incremental movements of the earth's surface, so major differences between species emerge over long periods of time. Too long, apparently, to be contemplated by small minds whose horizon is limited to the 6,000 years or so allowed by the Bible.