I’m going to try to post fairly frequent updates about new observations and experiments in evolutionary biology that are relevant to my book. Here’s the first.
Two weeks ago, in an article in The New York Times, Cornelia Dean summarized a recent article in The Proceedings of the National Academy of Sciences about how inadvertant selection by humans has led to evolutionary change. (The original article, by C. T. Darimont et al., can be found here.) Darimont et al. showed that in 29 species for which long-term data exist—species ranging from fish to caribou—human harvesting has led to extraordinarily large genetic changes in size at reproductive maturity and age at which reproduction begins. Actually, these changes were predictable from evolutionary theory, which tells us that if we selectively remove from nature the biggest fish or the largest sheep, we leave behind those individuals who reproduce at a smaller size, and those will be the the ones who contribute their genes to the next generation. This will eventually cause the observed evolutionary changes in age of maturity and body size at maturity.
What is remarkable is the speed of this evolutionary change: it is far faster than normal rates of evolution produced by “natural” (i.e., non-human-based) natural selecction (for example, the changes in beak size in Galapagos finches during periods of drought), and faster even than observed rates of evolution produced by other cases of human-caused selection. These cases supplement and extend the examples of human-caused evolution described in my book, but also add a new dimension because in these new cases selection was inadvertent–people were not trying to change the population, they were just catching the biggest fish and shooting the most desirable rams. It thus differs from deliberate artificial selection such as that involved in dog breeding. It proves yet again that if there is genetic variation for a trait and selection operates on that trait, evolution will follow.