Saturday, January 03, 2009

Evolution in Reverse

There's a very interesting article in the latest Newsweek called "How Hunting is Driving Evolution in Reverse," subtitled "It's Survival of the Weak and Scrawny." The basic premise is that by selecting the biggest, fittest, most extraordinary animals as trophies, humans are altering the gene pool with the effect that hunted species are getting smaller:
"Researchers describe what's happening as none other than the selection process that Darwin made famous: the fittest of a species survive to reproduce and pass along their traits to succeeding generations, while the traits of the unfit gradually disappear. Selective hunting—picking out individuals with the best horns or antlers, or the largest piece of hide—works in reverse: the evolutionary loser is not the small and defenseless, but the biggest and best-equipped to win mates or fend off attackers."
The example of the increase in "tuskless" elephants is quite interesting:
"Tusks used to make elephants fitter, as a weapon or a tool in foraging—until ivory became a precious commodity and having tusks got you killed. Then tuskless elephants, products of a genetic fluke, became the more consistent breeders and grew from around 2 percent among African elephants to more than 38 percent in one Zambian population, and 98 percent in a South African one. In Asia, where female elephants don't have tusks to begin with, the proportion of tuskless elephants has more than doubled, to more than 90 percent in Sri Lanka."
Other examples are cited in the article, including a study on Canadian bighorns turning into "little bighorns" that seemed credible.

The evidence isn't overwhelming, but the premise makes sense, and doesn't seem to be anything new. PSU archaeologist Ken Ames has shown that selective hunting of male antelope to preserve herd size has been going on in the Middle East for 10,000 years or more. Similarly, the steady shrinking in size of North American bison over thousands of years has been explained in terms of smaller specimens having shorter gestation periods that make them less susceptible to human hunting than bigger animals that stay pregnant longer.

But perhaps selectively going after "trophy" animals represents a new type of natural selection that we should rethink? I completely understand the impulse of wanting to find that special trophy animal, but if we want to maintain the health of species through hunting, people may want to occasionally take on the traditional role of wolves--eat the small, scrawny, and weak--and find a way to make sure da 30-point buck (or at least some of them) keep breeding.

No comments: