Wednesday, January 07, 2009

Evolution is making some animals weaker

Theodore Roosevelt and another hunter hold the heads of kudus they killed on an African safari in the 1910s

It’s Survival of the Weak and Scrawny
By Lily Huang
Jan 3, 2009

Researchers see 'evolution in reverse' as hunters kill off prized animals with the biggest antlers and pelts.

... The phenomenon has been most apparent in harvested fish: since fishing nets began capturing only fish of sufficient size in the 1980s, the Atlantic cod and salmon, several flounders and the northern pike have all propagated in miniature.

If being smaller is safer, this might be a successful adaptation for a hunted species. After all, " 'fitness' is relative and transitory," says Columbia University biologist Don Melnick, meaning that Darwinian natural selection has nothing to do with what's good or bad, or the way things should be.

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. But there's a cost to not having tusks. Tusked elephants, like the old dominant males on Ram Mountain, were "genetically 'better' individuals," says Festa-Bianchet. "When you take them systematically out of the population for several years, you end up leaving essentially a bunch of losers doing the breeding."

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