Unnatural selection indeed

Twenty years ago, I remember my grandpa complaining that the white-tail bucks he shot each fall were smaller than the monster deer he'd taken as a young man. The trophy heads in the basement of his South Dakota farmhouse all looked about the same to me, and I chalked up his grousing to nostalgia and the magnifying qualities of time.

Now it looks like he was right. A new study from the National Academy of Sciences supports the long-held notion that by hunting animals, fish and plants, we change them -- and not necessarily for the better. Researchers in the U.S. and Canada found that 29 "harvested" species ranging from bighorn to ginseng evolved three times as quickly, on average, as species that aren't hunted by humans. Over 30 years, the harvested creatures became 20 percent smaller and began reproducing 25 percent sooner. The scientists also found that earlier reproduction wasn't as successful -- fish, for example, produced far fewer eggs than they would have if they spawned a year or two later.

The pressure of hunting is the opposite of what occurs in the wild and even in agriculture. While predators look for easy pickings (the old, the sick, the weak), human hunters and fishers want the biggest, most robust specimens. The small and weak are left to reproduce, and that "change(s) the very essence of what (these species) are and what they can do reproductively," says ecologist Chris Darimont of the University of California, Santa Cruz, lead author of the study (quoted in Wired Science).

Darimont said what he called "evolutionarily enlightened" fishing and hunting management was slowly taking hold, as the realization has sunk in that the sheer number of fish in the pond isn't the only important metric for the system.

"Harvest managers often don’t recognize differences among individuals. That's where evolutionary biologists start," Darimont said. "There's an incredible amount of diversity among individuals, and this matters because they might differ in how many babies they have and what they look like, and that sets in motion a whole bunch of things." 

There might be an upside to hunting pressure on certain animals, though. Ed Abbey advocated hunting cows, which he called "slow elk": "I realize that beef cattle will not make sporting prey at first. Like all domesticated animals (including most humans), beef cattle are slow, stupid, and awkward. But the breed will improve if hunted regularly. And as the number of cattle is reduced, other and far more useful, beautiful, and interesting animals will return to the range lands and will increase."

UPDATE (added 1/14/09): Speaking of trophy hunting, check out this rather disturbing story about the lengths that  one hunter went to to obtain a record-book elk trophy.