Those who have doubts as to whether evolution can modify the characteristics of a population could learn from an article in the current Newsweek which suggests that humans hunting big game are favoring the survival of the "weak and scrawny."
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. When hunting is severe enough to outstrip other threats to survival, the unsought, middling individuals make out better than the alpha animals, and the species changes. "Survival of the fittest" is still the rule, but the "fit" begin to look unlike what you might expect. And looks aren't the only things changing: behavior adapts too, from how hunted animals act to how they reproduce...
Other species are shrinking, too. Australia's red kangaroo has become noticeably smaller as poachers target the largest animals for leather. 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...
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...
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