Evolution Driven by Humans' Unnatural Selections

In the film "After Earth," the main characters return to Earth after the planet has evolved natural defenses against humans.

In real life, plants and animals are evolving in response to human action as well, although with less malicious intent than on the silver screen.

Tuskless Elephants

Criminal armies equipped with high powered weapons have declared war on Earth's largest land animal. Outlaw organizations, such as Joseph Kony's Lord's Resistance Army, sell black market ivory to finance their rampages in Central Africa.

Elephants can't fight back like the creatures in "After Earth," but evolution is helping to make some of them less attractive to poachers. The frequency of female elephants (Loxodonta africana) without tusks increased from 10.5 percent to 38.2 percent in South Luangwa National Park, Zambia, according to research published in the African Journal of Ecology. The tuskless trait appeared to run in families and may have been a result of tuskless females being spared by poachers. Tuskless mothers survived in greater numbers and hence had more tuskless daughters.

Car-Dodging Birds

U.S. Department of Agriculture scientists estimated that 80 million birds die in collisions with motor vehicles in the United States every year. One bird may be evolving to dodge vehicles.

Over the last 30 years, a decreasing number of cliff swallows have been killed along roads in southwestern Nebraska, according to research published in Current Biology. At the same time, ornithologists' measurements of the birds wings have been decreasing. Birds with shorter wings are more nimble.

The study's authors suggested that automobiles may be killing higher numbers of long-winged birds, leaving more of the nimble, nubbier-winged swallows to pass on their genes.

 Not-So-Bighorned Sheep

Like the ivory poachers, bighorn sheep trophy hunters gun for animals that have the most impressive headgear.

Males in some populations of bighorn sheep (Ovis canadensis) no longer grow large horns, which the authors of a 1995 study in Conservation Biology suggested may have resulted from human hunters' unnatural selection. Having no horns could cause problems for males since they butt heads when sparring for dominance and access to females.

Read more at Discovery News