Jaden Smith as Kitai Raige in a scene from "After Earth."Columbia Pictures

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.

African elephants on the safari.Corbis

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.

Cliff swallows have adapted to avoid cars.Justin Smith / Wikimedia Commons

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, the birds' wing lengths have been decreasing, ornithologists' measurements have found. Birds with shorter wings are more nimble and better able to dodge cars.

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.

Males in some populations of bighorn sheep (Ovis canadensis) no longer grow large horns. Jon Sullivan

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.

Weeds are even developing resistance to the the kill-all herbicide glyphosate, known by its Monsanto brand name Round-Up.Corbis

A few weeds developed immunity to the herbicides atrazine and simazine within 10 years of the chemicals' first commercial use in the 1950s. Now, hundreds of weed strains are resistant.

Weeds are even developing resistance to the the kill-all herbicide glyphosate, known by its Monsanto brand name Round-Up. American farmers used to be able to plant crops with genetically engineered immunity to the herbicide, then wipe out all weeds with glyphosate.

However, as weeds are evolving their own defenses to the chemical, farmers must develop new strategies, such as spraying increasingly toxic herbicides or labor-intensive hand pulling of weeds. This increases costs to farmers and could subsequently raise food prices.

Abandoned warehouses on the Hudson River in 1973. Inset: Restoration efforts on the Hudson, EPANational Archives and Records Administration/EPA

For 30 years, two General Electric factories dumped approximately 1.3 million pounds of polychlorinated biphenyls (PCBs) into New York's Hudson River. The PCBs wiped out some fish populations and contaminated the survivors. The Environmental Protection Agency banned PCB production in 1977, but 200 miles of the Hudson still hold toxic PCB residues.

However, one fish, the Atlantic tomcod, evolved to thrive in the hostile Hudson. Research published in Science in 2011 identified a genetic adaptation associated with tomcod's resistance to PCBs.

Red-peppered moths have adapted to blend in better.Gilles San Martin, Wikimedia Commons; inset: L. B. Tettenborn, Wikimedia Commons

Originally, most peppered moths sported black spots on their gray bodies, hence the peppered moniker.

This coloration camouflaged them against the light-colored trees and lichens upon which they would alight in European forests. Only a few of the peppered moths went goth with all-black coloration.

Then the Industrial Revolution stained trees black with soot and killed off the lichen. The gray and black peppered moths became conspicuous on the dirty trees and birds gobbled them up. Soon the darker peppered moths took over.

Now, the decline in manufacturing in Europe combined with environmental protection have allowed lighter-colored moths to return.

An eastern coyote.Corbis

Eastern coyotes have posed a puzzle to taxonomists. Are they true coyotes or eastern wolves? In fact, a 2010 study found that they contain mitochondrial DNA from both. The study's authors suggested that the animals be called coywolves to reflect their hybrid heritage.

Ironically, these hybrids may be replacing a previous wolf/coyote hybrid species that European colonists nearly eradicated as they pushed west. The red wolf may have started as a hybrid of coyotes and wolves, then diverged as a separate species that roamed most of the southeastern United States. By the 1970s, the red wolf was essentially extinct in its former range. Now, captive breeding programs keep the species alive.

Although the red wolf is gone, the expanding population of coywolves may mean that a hybrid canid re-evolved to once again roam eastern North America.

A toad is visible in a red-bellied black snake's belly.CONFIRM CREDIT BEFORE USING THIS IMAGE

Having a big mouth got Australian snakes in a lot of trouble. Snakes with bigger mouths could eat larger invasive cane toads. The toads carry a deadly load of poison in their skin that kills most snakes that eat them.

However, a University of Sydney biologist discovered that two snakes, the red-bellied black snake (Pseudechis porphyriacus) and the green tree snake (Dendrelaphis punctulatus) had evolved to be less likely to taste a toxic toad. In areas where cane toads had invaded, both snakes evolved relatively smaller heads and larger bodies compared to their kin in toad-free zones.

Father and son dragnet fishermen hold a giant 45-pound Atlantic codfish aboard their trawler in the North Atlantic Ocean at Gloucester, Mass.Corbis

"Cod is dead," philosopher Friedrich Nietzsche might have said, if he were a fisherman. At least the big ones may be.

Unlike most predators that go for the small and the sick, human fishermen try to catch the largest fish in their reproductive prime. Hence selective pressures have driven some fish species to reach sexual maturity earlier and at smaller sizes. This unnatural selection has led to what journalist Natasha Loder called a "Darwinian debt."

This debt is an evolutionarily stable change in species' biologies. Many fish may continue in their altered life histories even if intensive fishing were ended, according to a study published in the Proceeding of the Royal Society B.