Humans are powerful agents of evolutionary change: Wild animals and plants that are hunted or harvested evolve three times as quickly as they would naturally, according to a study from the University of California at Santa Cruz. In our quest to bag the biggest and the best, we introduce selective pressures that favor less desirable creatures, such as those with smaller bodies or less majestic horns. Hunting also gives a competitive advantage to animals that have babies when they are younger, before they become tempting targets for humans.
A team led by biologist Chris Darimont combed through data on dozens of species—predominantly fish but also bighorn sheep, caribou, marine invertebrates, and two plants. (“Hunters also want the biggest ginseng,” Darimont says.) Animals that are routinely subject to pursuit are, on average, 20 percent smaller and reproduce at a 25 percent younger age than what would be expected without human influence, the researchers determined. Predation is not the only way that people affect populations. Creatures that are exposed to environmental influences like pollution also experience accelerated evolution, although the effect is less dramatic.
The resulting changes have ripple effects, Darimont notes. Smaller and earlier breeders often produce fewer offspring, for instance. “Size really matters,” he says. “If a harvested animal keeps shrinking, it may no longer be prey to its predator. The whole food web can be altered.”