Humans have been driving evolution for millennia, often intentionally: Over the past 11,000 years, we’ve domesticated more than 700 plants and animals, turning the gray wolf into the toy poodle and the bland, bitter watermelon into a sweet, summertime snack. Among the 95 species that make up the world’s most important crops, at least six are human creations.
But we also shape other species indirectly. Hunting, fishing, and harvesting, for instance, can lead to selection against the very traits that we prize. Consider a naturally occurring genetic variant that gives some red foxes iridescent, silver coats. Furs from these foxes fetched higher prices than the traditional rust-colored pelts, leading economically rational hunters to target the silver canids, removing them from the gene pool at disproportionate rates. In 1830 in Eastern Canada, silver foxes made up 16 percent of the population; a century later, that figure had declined to just 5 percent. Likewise, hunters’ hunger for trophy specimens has led to a decrease in horn size among Canadian bighorn sheep.
We continuously reshuffle the planet’s species