We continuously reshuffle the planet’s species, moving organisms to foreign countries and continents, where they might interbreed with the native flora and fauna or develop traits that better suit their new homes; given enough time and separation from their parent populations, they may eventually become different species.
Even when plants and animals stay put, we radically transform their habitats. We carve up landscapes, leaving isolated, fragmented populations to evolve away from each other in the islands of wilderness that remain. Thanks to deforestation in Central America, the giant helicopter damselfly appears to be splintering into multiple species . And we create entirely novel ecosystems, such as subway tunnels and light-drenched cities. Artificial lights can be hazardous to nocturnal insects, drawing them to their deaths. And so some urban moths are evolving, becoming less attracted to light than their more rural counterparts, according to research released earlier this year. Climate change, and our widespread deployment of pesticides and antibiotics, are also driving the development of new traits in plants, animals, and microbes.
Technology is now giving us new opportunities to alter evolutionary trajectories. Genetic engineering allows us to meddle in genomes directly, and even space exploration could ultimately play a role in speciation, Bull says. “It sounds ludicrous to bring space travel into a paper on speciation and conservation biology,” he acknowledges. But speciation is a long process, one that unfolds over centuries or millennia. “What’s going to happen in terms of space travel over the next two, three, four, five hundred years, given what's happened in the last forty?” If humans transport microorganisms to another planet—even accidentally—those microbes could ultimately evolve into a species unlike anything we’ve ever seen on Earth.
Of course, “species” itself is a fuzzy concept, and there’s no bright dividing line that marks when one damselfly species officially becomes two. The appearance of a novel trait does not necessarily lead to the emergence of an entirely new species—and even when it does, it can be difficult to pinpoint the cause. (Indeed, some scientists believe that the London Underground mosquitoes are migrants from southern climes, rather than descendants of street-level insects that evolved inside the tunnels.)
Still, there's reason to believe that our impact on speciation is significant. In a 2015 paper, biologist Chris Thomas reported that over the last 300 years, more new plant species, primarily hybrid flowers, have materialized in Britain alone than are known to have gone extinct in all of Europe. Overall, the current rate of plant speciation could be hundreds or thousands times higher the natural background rate, he estimated. Meanwhile, human hunting and harvesting may be accelerating the rate of evolutionary change by as much as 300 percent, according to a 2009 study. “Even if a tiny fraction of those species where evolution rates are being sped up resulted in new species emerging, that would still be a lot of new species,” Bull says.