Humanity Is Killing Off Thousands of Species. But It’s Creating Them, Too
During World War II, Londoners often attempted shelter from German bombs in the citys subway passageways. There, they encountered other types of enemy: hordes of voracious mosquitoes. These werent your typical aboveground mosquitoes. They were natives of the metro, born in ponds of standing water that pockmarked the underground passageways. And unlike their open-air cousins, Londons subterranean skeeters seemed to love biting humans.
Fifty years after the war objective, scientists at the University of London decided to investigate the subway population. They collected eggs and larvae from metro passageways and garden ponds and reared both populations in the lab. The passageway glitches, they confirmed, preferred feeding on mammals over birds. And when the scientists put males and females from different populations in close quarters designed to encourage mating , not a single pairing made offspring. That sealed the deal: The underground mosquitoes were a whole new species, adapted to life in the metro tunnels people had built.
Its tales like that one that got Joseph Bull reasoning. As a preservation scientist at the University of Copenhagen, he hears a lot about how humans are driving other species extinct. If the current rate remains steady, countries around the world is on its way to its sixth mass extinction, a severe event on par with the meteorite impact that killed the dinosaurs. But he wondered if there might be a flip side. I hadnt really watched any kind of analysis of whether all these kinds of activities that humans get up to around the planet, whether and how they cause new species to emerge, he tells. The Anthropocenewhile not quite yet an official geological epoch, still a supremely useful conceptis defined by the myriad styles in which humans affect the Earth. Civilization is destructive, but its generative too, sometimes in disturbing styles. A new world will emerge out of the Anthropocene, and it will be shaped by the species humans create and foster as well as the ones they kill off.
The most obvious route that people make new species is through domestication. By picking out the traits in a wild population that are most beneficial to humans and breed for them, people can force-out evolution in different species, Bull tells. Wolves become puppies, nubby grass becomes maize, wild boars become pigs.
But humans can drive speciation in other, less purposeful styles. Its important to be considered the creation of new species as a process, Bull tells. One of the most dramatic styles people put that process in motion is by moving each member of an existing species from one place to another. Sometimes those individuals die in the new environment. Sometimes they hang on and interbreed with native species. And sometimes, they take over, like kudzu in the American South or snakes on Guam. Over time, the new environment exerts different pressures on the invasive population, causing it to diverge from its ancestors. The invasive species might also change the game for native species, pushing them in new genetic directions( if, of course, it doesnt just drive them extinct ).
Although hunting is one good way to drive a species extinct( just ask the passenger pigeon ), it can also spurring evolution by removing certain types of individuals from a species gene poolbirds of an easy-to-see colouring, say, or fish large enough to be caught in a net. No new species is known to have been created through hunting alone, Bull tells, but given enough time its far from impossible.
Finally, we have the process that created the underground mosquito: Peoples propensity to create whole new ecosystems, including and especially cities. Populations of animals colonize these new environments and adapt to their demands, from mosquitoes developing a savor for mammals blood underground to city birds becoming better problem-solvers than their rural relatives.
Keeping these mechanisms in mind, Bull tallied up humans impact on species in a paper published today by the Proceedings of the Royal Society B . During the last 12,000 years, scientists have recorded 1,359 plant and animal extinctions. Meanwhile, humans have relocated 891 plant and animal species, and domesticated 743 for a total of 1,634 species. It seems that human-driven speciation could be as much a mark of the Anthropocene as extinction is.
Of course, extinction, like speciation, is hard to document as its happening. Many species likely disappear before scientists even know they are there. Thats why extinction rates are usually calculated with extrapolations and models, but even they dedicate wildlydifferent numbers. Thats all to say that many more than 1,359 lifeforms are most likely run extinct in the past 12,000 years. Though its possible humans make species without seeing them, too. Just think of the wild world of antibiotic-resistant microbes, which evolve so fast in response to drugs that its dangerously difficult to keep up.
Number of species, however, is just one route measure the effects humans are having on natureand maybe not the best route. Drive keystone predators like wolves or sharks extinct and entire ecosystems breakdown , no matter how many new species pop up to replace them. Whats more, older species can carry millions of years of evolutionary history in their genes; if they go extinct, that diversity is lost. Anthropogenic species represent a nanosecond of the evolutionary time that many natural species have passed through, tells Christopher Dick, an evolutionary biologist at the University of Michigan. In preservation, there is no comparing a 10 -million-year-old tree or turtle species with a decades-old strain of bug or plant.
Bull agrees that speciation and extinction dont cancel each other out. If we only use number of species as a route of measuring progress that someone builds on preservation, then were missing a load of other major consideration, he tells. We cannot replace something lost with something gained when it comes to nature. Human-driven speciation may turn out to be a calling card of the Anthropocene. But no matter how many species of underground mosquitoes humanity inadvertently makes, they wont make up for what it destroys.