How humans are forcing other species to evolve
Presumably everybody knows the basic depressing mechanisms of natural selection: In response to a cruel and unforgiving environment, those creatures that can adapt best or are already best-suited survive to reproduce, and everyone else dies horribly. It's all red-in-tooth-and-claw-y, and humans are well out of it, right? Yeah, well, about that: Turns out that now we've become the cruel and unforgiving environment. Whoops.
An article (behind a reg wall, so we'll give you the highlights) in this month's New Scientist collects the effects humanity has had on shaping our fellow creatures:
- Tuskless elephants: In Zambia, the proportion of tuskless female elephants went from 10 percent to 40 percent in 20 years. In Sri Lanka, fewer than 5 percent of male elephants now have tusks. This is all due to poaching — elephants without tusks live longer and reproduce more, because poachers will kill the whole animal just to get a few cubic inches of ivory.
- Short plants: Flowers that get picked a lot — like the Tibetan snow lotus, which is used in traditional medicine — end up shorter, since more unassuming plants are less likely to get harvested. It's the literal version of Tall Poppy Syndrome.
- Tawnier tawny owls: Animals with more summery coloring do better in an environment affected by global warming. Finnish tawny owls with grey coloration do better in the snow, but when there's less snow, the browner ones thrive, and the species as a whole has become more and more brown over time.
- Early-onset fertility: All kinds of species breed earlier in the year to account for global warming. Red squirrels, for instance, are breeding earlier in the spring as the climate warms. And field mustard plants in California flowered nine days earlier in 2004 than they did in 1997, trying to breed before drought set in. Species that aren't able to shift their schedule, like the pied flycatcher (which is a bird; it's hard to tell from the name) may end up threatened.
- Early-onset fertility, part two: Animals that are frequently killed for food and industry, like fish, may adapt with earlier sexual maturity. If you've got a pretty good chance of being slaughtered as an adult, you'll want to start passing on your genetic material as soon as you can. This adaptation has also been seen in fish populations that have faced deadly disease outbreaks.
- Pollution-resistant fish: Animals that can't adapt to pollution are basically screwed. Luckily, some can. A species called the Atlantic tomcod, which lives in the Hudson river, has become a true city fish; it can swim around in toxic chemicals all day with no ill effect. It works for plants too. Plantains — the leafy weed you used to pull threads out of in elementary school, not the tasty banana analogue — used to have retarded growth due to ozone pollution, but now they just shake it off.
- Pesticide-resistant pests: Like bacteria, critters non grata can develop resistance to the poisons humans use to drive them out. By the time the insecticide DDT was outlawed, 165 or more insect species were immune to its effects. Rats and mice are becoming resistant to the pesticide used to kill them, warfarin, and some are even immune to its replacement, superwarfarin (for warfarin-resistant super-rats!). And anti-lawn partisans will like this one: Weeds are developing resistance to weed-killers.
- Invader adaptations: Human travels and trade tend to pick up hitchhikers — foreign species that, in a new habitat, can end up invasive. Some of the native species' evolutionary responses are really wild. For instance, after the cane toad invaded Australia, snakes evolved smaller mouths. What the hell? Well, snakes with bigger mouths were eating bigger toads that contained more toxin, so they were dying faster, and snakes who couldn't swallow big toads became the dominant variety. And in parts of the U.S. that have been invaded by fire ants, lizards have evolved longer legs, presumably so their bellies don't drag on the ants' mounds and also so they can run the hell away.
- Urban variants: Some species have adapted to living in cities by developing particular traits for urban dwellers. Mosquitoes in the London underground, for instance, are less choosy about their food sources, breed all year long, and can mate in confined spaces. And some city-dwelling weeds have developed heavier seeds that fall closer to the parent, where there is probably dirt, instead of being blown out to unforgiving pavement.
What's this mean for our ability to live alongside nature without totally destroying it? Well, it means nature will make some room for our foibles, which is actually kind of nice, or would be if the foibles it was making room for weren't along the lines of "killing the sh*t out of nature at any opportunity." It also means that "nature" is kind of a moving target — when we figure out how to coexist with the biome around us, we may find it's a slightly different one than the one we started with. And it makes it clear that our more harmful habits are leaving lasting scars even on the species that don't end up on the endangered list.
Unnatural selection: How humans are driving evolution, New Scientist.
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