People are a great and terrible influence on the world.
You already know about antibiotic and pesticide resistance. You’ve heard that mice and rats evolve immunity to poisons. But there are other, sneakier ways that the rest of our planet’s ecosystem has adapted to humanity’s presence.
The reality is that living things are constantly ‘evolving,’ just not usually at a rate that we can pick up on. Every new birth is an opportunity to introduce a mutation that could wind up being beneficial to the organism carrying it. Maybe that critter is a little faster or stronger or smarter or more colorful than average, and it manages to produces slightly more offspring than its brethren—creating babies with the same advantage. In a world where water, nutrients, and sex are plentiful, this mutation might not matter much.
But the reality is that the world is a harsh place for most creatures that live on it. And humans in particular tend to place a lot of stress on the environment. We shoot the biggest deer so that their smaller cousins thrive, and put toxins into the water to make competition fiercer for the fish that live there. We introduce invasive species that out-eat native organisms to the point of extinction. We mow down grass and plant crops instead. These changes often apply a selective pressure on the creatures living there, and those with beneficial mutations will ultimately win out. It’s just a question of how quickly they can evolve.
One recent study found that the bird known as the great tit may be evolving bigger beaks; the better to eat out of our bird feeders with. Here are a few more examples of plants, animals, and viruses that are evolving to deal with us—right before our eyes.
Puberty is tough for everyone, and lately we’ve been forcing Atlantic cod into it early. Our tendency to capture and eat the fishies as soon as they’re moderately sized means that we’re not allowing many of them to fully mature. Since the ones who can reproduce earlier in life are the ones who actually get the chance to reproduce, maturity is coming earlier as the generations go on. We’re also unintentionally making things more difficult for ourselves, because cod are shrinking. By catching the big ‘uns, we’re selecting for the small fry to persist and thrive, thereby making the average fish scrawnier.
For most of their evolutionary history, bighorn sheep competed to have, well, the biggest bighorns in order to impress potential mates. But because of the human proclivity to want The Biggest Thing, especially if we’re hanging it on a wall, we’re imposing a new pressure on the population. Suddenly, big horns are a liability as well as a sexual advantage. They’ve now shrunk by as much as 25 percent due to our hunting habits.
As a snake, it’s generally best to eat as much toad as possible. Your jaw and stomach will allow it, so why not go for the extra portion? So when people introduced the poisonous cane toad to Australia, the native snakes went all in. But the ones with the largest jaws ate the fattest toads, which often contain enough poison make death the dessert course. So smaller mouths have persisted in the population as a portion control mechanism, preventing them from accidentally killing themselves instead of living to make more babies.
Few people—nay, few things—want to swim in the Hudson River. It’s really best when viewed from a distance, and preferably on a cool day to avoid the stench. But Atlantic tomcod are taking advantage of the low real estate values by adapting to become immune to the many toxins floating about in the water. They can now make their home wherever they please.
Holing up in nests beneath highway overpasses makes cliff swallows liable to becoming roadkill. When ornithologists noticed that the number of dead birds was declining despite a growing population, they investigated and found that the birds had developed shorter wings that made them more agile.
Humans eat more corn today because of corn lobbies, but deer mouse do it because...well, because of corn lobbies. The fact that we grow so much corn (15.1 million bushels a year, to be exact) means there’s an abundance of corn out in their native prairies. The average deer mouse jaw is too small and weak to eat the kernels, so they’re evolving larger ones to dine on the delicious cobs.
Out in nature, seeds that float easily on the wind help plants to sow their wild oats (literally). In cities...not so much. A plant growing in a tiny urban park won’t do itself any good by producing seeds that blow out onto the paved street. Having heavy seeds that drop straight down, where there’s likely to be soil, is preferable to setting your potential progeny afloat on a breeze. So the Crepis sancta plant is doing just that: evolving to produce more of the heavy variety of its seeds.
The whole reason you have to get a flu vaccine every year (or rather, that you should) is because the influenza virus mutates and evolves so rapidly. By the time a strain travels halfway around the globe, it’s already differentiable from its starting point. If the flu were more stable, we could vaccinate against it for life like we do with other diseases. Instead, as soon as we become immune to one particular strain, the viruses has changed and can reinfect us.
Perhaps the most classic example of human-driven evolution is the peppered moth, which, despite its name, does not have a pleasantly spicy taste. Instead, they have a peppered pattern on their fuzzy wings that helps them blend into their surroundings and avoid predators. During the Industrial Revolution, the moths’ coloring became much darker to blend into the soot-covered buildings of highly-polluted England. A geneticist named Michael Majerus finally confirmed the Darwinian shift using nearly 5,000 moths—and dogged determination.
You don’t want to think about the fact that some sea snakes live near humans, but they do (don’t worry, they don’t attack people). And because they swim in polluted waters, they’ve developed darker skin; not because they’re trying to blend in, but because the melanin inside their skin can bind to pollutants. When they shed, the toxic chemicals float away, too.
You can put up whatever signs you want—humans like picking flowers. But humans are also lazy, so we tend to pick the tallest ones that are easiest to reach and the most obvious. Some flowers, like the Tibetan snow lotus, have thus evolved shorter stems so as to be less obtrusive. Unfortunately, people use the lotus for medicinal purposes, so the strategy only works for so long the average height of the blooms is low enough that once-dwarf-like stems are tall enough to be noticeable again.
Human Immunodeficiency Virus has the highest mutation rate of any biological entity. Viruses mutate quickly in general because the machinery they use to replicate is error-prone and often doesn’t correct mistakes, so there are more mutations in the first place. And because they replicate so quickly, a single beneficial mutation can spread through an entire population rapidly. It’s so fast, drug resistance can occur in a single day, which is we have to treat it with a whole cocktail of drugs in round one. That’s why we can’t come up with a vaccine for it: by the time we made one, the shot would already be useless.