Humans Are Evolving? Not So Fast.
The average human is about 4 inches (10 centimeters) taller now than 150 years ago. That huge change seems to show off evolution in action. But it really doesn't. Genetically, we aren't very different from how we were a century ago, or even a millennium ago.
As much as you might point out that supermodels are tall, or that tall people get the most matches, the tall have not been propagating their genes more than their short counterparts—certainly not over just the past couple generations, which is too brief a time for evolution to change us this way. We're taller nowadays thanks to better nutrition. Genes determine your maximum possible height, but if a baby born today to average parents spends their life eating as poorly as people did in the 1800s, they will grow up the same height as people from the 1800s.
People are different now from people a few centuries ago because of their environment, not evolution. Consider another big change: puberty. Puberty hits girls earlier than ever now (boys too, but the change has been more with girls). The average age for the onset of puberty worldwide has dropped by three months every decade for the past 50 years. If puberty advanced a tad over the course of dozens of generations, we might look to evolution to explain why, but this quick change has to be something else. Maybe it's obesity, maybe it's chemicals, maybe it's something that doesn’t sound scary, but it's not genes.
We talked here recently about another shift: Average body temperatures have been dropping over time. You might be tempted to invent some evolutionary explanation, about how humans are adapting genetically to controlled climates by cooling down. But no, there's no way for evolution to kick in that quick. Biological thermoregulation is the same as a few decades ago, but because we're healthier overall, fewer feverish people slip into the samples and mess with the measurements.
In fact, it's possible humans won't be experiencing all that much natural selection going forward. Demographics will keep changing, which means some genes will become more common or less common, but unlike every other species, humans no longer exist on a continuous spectrum where genes determine how likely you are to live long enough to breed. Instead, a bunch of factors other than your genes affect whether you'll have kids—including (hopefully foremost) something that isn't a factor for animals at all: whether you want to have kids.
That's a good thing. Sure, our feet will never evolve into sneakers, not even in ten thousand years, because incrementally thicker foot soles increase our chance of breeding by 0%. But we don't need to evolve sneakers. We can just wear sneakers. And ever since we invented language and society, we have better ways than genes of passing on such advantages. You might say we've evolved past the need for evolution.
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Top image: Carolyn WIlczynski