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Michael: Evolution has given us some useful abilities. Over the past millions of years, we’ve evolved to stand on two legs, use tools, and develop language. And as recently as a few thousand years ago, humans were still evolving. Part of what drives evolution is natural selection — where those with traits that make them better adapted to their environment tend to survive long enough to pass on those traits to their offspring.

Modern medicine can sometimes interfere with that process, since it keeps people alive who maybe otherwise wouldn’t be. But that doesn’t mean humans are done evolving. One recent example of human evolution is the fact that 35% of adult humans can digest milk. 7,000 years ago, not nearly as many people could to do that. Instead, mainly babies drank and digested milk, so they could get energy from the lactose in their mother’s breast milk.

But when we domesticated cattle, the mutation that allowed certain people to digest milk as adults became something that helped them survive, since they had an extra source of nutrition. A few thousand years later, being able to digest lactose is pretty normal.

So, humans were still evolving in the not-so-distant past. And a lot of scientists think that we still are — and we might even be able to predict what future humans will be like. For one thing, it’s possible that in the future, women will be shorter and slightly heavier than they are now. Researchers figured this out using the data from the Framingham Heart Study, which tracks the medical histories of more than 14,000 people who live in Framingham, Massachusetts. The team wanted to know what traits gave women higher reproductive success.

They found that shorter, slightly heavier women tended to have more children -- and those traits were passed on to their children. If this trend continues, in ten generations the average woman might be about 2 centimeters shorter and a kilogram heavier. Another possible difference between us and future humans is that their brains might be a bit smaller.

Which is weird, because for most of human history, brain sizes tended to get bigger over time. But over the past 20,000 years, the brain size of homo sapiens has decreased. During that time, the average volume of the male brain has shrunk from about 1,500 cubic centimeters to about 1,350 -- about a tennis-ball-sized difference. A similar decrease in brain size happened for women, too. But why the change?

One possibility is that our brains are smaller thanks to the emergence of more complex societies. As population density increased, and there was more division of labor, humans didn’t have to be as smart to stay alive, so their brains didn’t have to be as big.

Other scientists think our brains have been shrinking because we’ve become more tame. See, domesticated animals have smaller brains than their wild counterparts -- probably because if a wild animal isn’t smart enough, it won’t survive too long. So, like domesticated animals, maybe our brains have gotten smaller because we aren’t constantly worried about things like being attacked by predators.

But a shrinking brain also might not mean that the human species is getting dumber -- instead, our brains might just be getting more efficient. Having a big brain uses up a lot of energy, so if it’s a little smaller and more efficient, we don’t need as much energy to stay alive. That said, a recent study of the skulls of Americans showed that they’ve actually been getting bigger since the mid-1800s. But that’s probably because of better nutrition and not an evolutionary change. So if we factor out the effect of better nutrition, it’s possible that the shrinking trend will continue in the future.

Even if natural selection isn’t what drives the future evolution of our species, we might artificially evolve ourselves through genetic engineering. As we learn more about what all of our genes do and how to modify them, we’ll be able to eliminate certain genetic disorders and maybe even diseases related to getting older. And eventually, we might be able to design people like we design avatars in video games -- altering things like height, intelligence, athleticism or any other trait. So, whether the changes are natural or artificial, humans of the future might be very different.

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