A growing number of scientists think human colonization of the solar system is inevitable.
It's not clear when we'll see humans walking around on the moon or Mars, but it's coming, and it's going to have consequences for the human race.
Chris Impey, an astronomy professor at the University of Arizona, pointed out the potential of a particularly radical consequence during an interview with "Fresh Air" host Terry Gross.
Humans that leave the familiarity of Earth could morph into a separate species.
"These people will become an offshoot of the human tree," Impey said in the interview. "They will probably evolve into something else."
And if we have a fully functioning colony where people don't spend all their time on basic survival tasks, change could happen fast.
"They'll evolve physiologically quite quickly, because if the gravity is less — as it would be on Mars or the moon — then they will change," Impey said. "Their physical bodies will change even while they're alive. And then if they have children and grandchildren — then they'll change even more."
We saw something similar when humans first started to explore the Earth. As we moved around the planet, people diversified. The same thing will happen when we start moving around the solar system, but the effects will be even more extreme.
A psychological split will happen too, Impey said. People living billions of miles from Earth will start feeling like their own people group.
It won't look like the galaxy in Star Wars, or other sci-fi universes full of human-like alien races. Any changes will likely be subtle at first — maybe more like a subspecies than a new species.
Impey isn't the only one who thinks this is possible. Other experts in anthropology and biology have written papers exploring how humans might change while living somewhere other than Earth.
It's difficult to predict exactly what the changes will look like, but we can be fairly certain they will happen.
"What we can say, though, is that new environments—for example, new radiation environments, whatever the gas composition is that people are breathing, whatever is the gravity field inside this starship — those basic environmental conditions will reshape the human genome," Anthropologist Cameron Smith told Scientific American. "Subtly, subtly, but they will reshape it."
We see similar effects in people who live at really high elevations, Smith said. Their physiology changes to allow them to live more comfortably in the thinner air and lower pressure environment.
Gravity on Mars is about a third of what it is on Earth. That means humans wouldn't need as much strength, so we'll probably see people with smaller builds and less muscle mass.
You can listen to the full interview:
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