Going to Mars will change us — and not just in a touchy-feely, metaphysical way.

Over time, we should expect a fair bit of evolutionary divergence between Mars settlers and the human population on Earth, according to Rice University biologist Scott Solomon, who examined this possibility in his 2016 book Future Humans: Inside the Science of Our Continuing Evolution. That divergence will start unspooling at the outset, thanks to something called “the founder effect.” No matter how or when it happens, the Red Planet will be settled by a relatively small group of people who are not perfectly representative of the entire human population. For example, it’s a pretty safe bet that Mars pioneers will be atypically adventurous and risk-tolerant. That means, Muskton — the odds are decent that the first Red Planet burg will be named after SpaceX’s CEO — will likely feature more rock-climbing gyms and bordellos per capita than cities here on Earth.

And those initial differences will snowball, because Mars and Earth are very different worlds. The Red Planet is much smaller; the force of gravity on its surface is just 38 percent of the pull we feel here on Earth. Mars also lacks a global magnetic field, a thick atmosphere (though we could remedy that with terraforming), and a protective ozone layer. Mars gets hammered a lot harder than we do by space radiation — UV light and charged particles from the sun, as well as super-energetic cosmic rays zooming in from outside the solar system.

This damaging radiation could cause higher mutation rates in the DNA of Mars settlers, Solomon said. Mutations increase genetic variability, so evolution may proceed faster on the Red Planet than it does here on Earth. What sorts of changes could we see over there? Well, for one thing, natural selection might adjust skin tone on the Red Planet, to help settlers cope with that serious radiation load. (Even if they live in modified caves or lava tubes, as seems likely, the pioneers will still have to spend some time on the surface to tend to their crops and attend spring equinox chili cook-offs, for example.) This may lead to dark skin due to increased production of melanin, just as we see among some peoples here on Earth. But other pigments could potentially be pressed into service as well, including carotenoids, the molecules that give real carrots — as opposed to those purple artisanal weirdos — their color, according to Solomon.

Martian colonists may not be plagued by plagues. The long cruise to the Red Planet could serve as a quarantine, keeping nasty germs from getting a foothold in the settlement.

Mars settlers may also eventually sport thicker bones than their ancestors, Solomon said. That’s because, as research on astronauts in low-Earth orbit has shown, bones become less dense and more brittle in low-gravity conditions. So, Red Planet pioneers with abnormally stout skeletons may do abnormally well, throwing down monster dunk after monster dunk in games of Marsketball while their owned opponents roll around in the dirt clutching their broken femurs and moaning. And Marsketball would be awesome, by the way. If you kept the hoop at the standard 10 feet, all but the most sessile among us could dunk, since you can jump about 2.5 times higher on Mars than you can here on Earth.

And Martian colonists may not be plagued by plagues. The long cruise to the Red Planet could serve as a quarantine, keeping nasty germs from getting a foothold in the settlement, according to Solomon. Muskton probably wouldn’t have to worry about the next Ebola or West Nile emerging from the Martian wilds, which appear to be free of viruses and bacteria, let alone any chimps, birds, mosquitoes, or bats to incubate or transmit them. So, if the settlers left their mammal friends at home — the ones we like to eat, as well as the ones whose bellies we like to rub and ears we like to tousle — they could conceivably banish infectious disease to the memory hole. (The pioneers could go vegan, or eat bugs rather than cows and pigs. Insects are much further removed from us evolutionarily and therefore less likely to pass pathogens.) The settlers’ immune systems might then wither like a snipped umbilical cord, eventually atrophying into vestigiality: White blood cells could be the new tailbones.

“If that were to happen, if, somehow, a disease were to be introduced to Mars, it would be completely devastating,” Solomon said. “That would set up a situation where any contact between Earth and Mars would be extremely dangerous. Steps might have to be taken to basically eliminate any chance of having contact. Even if there are shipments going back and forth, even if there are people going from Earth to Mars, perhaps they don’t ever come into contact with one another.”

This scenario would lead to a cessation of gene flow between Earth humans and Mars humans, and speciation could soon follow.

How soon?

“I hate to ever put numbers on it, because it’s still such a speculative scenario,” Solomon said. “But you’d be talking about at least several hundred to, possibly, several thousand generations.”

This putative outcome doesn’t seem to jibe with our experiences here on Earth, where small bands of pioneers have repeatedly settled new lands without ever diverging into new species of hominid. For example, Native Americans and aboriginal Australians remain in the Homo sapiens fold despite having lived in relative isolation on their newfound continents for about 15,000 and 50,000 years, respectively. But we can take this comparison only so far: North America and Australia are still part of familiar, old Earth, so the environment wasn’t pushing those long-ago explorers to diverge nearly as powerfully as harsh, weird Mars will.

Solomon cautioned that nobody can predict how evolution will proceed in the future. Indeed, some folks have a different take on our relationship with those future inhabitants of Muskton. For example, Mars Society president Robert Zubrin thinks the settlers will develop one or more unique Martian cultures but will not radiate into a new species; they’ll just be too close to Earth, with too much contact. He does think this will happen with interstellar settlers, however, partly because of the inevitable cultural differences that will arise.

“We’re going to have the power, in principle, to control our evolution, to genetically engineer and influence our children,” Zubrin said. “If we have established ourselves in new star systems, in some places, people will probably say, ‘That’s a great idea; let’s do that.’ In others, they’ll say, ‘Oh, that’s immoral. We should not do that.’ So, whether they do it or don’t do it, it’s going to cause divergence.”

Such divergence, he said, could lead to a Star Trek–like panoply of humanoids that differ from each other in just a few trifling respects, such as the color and scaliness of their skin or the number and size of the bumpy ridges on their foreheads. You know, whatever look becomes fashionable on those deep-space outposts, so far from the dominant, original culture and its homogenization machine. Hopefully hipster, skinny jeans won’t make it all the way out to GJ 273b.

Of course, the lack of gene mixing among colonists and their forebears on Earth would be an even bigger factor in our species’ interstellar radiation — if there are still any genes around to be mixed. We may have advanced to cyborg/sublimated consciousness form by the time we start moving out among the stars.

Excerpted from OUT THERE: A Scientific Guide to Alien Life, Antimatter, and Human Space Travel (for the Cosmically Curious). Copyright © 2018 by Michael Wall, PhD. Reprinted with permission of Grand Central Publishing. All rights reserved.