Darwin in Space: How Multigenerational Missions Could Shape Human Evolution

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“New environments inside this starship, for example, new radiation environments, whatever the gas composition is that people are breathing, whatever is the gravity field, those basic environmental conditions will reshape the human genome.”

That’s Cameron Smith. He’s an anthropologist at Portland State University who studies human evolution and prehistory. But he’s also very interested in the human future, including how space travel will impact the human race—both culturally and biologically. He wrote an article on the subject in the January issue of Scientific American, called “Starship Humanity.” He recently talked by phone with John Matson, host of our 60-Second Space podcast, about what might happen to a spacefaring humanity if we really were to take a star trek.

John Matson: This article that you’ve written for Scientific American, maybe you can just give us a brief overview of what the article is about.

Cameron Smith: You bet. So far the experience of humanity in space has been very limited. We have gone up for short periods of time, we’ve gone in very small numbers. But as space access becomes cheaper and more people start going up, eventually we’re going to have communities, we’re going to have populations of people up there. And then it shifts, our understanding of that is going to have to shift from purely biology to anthropology. These will be communities of people, and of course communities are cultural and they’re also biological. So anthropology marries culture and biology. And it will be used to help us plan out successful space colonization.

JM: Let’s say, just to set a scenario, a group of space travelers sets out on a multigenerational voyage to Alpha Centauri, where we now know that there is an exoplanet. What’s going to happen to these people on the way?

CS: Well, we can only predict that change will occur. We can make some predictions about some very few biological changes that might occur. But because mutation is random, and mutation is the origin of new characteristics in populations, because that is ultimately random, it’s not entirely possible to say precisely what 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. Subtly, subtly, but they will reshape it.

We know that we have evolved under almost 15 pounds of pressure per square inch at sea level. And in the last few thousand years, though, some people have migrated to higher elevations, where they are under somewhat less pressure. Their biology has changed to account for that, or to make it possible to live there. They have different blood oxygen levels, they have deeper chests with greater what is called lung ventilation, greater capacity for breathing in and taking in oxygen. And even the biology of the developing infant is somewhat different. And I am certain that exactly the same sort of thing, on that same magnitude, will happen in off-Earth environments.

JM: What about weightlessness? Do we have any sense of what that would do to human physiology in terms of stature or size of human beings?

CS: Weightlessness is a big issue, and 30 years of almost continuous presence of humans in space—this is quite amazing—whether in Mir or the International Space Station or other stations, for 30 years somebody has been in Earth orbit almost continuously. What they have learned through that long period is that, yeah, weightlessness can have some pretty detrimental effects. Bone loss is one of them. Muscle is also reduced, but bone loss is a big one.

And so, I don’t think we’re going to try to do long-term space colonization in free-floating zero gravity. So we’ll go to places like Mars where there is one third, roughly, the gravity of Earth, and I think we’ll build these things that rotate and give us artificial—well, they give us gravity by rotating. You saw it in 2001: A Space Odyssey, the rotating space station. That works, and I think we’re going to be doing that for a much longer time than trying to actually live in zero or very small gravity.

But yes, it will have effects on the physiology as well. I was thinking of course in Mars, at one third, roughly, gravity, essentially in evolution, essentially if you can get away with something that costs less energy to do than your sibling, you have a selective advantage. And on Mars if you don’t require all of the muscle that a person does on Earth, where you have an extra two thirds gravity, then presumably you live in better health and have more offspring. So in the long term on Mars I think we will eventually see a lighter, lither build than on Earth.

JM: So the image of those spindly little green men is maybe not too far-fetched.

CS: Maybe so.

JM: Now, do we have a sense of how quickly these changes start to happen?

CS: The time scale for significant biological changes—yes, you can get them in a few centuries. You can start to see effects on the physiology in a number of centuries. This is the timescale that I’ve been working with. For example I’m in contact with a group in Germany called Icarus Interstellar. They’re devising propulsion systems to reach stars on the scale of several centuries. So I’ve been thinking about that scale as well—what kind of changes would we see in that kind of time frame? And some basic population genetics calculations that I’ve done, that concern what’s called time-to-fixation, and this is the spread of novel genes in a population.

And this suggests that yes, within a few centuries you could have changes on the order of different skin hues, or altered skin colors, different hair textures. But radical reshaping of the human body, for example. major stature differences or even new anatomical structures, those should take much, much longer. Those should take into the many thousands of years.

JM: There’s definitely a perception, especially in this country, in the U.S., that space exploration is on pause, that it’s ground to a halt. I happen to disagree with that, but it’s clear that no one is going to Alpha Centauri tomorrow. So why is it important to consider all these things now? Why is it important to think out all the implications of what space travel might mean?

CS: It’s absolutely important to start now because there’s so much to do. I mean, if we’re talking about long-term voyages, we’re talking about again, understanding things that we are just barely understanding today. For example, we have only in the last two decades got a high-resolution understanding of the human genome. And that helps us to understand human evolution, and evolution, it cannot be stopped. The only way to stop it is with extinction. And evolution of humanity is going to continue in space. And to prepare for it—again, you could do it without anthropology, but I don’t think it would survive. I don’t think it would work. So to do it with a good expectation of success, we need to think in long term. Well, what is the field that has given us a long-term understanding of humanity? That’s anthropology. Biology, relatively short-term, although it deals with evolution. But humanity, human evolution is somewhat different from most other evolution. And it's anthropology that has explored that. So, I think anthropology is going to be central to this.

JM: So as the physicists and engineers are working on propulsion systems and cosmic ray shielding, this is something that anthropologists should be working on in parallel, you believe?

CS: I believe absolutely we need to build an anthropology of space, an anthropology of space colonization. We know if we're going to spend generations in space that you have to prepare for the long term. Again, we think of it as people pop up there and they come back down. And the long-term view is, no, eventually, this will be migration. And this is part of the goal. Even just a few years ago NASA had a Vision Report that they released, which said that the essential mission of NASA was to better life here on Earth, to extend life there, that is, move some part of humanity to be able to live off of earth, and to find life beyond, that is exobiology. The interesting thing there is that in common in all three of those, what is common about those, it's not computers, it's not the technology, you need all of that, but what is common about those three statements is that it's about life. It's about living things. And living things change through time by evolution, and it's anthropology that has understood human evolution.

JM: You have a fairly recent book out about evolution.

CS: I have a book out now, a Popular Science book about human adaptation and space colonization, and in that my co-author and I are sketching out, it's an exploration, we're sketching out some of the kinds of ways that anthropology can assist us in making a success of space colonization. But right now I'm working on a technical book, it'll be a couple of years down the line, that again brings everything pertinent known from anthropology to the concept of space colonization, and hopefully that can be a foundation for a space anthropology.

JM: Now just to sort of wrap things up here, aside from the physics and the engineering of the actual spacecraft, what do you think will be the biggest challenge facing either the people who are putting together a crew for a long-duration spaceflight, or for the crew themselves?

CS: Well, one critique of this whole endeavor of space colonization and space activity by people in general is that, well, this isn’t going to fix humanity. We’re just going to transport our ancient problems off of the surface of the Earth. Well, I think so. Yeah, this isn’t meant to fix humanity. It is meant to give humanity an insurance policy. If the Earth is hit by a catastrophe, at least someone is left, if we are a several-planet species, for example.

The biggest challenge, I think they’ll be both biological and cultural. We don’t know how reproduction works in space. We also have to be very careful—we can’t just be ready to go and colonize space once we understand human biology in space and human evolution. We have thousands of plant and animal domesticates that are going to have to go with us. We can’t be eating canned food for generations. We have to ensure the health of those populations as well. That is why, you asked before, why start now? Well, there is a tremendous amount to do to think about all this.

So what will be the challenges? They will be both biological and cultural. We will have biological evolution happening—some of it will be painful. Much of that evolution will play out on those early stages of development. And there will be an increase, let’s say, in infant mortality. We’ll also have our same cultural baggage. We have ethnic rivalries, we have political differences, we have religious issues. I don’t think that’s going to go away. We should certainly take our best nature with us, but those things are rather ancient, and I think those will be as big a challenge as the biology.

Cameron Smith’s book, co-authored with Evan Davies is titled Emigrating Beyond Earth: Human Adaptation and Space Colonization. And Smith’s article "Starship Humanity" is in the January issue of Scientific American. A short preview is available free on the Web site, titled "How Humans Will Evolve on Multigenerational Space-Exploration Missions."

That’s it for this episode. Get your science news at our Web site, www.scientificamerican.com, where you can check out the In-Depth Report about Humanity’s Enduring Fascination with the Apocalypse. The so-called Mayan apocalypse is just the latest in a long line of doomsday predictions. And, ironically, it will not be the last. And follow us on Twitter, where you’ll get a tweet whenever a new article hits the Web site. Our Twitter name is @sciam. For Scientific American’s Science Talk, I’m Steve Mirsky, thanks for clicking on us.