If humanity ever travels to another star, the trip could take generations. Such a journey would present serious technological challenges, of course, but the social difficulties of keeping a large population happy and healthy on a spaceship could be no less daunting. Anthropologist Cameron Smith of Portland State University has studied these questions and will discuss the biological and cultural science of long-term space travel during a lecture at the Perimeter Institute for Theoretical Physics in Ontario that will be broadcast live here on this page.

Smith’s talk, “Interstellar Voyaging: An Evolutionary Transition,” will begin Wednesday at 7 p.m. ET as part of the Perimeter Institute’s public lecture series presented by Sun Life Financial. The lecture will be viewable on this page as well as at http://www.perimeterinstitute.ca. Online viewers can pose questions to Smith by tweeting to @Perimeter and using the hashtag #piLIVE.

Scientific American spoke to Smith about what it will take to mount an interstellar voyage. Below is an edited transcript of the conversation.

Is it really plausible to discuss a multigenerational space journey? Are we even close to being able to do something like this?
I’m presuming that the physics people will give us high-speed propulsion. I’m playing the same game as [space research organization] Icarus Interstellar. Their project is not to build anything now. They want to give humanity the option at the end of this century, in a hundred years from now, of interstellar voyaging. I think that’s a smart approach. It’s a mind-boggling thing to imagine, but so was going to the moon 100 years ago.

I think it’s a very good idea to start thinking about it now, and to spend a century thinking about the genetics, the cultural implications, the propulsion and designs. I think it’s possible, but I think it should be done carefully. I don’t want to see a brief flurry of interest and then see it flare out—the American moon program did that.

One of your first projects in this field was to research the population genetics of a space colonization journey. What did you learn?
If you’re going on multigenerational voyages and you have a closed population, you don’t have the natural interbreeding links that all human societies have. We have good evidence that human populations need to be well over 5,000 and into the tens of thousands of people to maintain healthy genetic variability. I suggested recently in a paper that 40,000 is a safe number.

People have proposed that you could send fewer human beings and store frozen eggs and sperm and maintain viability that way. But there are cultural reasons why that’s not so great. I think we should go in populations that are culturally familiar. In evolution, generally speaking, radical changes in the short term are not too typically likely to work. And so I would propose a larger starship with tens of thousands of people aboard and let them sort out the new variety of social and genetic interactions that need to happen as they’re going. Don’t try to invent it all here.

What are the other human evolutionary challenges associated with such a voyage?
It’s largely going to be developmental genetics in non-Earth environments. When we think of space biology now, we tend to think of adults. But I’m thinking about the developmental biology of the young.

We also tend to think of how it’s done in low-Earth orbit, in microgravity, but that environment is so alien to the whole human experience that I don’t think that gravity environment is realistic to think about on a long-term voyage. Even on Mars it’s only one-third the gravity of Earth. You’ll also probably have a different breathing-atmosphere composition—probably higher oxygen content. This has to do with the pressure you have to maintain. So let’s say we have a slightly higher oxygen percentage—what’s the effect on the human body? That’s a big one.

If we could launch an interstellar trip now, would you go?
For just the sheer experience of being part of an evolutionarily significant event for Earth life, yes, it would be fantastic to go.

But it would be easier if I were married. I think it’s a very good project for family people. I’ve stayed by myself, I’m awfully busy, I’ve decided to pursue academic and other things, and I think it would be a lot easier for a person who has a family to consider going. You can still imagine your continuation through your children.

I’m surprised by that. For many people, getting your spouse to agree to go and deciding to put your family at risk could be the main barriers to making the trip.
There is a really interesting moral argument against this, which is that you can’t subject unborn people to this environment. But there was a philosopher who concluded that in these environments, if you’re making this interstellar voyage and you’re preparing the whole system of food for multiple generations, in fact those children will be born into conditions that are much more stable and much more likely to provide a good life than most people on Earth are born into. So I think I buy the argument that it is morally acceptable to do it.

In fact, I think it’s a moral imperative. To not look at and explore the universe around us, that’s indefensible. People assume the Earth is safe, just because it’s been a great place to live since the advent of farming. But geology shows us there have been five big extinction events in Earth’s history. So I think it’s morally acceptable to send people on these voyages, and I don’t think you’d have any problem finding volunteers.

With the recent movie Interstellar, and what’s going on in spaceflight now, it seems like there is a lot of popular interest in interstellar travel and space colonization these days. Why do you think that is?
From an anthropological perspective, I think it’s an inevitability that people will try space colonies. [SpaceX founder] Elon Musk’s stated goal is the settlement of Mars. Right now it’s big in the American consciousness. It’s also there because we are in this second space age now, where I don’t know how many startups are looking at commercialization of space access. That’s important—the easier and cheaper we make it to get to space, the sooner we can get on with exploring the universe beyond Earth. We also have the new science of exoplanets that gives us places to think about visiting.

If you’re thinking about doing this, every aspect of life has to be considered, because it’s human populations in a completely new environment. So that’s one reason why it can be quite exciting to people. If we ever have a Mars colony, it’s not a mission anymore. It would just be living out your life. And so we have to have a cognitive shift on how we think about this, from short-term to long-term, and from individuals in space to families in space, and communities and larger cultures.