Human evolution is a story writ slow. It’s been about 3.8 billion years since life on Earth emerged and steadily began to spread its reach from the tidal pools to the oceans to the shorelines to the grasslands to the forests—and, ultimately to New York and Tokyo and Shanghai and more. Having exhausted our terrestrial destination, humanity is now reaching for extraterrestrial ones. Our dream of going back to the moon and onto Mars and more distant worlds—not least to ensure our species’ survival before the sun flames out and engulfs most of the solar system—can be seen as just one more step in evolution’s long march. That’s the compelling argument made by Caleb Scharf—author and senior scientist for astrobiology at NASA Ames Research in Moffett Field, Calif.—in his new book The Giant Leap: Why Space Is the Next Frontier in the Evolution of Life. Scharf sat down with TIME to talk about life, survival, and the fate of our species.
TIME: Much of what you write about in the book involves the idea of “dispersal” as an evolutionary process that could dramatically change the human species. Describe what you mean by that.
Scharf: Dispersal refers to the idea of life spreading far, far beyond its point of origin. It’s the same kind of process that we see play out on the Earth where a species migrates to some new environment and then undergoes changes. A single species becomes many species because its descendants necessarily adapt to environments that they find themselves in. The sheer scale of the landscape in which a spacefaring species will find itself must change it. It will cause it to speciate. It will cause it to become maybe multiple species.
We evolved to live here, on Earth, and yet we’re trying to live there, in space. Isn’t this maladaptive?
We could look at the history of life on Earth and say, “Well, life did really, really well in the oceans. Why would you have surface plant life eventually evolving?” Of course, there’s no plan. Evolution is a process of continual experimentation. And so my perspective on this is that, yes, it seems hideously awful to try to exist in space or even on the surface of another world like Mars. But I think technology is an adaptive trait, just as other organisms construct things around themselves—termites build nests, birds build nests, animals manipulate their environment to make it more suitable for themselves. We do this as well.
If Earth is ultimately doomed—if the sun will begin to incinerate us in about a billion years—Mars wouldn’t do as a safe harbor, since that planet would be put to the torch as well. The answer is to go to other star systems, but unless we can break the laws of Einsteinian physics, we could never approach the speeds needed to reach even the closest stars in a human lifetime. So are we doomed?
I think the answer is very uncertain. Any reasonable mechanism we know of now to get to another star is going to take a long time. We know chemical rockets won’t do it. Light sails and giant lasers might get you some of the way there. And there are other ideas to do with ion drives and collecting interstellar gas and using that to propel yourself along—but all that would involve very lengthy trips. Maybe that is a barrier that all biological life eventually comes up against. And perhaps one reason we feel so alone in the universe is that nobody else gets through that particular barrier.
You write that space exploration wouldn’t be possible without “the ecosystem of mathematics, physics, and chemistry” that have developed over the past couple thousand years. Is that ecosystem a function of evolution or a cause of evolution?
I suspect that it’s both. Human-like intelligence as far as we know has only been around for a few hundred thousand years. We don’t know exactly how smart the Neanderthals were, but we could speculate that we had a similar scope of intelligence. The sobering thought is that it may be too early to know whether that emergent trait has a positive or negative effect on survival.
The Apollo 11 moon landing was a hinge point in human history, as you describe in the book. But we have not been back to the moon since the end of the Apollo lunar program in 1972. Why are we stalled on Earth?
I would say that in some ways, we’re not stalled at all. Certainly human exploration beyond Earth orbit ground to a halt after Apollo. But the rest of space exploration has just barreled ahead. The Apollo missions were designed and constructed to get the job done, which was to accomplish what [President] Kennedy laid out on the table, for all its geopolitical value and its bragging rights and so on. The problem with that kind of enterprise is that you’re not necessarily thinking long term. That doesn’t really set you up for long term success.
There are millions of species on Earth. If we’re going to get off the planet before the sun burns out, do we have an evolutionary responsibility to take some of them with us?
We would inevitably have to take other life with us. Obviously, there’s the human microbiome; that will go with us. And we have to think about whether we need to take elements of the microbial environment that surrounds us because the microbes that live on the surface of everything in the world also contribute to [our well-being]. We also need to eat and I think we would inevitably take a certain number of species with us, selfishly because of food. I’ve been asked about this before and I’ve said I would take a cubic kilometer of the Earth’s surface and everything in it—all the bugs, all the creatures, all the plants, all the microbes. I would just dump that in a container and use that as part of my life support system.
There are currently more than 8.1 billion of us and that number is only likely to grow in the future. If the time comes to cast off from Earth, we’re certainly not going to transport billions of people. Will this be a melancholy waving goodbye to a selected few hundred thousand while the other billions stay behind and perish?
Realistically, any future like this will play out over such a long time scale that it would be more an instance of a gradual sort of rebalancing. Over a century, maybe a few thousand humans—pioneer organisms—go out and start living in a hollowed out asteroid or elsewhere. And gradually, you know, there’s growth. People born many generations after us will perhaps have the option to decide, do I want to stay on Earth, or do I want to go somewhere else? I don’t know what their choices would be.
Do you think we can ever overcome our tribalism sufficiently to do this collectively?
It depends on what day you ask me that.
Are you optimistic or pessimistic about humanity’s future?
[Laughs] It depends on what day you ask me that.
