 |
By Adam Frank
Life on Earth has made several “great leaps” in its evolutionary history: from unicellularity to multicellularity, from sea to land, and from land into the skies.
What if the next one lies beyond our planet? That’s the question behind Caleb Scharf’s latest book, The Great Leap: Why Space Is the Next Frontier in the Evolution of Life, which explores how cosmic evolution and human technology are shaping the next phase of life’s story.
Scharf is an astrophysicist, astrobiologist, and author whose work bridges science, philosophy, and the future of humanity. He serves as Senior Scientist for Astrobiology at NASA’s Ames Research Center and is a recipient of the Carl Sagan Medal from the American Astronomical Society.
I’ve known and collaborated with Caleb for a while, and I’m always inspired after talking with him — he’s the kind of person who thinks on a large scale. We recently sat down (over Zoom) to discuss his new book and its themes.
Adam Frank: Your new book, The Giant Leap, argues that life pushing into space marks a fundamental evolutionary transition. Let’s start there: What makes something a “major transition” in evolution, and why does becoming a spacefaring civilization qualify?
Caleb Scharf: The way I think about major transitions in life’s history is that they’re moments when the rules change — when new kinds of possibilities open up. Each one transforms how evolution proceeds.
Take oxygenation, for example. When photosynthetic organisms started releasing oxygen into Earth’s atmosphere, it radically expanded what life could do. It unlocked new biochemistry, new energy sources, new ways for organisms to exist. Multicellularity is another one: Suddenly, organisms could build internal environments, cooperate, form symbioses. Life could modify itself and its surroundings at a much larger scale.
Those transitions didn’t just add more species; they opened new realms of possibility. That’s what I think going into space represents. It’s not just humans with rockets — it’s life reaching beyond the planet that gave rise to it. That act creates new niches, new environments, new selective pressures. It changes the possibilities for what life is and can become.
Frank: So you’re saying this isn’t just a human project — it’s a biospheric one.
Scharf: Exactly. Obviously, it’s humans who are doing it right now, but the deeper process is biological. Life on Earth has always been an experiment in expansion. It fills niches and creates new niches. It does that on every scale — from microbes altering local chemistry to forests transforming the atmosphere.
So when life, through us, starts reaching beyond Earth, that’s the same impulse playing out on a larger stage. The details — the Cold War, the military-industrial complex, Elon Musk — those are the surface-level expressions. But underneath, it’s life doing what life does: extending itself into every possible environment.
Frank: I love that reframing. I always like to say, if we settle Mars, it won’t really be humans doing it. The biosphere will really be the agent reaching out with its green tendrils. But this does raise serious ethical questions. Some people argue that Mars — or any untouched world — should remain pristine, a kind of cosmic wilderness. How does your view respond to that concern?
Scharf: It’s a tough issue. On one hand, I have a lot of sympathy for that argument. I don’t want to see us “pollute” Mars just for the sake of saying we’ve been there. There’s something sacred about untouched worlds.
But on the other hand, I think the deeper reality is that this expansion is going to happen — because humans are not a monoculture. Some people will always push boundaries. You can’t legislate curiosity or ambition out of the species. So the question becomes not whether it will happen, but how we can do it responsibly.
In the book, I talk about what I call a “fourth path” for Mars exploration — rethinking exploration itself. We still imagine exploration as a 19th-century enterprise: pack sandwiches, march over the hill, and claim what you find. But our technology has changed that paradigm completely.
Frank: Yes, on the sandwiches. You must pack sandwiches.
Scharf: But today, we can map entire planets from orbit, collect petabytes of data, and model environments we’ve never set foot on. We can start by building a deep, systemic understanding of a world before we physically alter it. That’s a kind of planetary exploration that’s informational rather than extractive. And that’s where the ethics come in — we can learn, adapt, and maybe even prepare for coexistence before we invade.
Frank: So you’re arguing for a kind of preemptive awareness — a way of extending life without repeating the old mistakes that every expanding civilization did in the past.
Scharf: Exactly. We can’t romanticize space as a “pure wilderness” forever, but we can evolve our methods. We already use satellites to understand Earth in unprecedented detail. Why not apply that same approach to other worlds? Build the infrastructure of knowledge first.
That kind of exploration not only minimizes harm but also maximizes what we learn. It could even make human presence on Mars safer and more scientifically productive when the time comes. And the insights we gain will feed back into how we live on Earth. Every time we learn how to sustain life in an extreme environment, we learn more about sustaining life here.
Frank: That takes us to another idea you explore in the book: humans as catalysts. You describe us as technology-bearing agents of biospheric transformation. But becoming an interplanetary species is an enormous challenge. What are the biggest barriers?
Scharf: There are several, but they all boil down to energy and biology. Nature never evolved a way for living things to reach escape velocity — 8 to 11 kilometers per second — because that’s not something a biological organism can do on its own. So this is where analytic intelligence comes in. Humanity, for the first time, built the tools to overcome gravity’s cage.
Frank: “Gravity’s Cage”… that’s a great phrase. I’m going to use that.
Scharf: That’s the first barrier: the sheer physics of leaving the planet. But we’re getting better at it. Seventy years ago, rockets blew up more often than not. Now we’re on the verge of launching daily from multiple sites around the world. That persistence — iterative improvement — is how evolution works, too. It’s technological evolution mirroring biological evolution.
The second barrier is sustaining life away from Earth. We’ve had humans in orbit for decades, and we’ve learned how hard it is. Radiation, muscle loss, psychological strain — it’s all complex. But every mission teaches us what the problems are, and that’s the first step to solving them.
So I don’t think there will be a single breakthrough moment. Instead, it’ll be gradual: private space stations, lunar bases, maybe stations around Mars or its moons. Each step builds a little ecosystem, a little economy, that’s increasingly independent from Earth. That’s how you bootstrap an interplanetary civilization.
Frank: And that civilization might eventually have more life beyond Earth than on it?
Scharf: Potentially, yes. If you look at the resources available in the solar system — the mass, the energy — they far exceed what’s on Earth. If life fills those niches, even partially, you could end up with trillions of organisms — humans, machines, hybrids, biospheres of all sorts — spread across thousands of habitats.
That’s when you really start to see the “giant leap” as evolutionary, not just cultural. Life begins to decouple from its planet of origin. The biosphere becomes a heliosphere — a distributed network of living systems using solar system resources. That’s an enormous conceptual shift. It’s not science fiction; it’s the logical extension of life’s four-billion-year story.
Frank: It’s interesting how that logic makes expansion seem inevitable. But what about timescales? When do you think we’ll actually see large-scale habitation beyond Earth?
Scharf: Predicting the future is always risky, but if you force me to guess — I’d say centuries, though maybe not many centuries.
It could even be within one. Look at population growth. In the mid-1800s, there were about a billion people on Earth. Now we’re over eight billion. Technological and social transformations can accelerate rapidly once they reach a certain threshold.
The same might be true for space. Technologies like 3D printing, algorithmic design, in-situ resource utilization — those change the economics. You no longer need to haul an entire industrial base into orbit. You can build what you need locally, from available materials, with far less infrastructure. That’s a profound shift.
So while I think it’s centuries before the number of humans off Earth rivals those on Earth, exponential change has a way of sneaking up on us. Once the curve steepens, things move very fast.
Frank: That’s true. I always point out to my class that 200 years ago, no one had ever traveled faster than 60 miles per hour unless they were falling off a cliff. Now we routinely send machines past the edge of the Solar System. What I love about your framing of this question is that it puts humanity back into a cosmic context. We tend to see ourselves as the end point of evolution, but you’re saying we’re just another stage in a longer process.
Scharf: Yes. I think that’s the humility we need. Humanity is extraordinary, but not exceptional in the cosmic sense. We’re part of life’s ongoing project of self-expansion and self-awareness.
The Giant Leap isn’t about human destiny so much as life’s persistence. Evolution is opportunistic. It uses whatever tools it can find — DNA, photosynthesis, neural networks, silicon chips — to keep the experiment going. We’re one of those tools. The rockets, the computers, the telescopes — they’re all extensions of biology’s capacity to reach further.
And that, to me, is profoundly hopeful. Because it means that the story of life isn’t [bound] by Earth’s lifespan. It’s just beginning its next chapter.
Frank: You know, that sounds like the ultimate long view — the Universe itself becoming aware of its potential through the life it hosts.
Scharf: Right. Consciousness, technology, exploration — all of it may be the cosmos finding ways to look back at itself. In that sense, going into space isn’t escape — it’s introspection on a cosmic scale.
And maybe that’s the most important part of the giant leap: not just that life expands outward, but that it learns to understand itself as a planetary and interplanetary phenomenon. Once you see that, you can’t unsee it.