For almost seven years, NASA’s Curiosity rover has been exploring the terrain of Mars. Two weeks ago, it made a stunning discovery: relatively large concentrations of methane gas. The rover also found methane in 2013, but the readings recorded this month—approximately twenty-one parts per billion—were about three times as concentrated. The reason this news registered among scientists is that methane is often a sign of life; although the gas can be produced by various chemical reactions, most of it comes from animate beings. Does this mean that we are on the verge of discovering life on Mars, and, if so, what kind of life is it likely to be?

To discuss these questions, I spoke by phone with Gary Ruvkun, a molecular biologist and professor of genetics at Harvard Medical School. Ruvkun has what he admits are somewhat unusual opinions about life’s origins, and about the possibility of finding life elsewhere. In short, he questions the common assumption that our form of DNA-based life began on Earth. What began as an interview about the methane discovery turned into a discussion about why he wants to send something called a DNA sequencer to Mars. (After our conversation, NASA announced that the methane concentrations had descended back to their usual levels, further confounding scientists.) During our conversation, which has been edited for length and clarity, we also discussed the ways in which scientific debates about the origins of life intersect with religious ones, the reasons he might be dead wrong, and what it feels like to hold a minority opinion in the scientific community.

What is your biggest takeaway from this methane discovery?

Looking for methane is a good method to indirectly look for life. The problem is, there are chemical ways to make methane as well. It is not a perfect surrogate for life. So the way most life-detection experiments are proposed from NASA, especially in this era of exoplanets, where so many planets have been detected around stars, is to do spectroscopic studies of their atmosphere. It is always involving abundant chemicals, like methane and CO 2 .

Do you think that’s the best way to do it? Or are you suggesting that there’s a better way to do them?

It’s the only way to do it with things that are far away. My favorite way to look for life is to go to a planet and look for DNA. And that assumes that life on another planet would be exactly like life here, which is not how most astrobiologists think about things.

How do you think differently about it?

I think viewing life as having started here is a little bit presumptuous. It seems we’re very, very, very special and it all happened here. I find the idea aesthetically appealing that life as we know it is universal across the Milky Way. It just seems like, once it evolves, it spreads. And one way to argue this is running the clock forward instead of running it in reverse. If we’re really talking about colonizing Mars, step one is to send bacteria to Mars to generate an atmosphere. So if you run the clock forward a million years, presumably, we will be sending bacteria to planets a million light years from us.

O.K., wait, I just want to understand this. So what you’re saying is that you find romantic or nice the idea that other life forms would be like us?

Yeah. That life didn’t start here. It just landed here. That it came from somewhere else. And a lot of people complain about that. They say, “Well, then you’re just putting the problem of origin of life somewhere else.” Which is true.

In an e-mail to me, you referred to your views as “not very standard for microbiology.” And this is partly because you want to send a DNA sequencer to Mars, yes?

Here on Earth, if you go to some lake or a forest and want to know who lives there, the current method of choice for figuring out who’s there is to just take dirt, make DNA, and do all the genome sequences inside that DNA. And you get a pretty good fingerprint of who lives there. And of course there’s a lot of different kinds of bacteria that live in soils and things like that.

And, if you look in the literature, there are tens of thousands of papers now that do that, and it was done the first time maybe twenty years ago, using DNA as a kind of signature to look for living things. So we would say, “We’ll just do that on Mars and do the sequence.” And you could ask, “Well, do you find anything there that looks like it’s our cousin?” It doesn’t have to be our brother. It can just be more distantly related than a brother, but a cousin, and therefore coming from the same tree of life. Once you do that, you can say, “Oh, well, life on Earth and Mars is similar, and that’s sort of the least-interesting idea, because Earth and Mars are right next to each other.” So it’s kind of almost obvious that they would share the same kind of life, because there’s an exchange. But what if it actually is the entire Milky Way that has the same life?

What would people who are skeptical of the way you’re thinking about it say in response to this?

They’d say that’s just stupid. [Laughs.] Because they’re saying, “Well, it had to start somewhere, and so why would you not think it started here? Why are you positing that we caught life instead of evolved it?” Because there’s clearly evidence for how life evolved in our genomes. It’s what’s called the RNA World, which was kind of the earliest form of life, and is still present in our genomes. We can see it there, and so you can discern early steps in evolution just by looking in modern genomes. In orthodoxy and all the textbooks, the RNA World—that’s kind of the precursor to the DNA world—was here on Earth four billion years ago. And I would propose, no, it was probably ten billion years ago, somewhere on the other side of the Milky Way, and it’s been spreading all across the Milky Way.

So the four-billion-year and the ten-billion-year estimates—there is no scientific basis for either estimate? Is that what you are saying?

No, no, no. The Earth is 4.5 billion years old. And the universe, at least based on estimates from the Big Bang, is something like fourteen billion years. So, if life evolved somewhere else, that buys you about ten billion years of time. But I’d rather it bought you a hundred billion years of time or a thousand billion years of time. That would be more satisfying.

Why would it be more satisfying?

Well, because it allows more time. See, the thing is, if you look in the fossil record, where’s the first evidence of life? Well, you can see evidence of bacterial life, things that look like bacteria, the things that are called stromatolites, which are a kind of blue-green algae bacteria that live in colonies. Those things form good fossils, and you can see those about three and a half billion years ago. So, life had already evolved to the point of there being pretty complicated bacteria very quickly, after the Earth cooled.