Escaping Earth as a Sign of Intelligence

Avi Loeb
6 min readSep 4, 2023


A cereal box cover shared with me by the Israeli writer, Dror Burstein, from his trip to London (September 4, 2023)

It is arrogant of us to believe that we are the most intelligent species that ever existed in the Universe since the Big Bang. Not just because there are billions of Earth-Sun analogues within the Milky-Way galaxy alone. But also because many past civilizations might have perished by now as their Sun-like star became a white dwarf. Hence, the only way to learn about them is not by searching for their radio signals but by searching for the packages they sent to interstellar space, as discussed in my new book Interstellar. Most scientists have an opinion on this matter but few are willing to invest time and resources in the archaeological search for such relics.

The tendency to look for excuses as to why not search is pervasive. This was illustrated by an email I received this morning, which read:

“Dear Doctor Loeb:

I’ve just started reading your wonderful new book (“Interstellar …”) and your discussion of extraterrestrial civilizations reminded me for some reason of a description by Noam Chomsky of a debate between Carl Sagan and biologist Ernst Mayr. Mayr’s assertion that intelligence may be a lethal mutation is (to me) both shocking and somewhat compelling.
Here’s how Chomsky described the debate:

“I’ll begin with an interesting debate that took place some years ago between Carl Sagan, the well-known astrophysicist, and Ernst Mayr, the grand old man of American biology. They were debating the possibility of finding intelligent life elsewhere in the universe. And Sagan, speaking from the point of view of an astrophysicist, pointed out that there are innumerable planets just like ours. There is no reason they shouldn’t have developed intelligent life. Mayr, from the point of view of a biologist, argued that it’s very unlikely that we’ll find any. And his reason was, he said, we have exactly one example: Earth. So let’s take a look at Earth.

And what he basically argued is that intelligence is a kind of lethal mutation. And he had a good argument. He pointed out that if you take a look at biological success, which is essentially measured by how many of us are there, the organisms that do quite well are those that mutate very quickly, like bacteria, or those that are stuck in a fixed ecological niche, like beetles. They do fine. And they may survive the environmental crisis. But as you go up the scale of what we call intelligence, they are less and less successful. By the time you get to mammals, there are very few of them as compared with, say, insects. By the time you get to humans, the origin of humans may be 100,000 years ago, there is a very small group. We are kind of misled now because there are a lot of humans around, but that’s a matter of a few thousand years, which is meaningless from an evolutionary point of view. His argument was, you’re just not going to find intelligent life elsewhere, and you probably won’t find it here for very long either because it’s just a lethal mutation. He also added, a little bit ominously, that the average lifespan of a species, of the billions that have existed, is about 100,000 years, which is roughly the length of time that modern humans have existed.

With the environmental crisis, we’re now in a situation where we can decide whether Mayr was right or not. If nothing significant is done about it, and pretty quickly, then he will have been correct: human intelligence is indeed a lethal mutation. Maybe some humans will
survive, but it will be scattered and nothing like a decent existence, and we’ll take a lot of the rest of the living world along with us.”

I have to admit that at age 81, I’m keenly aware of how close I am to the end of my life, and yet I fervently wish I could be here when some of the evidence you expect appears! Reading your book gives me hope.

I’d be interested to know whether Mayr’s point dampens your optimism at all?


My reply was that as an intelligent species we can avoid the limitations imposed on us by zero-sum games on Earth. Mayr’s argument is interesting since according to a new paper in Science magazine, the human population included merely 1,300 breeding individuals about 0.9 million years ago.

But in contrast to other species, human intelligence allows us to escape the limitations imposed by the terrestrial habitat. If our technological civilization will manage to launch self-replicating space probes equipped with 3D printers and AI, then Mayr’s fatalism will not apply, because these devices would propagate beyond the historical limits imposed on species which stayed on Earth. Technology can be regarded as an extension of nature, capable of reaching grander horizons than available to non-technological species. Even if humanity will be fatally injured by self-inflicted wounds on Earth, its technological probes could make their way to interstellar space and outlast the Sun for billions of years.

We can be inspired to explore interstellar space by finding others who did it billions of years ago. This motivated the successful expedition I led to the Pacific Ocean in search for the molten droplets from the surface of the first recognized interstellar meteor, IM1, which exhibited anomalous speed and material strength — in analogy to our own five interstellar probes.

The technological ability to intentionally travel out of a habitable planet rather than wrestle with its limited resources, is a unique signature of an intelligent species. It constitutes an important distinction that can grant humanity longevity well beyond any other species which is limited to its home planet.

Our biggest enemy is not biological fatalism but rather the psychological chains we impose upon ourselves by not seeking a more ambitious future in interstellar space. In the cosmic scheme of things, natural selection favors species which leave their planet and prosper in other locations.

Finding packages from those successful species may inspire us to do the same. This is why we must check our mailbox for any packages with an extrasolar postal address. Gladly, some scientists recognize this insight, as indicated by the second email I just received from a fellow astrophysicist:

“Hi Avi,

Congratulations on your exciting and successful expedition! I enjoy following along your research, writings, and media interviews. You are doing a good thing for science by demonstrating the value of taking risks and following your curiosity. There is no one way to be a scientist and it’s very valuable for the community to take a diversity of approaches and also see those approaches in action.

You are helping improve culture too. It surprises me how conservative academia can be when it comes to research ideas, and how the incentive structures are not quite designed the right way to encourage the best set of actions for scientific discovery and advancement. So, it is inspiring to see you break the mold.

I’m excited to follow along and see where your research program uncovers. Best wishes,”

Our chemical rockets could reach the other side of the Milky-Way galaxy over a timescale of a billion years. According to the star formation history of the Universe, most stars formed billions of years before the Sun. Those who benefitted from an earlier technological start could have reached our mailbox by now. Here’s hoping that an inspiring message awaits us in our mailbox.


Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He chairs the advisory board for the Breakthrough Starshot project, and is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. His new book, titled “Interstellar”, was published in August 2023.



Avi Loeb

Avi Loeb is the Baird Professor of Science and Institute director at Harvard University and the bestselling author of “Extraterrestrial” and "Interstellar".