If humans went extinct, could we re-evolve?

On a tiny atoll in the Indian Ocean, there lives a flightless bird called the Aldabra rail. It looks unassuming enough — brown feathers, chicken-sized, and incapable of flying.

Roughly 136,000 years ago, its ancestors — white-throated rails from Madagascar — flew to Aldabra and found a predator-free paradise; no sharp-toothed prowlers or featherless bipeds with pointy sticks. And so, the rails evolved into flightless versions. Why waste effort and energy on flying when there’s no point?

Then came a catastrophic flood. The island went underwater. The rails couldn’t fly, and they couldn’t swim. They went extinct. And then, after the seas receded, something eerie happened. More rails flew back — their distant ancestors, still strong in Madagascar, made the same flight again. And the story repeated itself. The rails lost the power of flight and remained island-bound. Scientists studying the fossils have confirmed this wasn’t just a similar bird doing a similar thing. It was the same lineage, re-evolving nearly the same bird.

This is what biologists call “iterative evolution” — when evolution plays the same song all over again.

In this week’s Mini Philosophy interview, I spoke with philosopher Toby Ord, author of The Precipice: Existential Risk and the Future of Humanity, about extinction events and the likelihood of a species-wide human extinction. One of the questions we explored was whether humans — or something human-like — could re-evolve if the worst came to the very worst.

A history of iteration

Beyond Aldabra, fossils show other instances of iterative evolution. Certain sea turtles, for example, independently evolved seagrass-munching adaptations multiple times across different epochs. Climate and habitat changes mean that turtles in one area would sporadically go extinct, only for similar adaptations to re-evolve when the habitat changed back. Long, paddle-like limbs. Flat, crushing jaws. Each time the oceans offered up the right environment, evolution sent out another turtle to graze.

Evolution selects for genes and genetic capabilities that are the best fit for an environment. So it makes sense that over the course of billions of years, the same traits will pop up. If we look at things on evolutionary timescales, the world’s environment kind of oscillates between extremes — cold and wet, then hot and dry. An ice age leads to an ice thaw. Low water levels give way to high water levels. And so, the species that occupy the various environmental niches will likewise have to oscillate. The species of the world today are the best fit for the environment we currently have.

These aren’t clones. They’re evolutionary rhymes. Variations on a theme. Familiar silhouettes drawn by different hands.

Given the sheer numbers involved, there are no known examples of species re-emergence. The Aldabra rails were still the same bird as the white-throated rails from Madagascar; they had just evolved a different trait: flightlessness. Because as climate and environmental changes wipe out species, the ones that eventually return will have a different genetic makeup. To recreate an extinct species exactly, evolution would have to reproduce not just its traits but its entire genetic code — an impossibly specific combination. Each species’ genome contains billions of base pairs, and even small mutations (a few hundred or thousand changes) create new biological identities.

With millions of mutations occurring across countless generations, the odds of nature reassembling the same blueprint are effectively zero.

Humans, not as we know them

So, it’s not looking hopeful for Homo sapiens. If every single human were to die tomorrow, the chance of the Homo sapiens genome evolving identically is negligible. The question then becomes, could human-like traits reemerge over billions of years?

The paleontologist Simon Conway Morris points out that there are common and widespread patterns of convergent evolution in life’s history, where similar adaptations, like eyes, wings, and streamlined bodies, evolved independently in unrelated lineages. According to Conway Morris, evolution often follows similar paths because the physical and biological constraints of life funnel it toward optimal solutions. He argues that the emergence of a “self-conscious, intelligent life form” is not an accident but a likely outcome of evolutionary processes.

Conway Morris points to intelligence in other animals — such as crows using tools, dolphins solving problems, and octopuses escaping enclosures — as evidence that cognition has emerged multiple times in different ways. For Conway Morris, human-level intelligence is a convergent trait that might well appear again given the right conditions. Evolution, he argues, is not purely random; it’s shaped by deep structural patterns that lead to recurring outcomes — even complex ones like minds capable of self-awareness.

So, there is some hope for cognition, mindedness, and human-like intelligence. As Ord put it, “Having that kind of safety net — where something might re-evolve after extinction — is definitely something, but it’s a much smaller chance than people imagine.”

How rare we are

The only consolation to this is that it’s highly unlikely that human hands alone — by nuclear weapons, AI, artificial viruses, and so on — could eliminate all life on Earth. And that’s a good thing. As Ord told me: “If all life on Earth were to go extinct, that would be a lot worse…All of the future individuals that could ever live would be lost…It’s taken about four and a half billion years to get to the point that we’re at now, and the Earth probably only has about 500 million more years for complex life before it will be too hot.”

But within that 500 million, the overwhelmingly safe bet is to say that intelligence will evolve if Homo sapiens were to vanish overnight.

When you spend time reflecting on human extinction, it does allow us to appreciate just how unique and lucky we are to be here now. My writing this article and you reading it are the lucky result of winning a million lotteries. As the paleontologist Stephen Jay Gould famously argued, if you “replayed the tape of life,” the outcome would be entirely different. No humans. No Mozart. Maybe just more mollusks.