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A biologist explores a big question in evolution: does it happen the same way each time?

Replaying the tape of life

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The scientist and writer Stephen Jay Gould famously claimed that if you “replay the tape of life” and started all over again, the end result would be very different. In other words, he argued that evolution wasn’t preprogrammed; rather, it depended on the environment and circumstances.

As a child, Jonathan Losos was swayed by this argument. But as an adult and evolutionary biologist, his own research seemed to argue against the claim that evolution is wholly contingent. In Improbable Destinies: Fate, Chance, and the Future of Evolution, Losos decided to explore the question of the extent to which evolutionary fate is predetermined versus whether it’s a quirky outcome of particular circumstances.

The Verge spoke to Losos about competing theories of evolution, experimental studies on evolution, and what all this means for aliens.

This interview has been lightly edited and condensed for clarity.

What made you want to write this book? Tell me about how your own research informed this decision.

I’m an evolutionary biologist, and I’ve spent my career studying the evolution of lizards, in particular. It turns out that lizards are a really good group to study evolutionary theories: they’ve been around for a long time, they’re diverse, and studied in many different ways. The particular lizards I study, called anoles, are found on islands in the Caribbean, and they exhibit a very unusual pattern. They have evolved independently on the four big islands and produced more or less the same set of traits, and that’s a pretty unusual phenomenon.

Jonathan Losos.
Photo: Riverhead Books

So Gould was very persuasive, and he’s a brilliant writer. But in some respect, my lizards were evolutionary replays. We weren’t going back in time, but starting with different islands and seeing what happened seemed to be counter to what Gould had argued. I was pretty much on his side and viewed my research as the rare exception that proves the rule. I have to say, it caused a little bit of internal conflict because other people started citing my work as opposing Gould, and that put me in a bit of cognitive dissonance.

Before we get to discussing who is ultimately right, can you tell me about some of the research that supports Gould?

My favorite example of supporting Gould is the duck-billed platypus. A lot of people make fun of the duck-billed platypus, saying it’s a ridiculous mishmash of parts and can only exist in parts of Australia and not anywhere else. But, actually, it’s marvelously adapted for its life! Its bill can detect electrical currents in the water, and so it can detect a crayfish moving its muscles since that puts out a little electrical discharge.

So they’re well-adapted to the streams of eastern Australia, but they occupy a habitat that is found all around the world. We have them in North America, in the background where I grew up in St Louis. If evolution is so predictable, if exposure to a particular environment should lead to adaptation in the same way time and time again, then we should have duck-billed platypuses everywhere. And there’s my favorite example. But there are long lists of animals very well-adapted to their way of life that have no parallel. So I think this supports Gould’s idea that the quirks of history lead evolution in one way or the other.

But what about the opposing evidence?

On the other hand, there are also many examples of distantly related species that evolved the same adaptations, seemingly supporting the idea that natural selection favors the same outcome time and time again. If you look at the top fast-swimming marine predators in the world — compare, say, a shark and a dolphin — they look very much the same. There is an optimal way to move quickly through the water, which involves having a streamlined body with propulsions coming from your back end, and that’s why dolphins and sharks and marine reptiles have evolved to be very similar. There certainly are some cases in which natural selection is so strong and favors a single outcome that you get the same result.

One of the most interesting parts of your book is that you discuss the experimental biology techniques being used to study this. Can you tell us about them?

Experimental biology is an exciting area where people are doing experiments in the lab on fast-evolving organisms where they can study evolution in real time. There was one fantastic study that began 30 years ago where the scientist Rich Lenski at Michigan State set up a Petri dish of E. coli in an environment that it wasn’t well-adapted to. He set up 12 dishes, each with a clone of the same E. coli, and he let them evolve independently. It’s gone on for 30 years now, for 70,000 E. coli generations, and it’s allowed us to test this idea of those populations in the same situation and see if they adapt in the same way.

And the results have been fascinating. They’ve shown that, for the most part, the populations do adapt in the same way. They get better at eating the resources, and when you look at how they’re doing it, they do it in much the same way, and there’s a lot of repeatability from one instance to the next.

However, they’ve also shown that occasionally they do something very different. In the case of this E. coli experiment, one of the populations evolved a completely different adaptation that lets it attain population density 10 times as high as any of the others. So this clearly shows that even though oftentimes evolution will occur in the same way given the same circumstances, occasionally it does something extremely different.

What’s the largest or most complex animal that scientists have done these experiments on?

Fruit flies are probably the largest organism. But I would say the other exciting thing about this work is that it’s not just going on in the lab. People are now taking the same approach in nature. We used to think evolution occurred much too slowly to do out in the real world, but we now know that’s not true. When natural selection is strong, evolution can occur very rapidly. There’s a great study on mice in Nebraska that’s wrapping up. They put mice on different-colored soils to see if they would evolve to match their soil’s color, and they did.

Do we have insight into why sometimes they evolve more similarly or differently? Do we know the “rules” yet?

It’s too early to know, but one generality that does seem to be emerging, and it’s one that makes sense, is that closely related species tend to evolve the same way. Whereas if you expose distantly related species in the same circumstances, they often find different ways to adapt.

That makes sense because closely related species often have the same variation in genes and can take a more similar route to adapt. If you look at closely related species like different populations of E. coli or the same species of mouse, they often find the same adaptation. Distantly related species are very genetically different, and they often have somewhat different lifestyles that may make it more easy to adapt one way or another.

In the last part of your book, you talk about aliens a bit, and I wanted to ask about this. What does this mean for how we imagine alien life?

Science fiction is full of movies and books about life on other planets and how similar it would be. Certainly, if you believe Hollywood, every depiction is that intelligent life on other planets is very similar to humans: a two-legged species with a big head and probably two arms, basically humanoid organisms. I think that is very unlikely.

The more different species are, the more likely they are to evolve in different ways and adapt in different ways, and certainly, life on another planet couldn’t be more dissimilar to life here. Different genetic systems... who knows how natural selection operates, who knows what life will be based on? There are well-respected scientists who predict that life will be extremely similar and be humanoid, and they base that on the idea of convergent evolution, but I disagree. I think life will be so different that it will find different ways to adapt, even on an Earth-like planet.