美国国家公共电台 NPR Biologist Jonathan Losos Explores 'Convergent Evolution' In 'Improbable Destinies'（在线收听）

ROBERT SIEGEL, HOST:

Biologist Jonathan Losos and I have at least one thing in common - we were both blown away by the late paleontologist Stephen Jay Gould's 1989 book "Wonderful Life." Gould saw evolution as being all about odd contingencies, accidents. Had one evolutionary step gone a different way, life on Earth could've ended up radically different. Losos read the book, and Gould helped inspire him to become a biologist. He's a professor at Harvard and the author of a new book called "Improbable Destinies." One thing he is not anymore is quite so much a believer in Gould's insistence on chance and contingency driving evolutionary change. Jonathan Losos, welcome to the program.

JONATHAN LOSOS: Thank you very much; a pleasure to be here.

SIEGEL: At the heart of your book and your conversion, I guess, is the growth in recent decades of an understanding of convergence as a principle in evolution. Can you define convergence for us?

LOSOS: Well, convergent evolution is when two species independently evolve to be similar.

SIEGEL: And the best example that you give that I can recall is the remains of an aquatic dinosaur, a dolphin and a shark. They all developed dorsal fins, flippers, sleek bodies, but they didn't all develop from the same set of accidents that were happening randomly.

LOSOS: That's absolutely true. They evolved from three very different ancestors, and yet they ended up looking almost identical. They're all streamlined animals with a powerful tail for propulsion, two flippers for steering and a dorsal fin for stability. So the animals, if you saw one, you might - people mistake sharks for dolphins and the other way around. And so they have convergently evolved to be very similar. Now, the reason they've done that is that they have evolved a body form that is very optimally designed for moving quickly through water. And so in fact, if engineers were designing an animal to do that, that's pretty much the body shape they would pick.

SIEGEL: So the idea of convergent evolution is that common environmental factors would drive evolutionary change in some common directions. It's not all haphazard and accidental in that sense.

LOSOS: Yes, exactly. Convergent evolution most commonly occurs when species adapt to the same environmental circumstance in the same way.

SIEGEL: Has genomic research been the difference here? I mean, we've known for a long time that a shark and a dolphin are different. But is it that we can now see how unrelated an English finch and a very similar Australian finch are in a way that we couldn't see before?

LOSOS: That's exactly it. We've known about convergent evolution for a very long time. Charles Darwin remarked upon it in "On The Origin Of Species." But we had no idea how common it was. And that was until we've gotten a better idea of the evolutionary tree of life, of how species are related to each other. And the flood of molecular DNA data that has come forth in the last two decades or so has in many cases revised our understanding about how species are related to each other. And it has revealed that many species that we thought were similar because they're closely related, that they're not closely related and that their similarity is the result of convergent evolution.

SIEGEL: Of course, one interesting speculative debate is the question of whether life on other planets would resemble life on Earth. And accepting the power of convergence as a guiding principle, I guess the answer would probably be yes. There are structural and environmental reasons for life developing as it has here. I mean, they would probably apply elsewhere.

LOSOS: We now know in just the last few years that there are many, many planets in the universe very similar to Earth - millions, maybe billions, in our own Milky Way galaxy. And so many scientists think that if there are that many Earth-like planets - and what I mean by Earth-like is of similar size, chemical composition, running water, temperature and so on, so very similar in many respects to Earth. Many scientists believe if that's the case, that life perhaps inevitably has evolved on some of them. And so the argument goes that if the environment is similar on those planets, then life would have evolved and adapted in the same ways. Some go so far to say even that beings very much like us, humanoidlike beings, would've evolved on those planets.

SIEGEL: You write about the three-spined stickleback fish. What wisdom do we gain from this species?

LOSOS: Well, the three-spined stickleback is another case of evolutionary convergence. In lakes in British Columbia, they have diverged into two types - one that lives on the bottom of a lake foraging in the mud in the bottom, the other in the open water catching little invertebrates. But what has happened is on six different lakes they have evolved into these two types that are indistinguishable from one lake to another. And in fact, on the University of British Columbia campus, they have developed an enormous complex of artificial ponds in which they have seeded them with sticklebacks to watch how they evolve over many generations.

SIEGEL: And when they sort out into open-water sticklebacks and bottom-feeding sticklebacks, at some point they become non-interbreeding different species of three-finned sticklebacks?

LOSOS: Well, the really interesting thing here is that, yes, in any one of those lakes, they adapt to the two different habitats. And eventually they become so that they don't interbreed with each other. However, if you put together the same type of fish from different lakes, even though they've independently adapted to those niches, they will interbreed with each other.

SIEGEL: That's amazing. So in effect, biologists at the University of British Columbia are creating evolution.

LOSOS: Yes. Yes. That's exactly it. To my mind, this is the most exciting advance in evolutionary biology - perhaps one of the most exciting advances in all of science - in the last few years, the realization that evolutionary change can occur not only very rapidly, but so rapidly that you can actually do experiments and expect to see an outcome in three to four years. This is something that Darwin got completely wrong.

I mean, Darwin was right about so many things. It is amazing. But he was completely wrong on the pace of evolution. He thought that evolution occurred so glacially slowly that it would take thousands of years to be able to detect it at all. Well, now that we know that evolution can occur very quickly, we can actually go out and do experiments in nature to test our ideas. And some of the experiments going on now are just extraordinary and providing incredible insight about the evolutionary process.

SIEGEL: Well, Jonathan Losos, thank you very much for talking with us about it and about your book.

LOSOS: Well, it's been my pleasure.

SIEGEL: Professor Losos' book is called "Improbable Destinies: Fate, Chance, And The Future Of Evolution."