There’s no debating evolution, but a debate remains among biologists over how it actually works. Is evolution deterministic in that its outcomes could not have been otherwise, or is it more random? Harvard biologist Jonathan Losos defends the view that evolution is not deterministic, that takes many different pathways to endpoints that are historically contingent. Take for instance the island of New Zealand which has been geographically isolated from Australia for 80 million years. If evolution were deterministic, we’d expect to see dinosaurs just as they had once existed on Earth, but we see kiwis and moas instead. Losos says that has important implications for life may look like on alien worlds, i.e. don’t expect any spacefaring T. rexes. Learn more about evolution from his book, Improbable Destinies: Fate, Chance, and the Future of Evolution.

JONATHAN LOSOS: So there’s a lot of discussion of what might life look like on other planets, if life has evolved there. Will it diversify in a way like the world today? And there’s a lot of speculation about that question.

But we actually don’t need to go to other planets to ask that question. And that’s because there are different places on Earth that have had different evolutionary histories. And so we can ask on different places in the world, has life evolved in the same way under similar conditions? And it turns out that we’re very well set for that, because there are isolated islands that have been their own evolutionary theaters, if you will, that life has evolved very differently or very independently for a long time.

The best example of that I think is New Zealand. Now New Zealand broke off from Australia about 80 million years ago. And this was before most modern mammal groups had really diversified. And, in fact, today there are no native land mammals on New Zealand. There are some seals that come ashore on the beach, there are a few species of bats, but there are no rodents, there are no carnivores, and so on, except the ones that humans have introduced in the last couple hundred years.

So the question is how did New Zealand evolve in the absence of land mammals? Well it turns out that birds in particular have taken advantage of that and they’ve evolved to do many of the things that mammals do elsewhere in the world. And there are carnivores and herbivores and all kinds of birds.

Now if we thought that evolution is deterministic then we would expect New Zealand, even though it’s dominated by birds, to have species very similar to those elsewhere in the world. But that’s not at all the case. The best example is the kiwi.

Now people know the kiwi, it’s a bird this big. It turns out that it has no wings. It runs around on the ground. It has an extremely good sense of smell, which is very unusual for birds. It also has little whiskers, very similar to mammals. Basically a kiwi does the same thing that a hedgehog or maybe a badger or an armadillo does. It goes around rooting through the leaf litter looking for worms and other invertebrates. Yet it has adapted in a very different way.

And, in fact, the entire cast of characters in New Zealand is very different. There are carnivorous parrots, there are parrots that are completely flightless and walk around on the ground looking for seeds. There was a ten foot tall moa, a land bird that can’t fly, that is the dominant herbivore that looks nothing like a deer or a bison or its ecological equivalence elsewhere.

So New Zealand is an alternative world if you will. Almost an alternative planet in evolutionary terms. What has evolved there is completely different from the rest of the world. And this is true of other places. Australia in at least some respects is very different. Madagascar – or go back to the age of the dinosaurs. Well the dinosaurs came, they went extinct. If evolution is so deterministic why don’t we have t-rex and brontosaurus-type dinosaurs today? It’s because evolution has gone in a very different direction.

So we don’t need to go to other planets to see how deterministic evolution is. We can just look in different places on Earth and we can see that the outcome often is very different.