Spicy Ideas From Evolutionary Biology - Dr Jerry Coyne

How do you describe the central thread of your work over the years?

Well, I'm retired now, so the thread has sort of changed direction. But when I was a scientist, I call myself a superannuated scientist now, but when I was working in the lab, I worked on the problem of speciation or the origin of species, which is, of course, the title of Darwin's 1859 book. And it's a problem that Darwin didn't solve, (laughs) so that's why I took it up when I was a graduate student. I think we know a lot more now. We certainly... Darwin knew almost nothing about speciation, so to call his book the Origin of Species is a bit of a misnomer. He should call it the Origin of Adaptations-

Hmm.

... which might be a natural selection. But in terms of species, there is a lumpiness of nature. The fact that creatures are not a spectrum, but they're discrete, more or less discrete. It's, these, that's a problem that Darwin didn't solve, and that's the problem I was working on.

Right. How do you... What's the layman's description of speciation?

Well, are you talking about them, how it happens or what, how I define it?

Give us both.

Well, the definition is simply the... Speciation is the origin of species, and if you look at nature, as I said, you don't find that it's a continuum all the way from bacteria to, you know, humans. It, but that's not a, a hierarchy, that's just what people perceive as a hierarchy. It's lumpy. So if you look at a bird out your window, you're gonna know what it is instantly. You're not gonna say, "I don't know. It looks like a half black bird and a half robin or whatever." No. They come in pretty discrete packages. And that is the problem of speciation. What on earth would make a continuous evolutionary process give rise to entities that are absolutely discontinuous? And that's the, that's really the problem of the origin of species-

Right.

... that Darwin made almost no inroads on it whatsoever.

Why was it a difficult circle to square for him?

Well, because it, in order to attack the problem with speciation, you have to know what species are. And although we say nature is lumpy and these lumps are species, that, that's not really the problem. The question is, well, why do we get those lumps? And it was in about the 1930s that people realized that those lumps are kept separate by what we call reproductive isolated barriers. That is, barriers that keep the genes from one species from mixing with those of another species. For example, those barriers could be, um, that the hybrids are sterile or inviable, so even if they mate, you don't get any intermixing, or they, they couldn't like each other. I mean, w- like a lion and a tiger, they'll mate in the zoo and produce things like ligers or tiglons, uh, which they have, but where they co-occur or where they used to co-occur, in, let's say the Gir forests of India, they don't interbreed. And in nature there's a lot of animals that just simply don't like the way they look, they don't like the, um, mating behavior of the species, they don't like the pheromones of the other species, or in the case of plants, they produce pollen and eggs at different times. That's called temporal isolation. So there's all these barriers that keep members of different species apart. Now that immediately raises the problem that you wanna solve, which is how do these barriers come about to keep species separate in a continuous evolutionary process? So that's what I was working on.