We can't say that when x happens we get a mass extinction. To the extent we understand mass extinction, one has been caused by glaciation event, one has been caused by a massive climate change, and one has been caused by an asteroid. These events turn out to have no precedent.

Of the many species that have existed on earth - estimates run as high as fifty billion - more than ninety-nine per cent have disappeared. In the light of this, it is sometimes joked that all of life today amounts to little more than a rounding error.

Mitochondrial DNA, which is a sort of abridged version of DNA, is passed directly from mother to child, so it's something that can be looked at to trace matrilineal descent.

If in your lifetime you watch a species go extinct, or plummet almost to the point of extinction, that is a sign that something really serious is going on.

I traveled really to amazing places. I went to the Great Barrier Reef, I went to the Amazon, I went to the Andes, to try to bring people stories of sort of what's going on out in the world and bring this issue alive, in a way, and put it out there.

For a long time, science has gone in the direction of sort of putting people in their place. We learned that the sun doesn't revolve around the Earth, the Earth revolves around the sun; we learned that we're just another species, evolved, like all other species, so we're just another animal, really.

Humans will eventually become extinct. People treat that as a radical thing to say. But the fossil record shows us that everything eventually becomes extinct.