Children are fascinated by dinosaurs. I used to imagine myself transported into the past, my imagination stimulated by Jules Verne’s Journey to the Center of the Earth. In my mind I would roam those ancient landscapes with the giant vegetarian brontosaurus, unharmed by the mighty tyrannosaur. I loved, too, mind-walking in the older world of the giant amphibians, that watery realm of swamps and huge ferns. And sometimes I dreamed of watching woolly mammoths and saber-toothed tigers. But they were gone, and I had no time capsule. And there were no marvels of technology to re-create those creatures of long ago—as did the extraordinary BBC TV series Walking with Dinosaurs.

And then I learned, from one of my books, about the dodo. That extinction was very different from the loss of the dinosaurs. The dodo (and countless others) would still have been around, I discovered, but for modern Homo sapiens. Of course, our Stone Age ancestors had hunted and killed animals. I would later see evidence of this when I worked with Louis Leakey in Olduvai Gorge. But it was hard work for them with only their primitive stone tools. Moreover, the prey animals in Africa had evolved along with the predators that hunted them, and had developed myriad ways to escape being killed. How different when Captain Cook and his sailors killed the unsuspecting flightless dodos, feeling safe on their island with no instinct for flight—and so they were eaten to extinction.

When I was a child, more than seventy years ago, there was no television and no Internet to trap me in front of electronic screens. Instead I spent hours watching birds and insects in our garden, a...