Janzen wrote to Paul Martin, a Pleistocene ecologist, to ask for a list of extinct American mammals, and together they began working out hypothetical ecological relationships between extinct animals and the anachronistic fruits they’d left behind. Janzen argued that giant animals might have cracked the Cassia grandis pods without any difficulty, passed the seeds through their guts, and deposited them far from the parent tree. He called his theory the “megafaunal dispersal syndrome.”
It’s a persuasive theory. The mamey, a large pink-fleshed tropical fruit (it tastes like marzipan and makes a good ice cream flavor), has an ebony seed so tough that you can’t crack it without a hammer. It will germinate readily, however, if the outer coat is scored, as it might once have been scored by the teeth of a giant animal. There were plenty of animals living in the Americas 100,000 years ago that would have been large enough to swallow a mamey seed. The giant sloths stood about 18 feet tall and weighed more than an African elephant; there were various kinds of mastodons; there was a 3,300 pound rhinoceros-like creature called Toxodon; there were giant armadillos, giant camels, American horses. The list goes on. It would have been a very different world, a frightening world, a world of monsters.
It would also have been a world in which meat was fantastically abundant, which was ultimately unfortunate for the meat, monstrous though it was. Large body size is no doubt a good defense against most predators, but it’s no defense at all against us, since we can kill at a distance. In the beginning, our hunting techniques must have improved only gradually, and that’s why Africa has retained some of its large animals. Evolution was able to keep pace; they learned to fear us. This was not possible for animals in the rest of the world, which encountered humans who had already perfected their hunting techniques. North America lost 32 of its 47 mammalian genera; South America lost 47 of 59; Australia lost all but one of its large mammals (the kangaroo); many islands lost every big mammal and most large birds. And of course we’re now killing the cautious African megafauna as well. It is terrifying to consider: We have no fangs or claws, but we have our big brains, and we are unquestionably the most dangerous thing on earth. And not only that, but we are capable of lamenting this fact.