The Rational Optimist_ How Prosperity Evolves - Matt Ridley [32]
They were very good at wiping out not only their distant cousins, but also much of their prey, something previous hominid species had not managed. The earliest of the great cave painters, working at Chauvet in southern France 32,000 years ago, was almost obsessed with rhinoceroses. A more recent artist, working at Lascaux 15,000 years later, depicted mostly bisons, bulls and horses – rhinoceroses were rare or extinct in Europe by then. At first, modern human beings around the Mediterranean relied mostly on large mammals for meat. They ate small game only if it was slow-moving – tortoises and limpets were popular. Then, gradually and inexorably, starting in the Middle East, they switched their attention to smaller animals, and especially to fast-breeding species, such as rabbits, hares, partridges and smaller gazelles. They gradually stopped eating tortoises. The archaeological record tells this same story at sites in Israel, Turkey and Italy.
The reason for this shift, say Mary Stiner and Steven Kuhn, was that human population densities were growing too high for the slower-reproducing prey such as tortoises, horses and elephants. Only the fast-breeding rabbits, hares and partridges, and for a while gazelles and deer, could cope with such hunting pressure. This trend accelerated about 15,000 years ago as large game and tortoises disappeared from the Mediterranean diet altogether – driven to the brink of extinction by human predation. (A modern parallel: in the Mojave Desert of California, ravens occasionally kill tortoises for food. But only when landfills provided the ravens with ample alternative food and boosted – subsidised – their numbers did the tortoise numbers start to collapse from raven predation. So modern people, subsidised by hare meat, could extinguish mammoths.)
It is rare for a predator to wipe out its prey altogether. In times of prey scarcity, erectus hominids, like other predators, had simply suffered local depopulation; that in turn would have saved the prey from extinction and the hominid numbers could recover in time. But these new people could innovate their way out of trouble; they could shift their niche, so they continued to thrive even as they extinguished their old prey. The last mammoth to be eaten on the Asian plain was probably thought a rare delicacy, a nice change from hare and gazelle stew. As they adjusted their tactics to catch smaller and faster prey, so the moderns developed better weapons, which in turn enabled them to survive at high densities, though at the expense of extinguishing more of the larger and slower-breeding prey. This pattern of shifting from big prey to small as the former were wiped out was characteristic of the new ex-Africans wherever they went. In Australia, almost all larger animal species, from diprotodons to giant kangaroos, became extinct soon after human beings arrived. In the Americas, human arrival coincided with a sudden extinction of the largest, slowest-breeding beasts. Much later in Madagascar and New Zealand mass extinctions of large animals also followed with human colonisation. (Incidentally, given the obsession of ‘show-off’ male hunters with catching the largest beasts with which to buy prestige in the tribe, it is worth reflecting that these mass extinctions owe something to sexual selection.)
Shall we trade?
Meanwhile, the stream of new technologies