Every time we slice into a steak or cut into some chicken, we’re taking part in a technological heritage that stretches back at least 3.4 million years. Back then, the only cutting implements around were sharp pieces of stone and there were no true humans around to wield them. But there were still butchers– one of our ancestral species, Australopithecus afarensis, was already using stone tools to flay meat off bones, leaving small nicks with every cut. Such marked bones have been found and they push back the earliest estimates of tool use among human ancestors by 800,000 years.
In January 2009, a team led by Shannon McPherron from the Max Planck Institute found bones which had clearly been worked over with stone tools. The bones, uncovered in Dikika, Ethiopia, include the rib of a cow-sized animal and the thighbone of a goat-sized one. Both bore cuts and scratches inflicted by sharp objects and dents produced by crushing hammers.
By peering at the marks under powerful microscopes and analysing their chemical composition, McPherron confirmed that they were made by stone rather than teeth, and they were created before the bones fossilised. These were not accidental scratches, but the remnants of strikes used to carve off the meat and break into the marrow.
Many men think of little else besides sex and meat, but male chimpanzees will sometimes exchange one for the other. Chimps are mostly vegetarian but they will occasionally supplement their diet by hunting other animals, especially monkeys. Males do most of the hunting, but they don’t eat their spoils alone – often, they will share the fresh meat with females, even those who are unrelated to them. Some scientists have suggested that this apparently selfless act is a trade – the males are giving up their nutritious catch in exchange for sex.
Cristina Gomes and Christophe Boesch from the Max Planck Institute for Evolutionary Anthropology have found new evidence to support this idea. They spent four years in the Tai National Park in Cote d’Ivoire watching a group of 49 chimps, including 5 adult males and 14 females. They recorded a huge amount of data on the group’s behaviour, and across 3,000 hours of observation, they were privy to 262 bouts of chimp sex.
These years of voyeurism told them that meat was a big factor in separating the Casanovas from the sexually frustrated males. Females mated more frequently with males who gave them meat at least once, and meat-sharing was much more important than other shows of support such as grooming, sharing other types of food or taking their sides in fights. None of these other actions had much bearing on the male’s sexual success.
Gomes and Boesch wonder if human hunter-gatherers rely on similar trades. That’s certainly been suggested before, especially since better hunters tend to have more wives (or at least, more affairs). These results do nothing to confirm or deny that idea, but they certainly provide strong evidence that chimps, at least, are indeed exchanging meat for sex.