The place to start looking for evidence here is the morphology of early hominids. In geographic terms this means specifically East Africa, about 2.5 million years ago. Until roughly this date the hominids that inhabited parts of the African continent were probably mostly plant-eaters. The emphasis here should be on the words “probably,” and “mostly.” The reason for this is that when tools show up in the fossil record (that is to say, stones which appear to have been purposefully shaped) we can safely assume that the creatures doing this were using them to get at marrow and strip flesh from bones — in other words, they were after animal protein. Before this technology was developed, eating any meat was more of a challenge.
Scientific consensus for when this happened seems to be around 2.5 million years ago, and this associates it with the being known as Homo Habilis, or “Handyman.” This could have happened earlier, and if so it would have been associated with a slightly different type of hominid (or what some more laid-back scientists allow us to call “ape-men”). Australopithecus, or “southern ape,” shows up in the fossil record about 3.5 million years ago. The best-known example of this creature is of course Lucy, so named for the song “Lucy in the Sky with Diamonds” playing on the anthropologists’ radio when she was discovered in 1974. Lucy was certainly more ape than human, only about 3–4 feet tall, and quite hairy, with a sloping, chinless face and not much of a nose.
For further information on her diet, you’d need to look at Lucy’s teeth. Dental remains allow us to get an idea of her diet. In this case, her dental “microwear” suggested that she was mainly a plant eater, able to manage harder foodstuffs in droughts — bark, stringy plants, etc. Her consumption of animal protein, however, was probably limited to small mammals and insects.
So far, then, from Lucy through Habilis, we (I use the term loosely) were not really “carnivores.” We might have been occasional scavengers, not eating meat in quantities or regularly, and certainly not killing anything big ourselves for the pot. And there were no pots.
But let’s look more closely at Homo Habilis. Her invention of stone tools (we’re not talking about a whole chest of ’em here, just a couple of variations — the “Swiss Army knife of the Paleolithic”) was a game-changer. Previously, hominids like Lucy were kind of vulnerable. Here’s the linguist Dereck Bickerton describing the situation: “It is more than likely that some of our ancestors suffered the ignominious fate of being eaten by weasels. Some of them, it’s pretty certain, were eaten by birds.” They were largely helpless, in other words, and relatively small, in a very dangerous world of large predators.
But Habilis had not discovered weapons — only tools. So how did a rock with a somewhat sharp edge help matters? No, it could not kill a leopard, or hyena. Its benefit was more circuitous, but it looks something like this: The small amount of animal protein gleaned by eating bone marrow and scraps of scavenged meat led to a feedback loop along the following lines: more meat = bigger brains. Bigger brains = more meat.
Taking advantage of meat protein was also a much more efficient way of acquiring energy for those who could get it. Daniel Lieberman of Harvard University, and his colleagues, have determined that full-time vegetarians like the australopithecines would have needed to go through 15 million “chewing cycles” in a lifetime. That is to say they spent almost all day chewing tough things like tubers. This is how gorillas spend their time, deriving enough energy for their large bodies from relatively inefficient foodstuffs. Luckily this works just fine for gorillas, who are able, in their natural environment, to find said foodstuffs (and have enough time in their schedules to chew it). Anyone who has tried a raw diet will attest that it requires that you stay at the table, chewing, long after the cooked-food eaters in the family have moved on.
The energy available from meat — especially pounded, and later cooked — was ounce-for-ounce considerably greater than that of vegetation. As we added meat to the diet, we therefore had time for activities beyond chewing.
While we started out as wholly amateur carnivores, as this line of hominids evolved, nature selected for bigger brains. This was a game changer. The biologist E.O. Wilson considered the evolution of the human brain the most important development in human history, as it allowed for everything downstream of it, most notably the social cooperation that is touted by evolutionary biologists, among others, as being the key human attribute.
This development of bigger brains was never a no-brainer (excuse the pun), however. If it had been, all mammals would be brainiacs by now. As it was, only the hominid line showed extraordinary growth in brain size over the millennia. The payoff was long-term, but it was significant. The downsides were also considerable. The brain is an energy-hungry organ. Accounting for some two percent of our body weight, it consumes about 20 percent of our daily energy. This means it needs extra calories. And the head that is required to store such an organ must be large, causing severe risks for childbirth, especially in a species with the kind of narrow hips that bipedal creatures have. Notwithstanding these risks, nature selected for large brains because individuals with them tended to survive to reproductive age, and this is the only criterion that matters in evolutionary terms.
The Habilis brain averaged 650cc, versus the 3–400cc of earlier australopithecines. Habilis survived for hundreds of thousands of years. But, by 1.8 million years ago, we see a new face on the block. This one is a little more “human” in appearance. Homo Ergaster, or “working man,” was a different species, and recognizably closer to modern humans. As the historian Daniel Lord Smail puts it: “If they chose to have sex in public you would feel shocked or embarrassed rather than giggly.” This creature was about six-foot tall, fully upright, a little less hairy, and they were working the stone tools effectively. They even created a refinement of the bone-basher, a bi-faced hand axe which scientists call the “Acheulian” hand axe (from Acheul in France where early examples were found). They were distributed in a massive area from Africa to Europe and western Asia.
The spread of this tool is relevant because this is the species which many believe first left Africa, our ancestral birthplace, and started colonizing other parts of the globe. Diet continued to be of vital importance to their brain and body function, and meat was central. Ergaster, still feeding on roots, tubers, berries and nuts, was also scavenging meat more widely than its predecessors, and possibly even cooking it, which allowed digestion of tougher materials and the release of more nutrients.
The social consequences of cooking have also recently been shown to have been vital in the making of human social life — the hearth being perhaps the earliest human institution — and cooking itself created pair bond relationships and wider social connections. Apart from the morphological changes — height, facial features, etc. — Ergaster also exhibited social and behavioral changes. Clearly they had undergone evolutionary shifts. “Whatever selection pressures favored these shifts,” say Lieberman et al., “they would not have been possible without increased meat consumption combined with food processing technology.”