Skull and Bones: The Pleistocene Diet
Posted by Richard Conniff on May 28, 2013
Let me admit up front that I am an enthusiastic admirer of predatory behaviors. I have taken unseemly delight in the spectacle of a cheetah tackling and disassembling a wildebeest. And once, while tracking radio-collared African wild dogs in Botswana, I had the great privilege of arriving at the scene of the kill before the rest of the pack. (The smell of fresh blood in the morning. Hmmmm.) When a television documentary dwells mournfully on the plight of an aging zebra no longer able to keep up with the herd, I am generally rooting for the killers.
And I have a hunch I am not alone. Research on predatory behaviors has been in the news a lot lately, starting with the discovery of the earliest known archaeological evidence of our own past as predators, and as scavengers on other predators’ kills. Writing early this month in PLOS ONE, Baylor University anthropologist Joseph Ferraro and his co-authors describe new finds from the Kanjera archaeological site [photo] on the shores of Lake Victoria in western Kenya.
For our hominin ancestors two million years ago, this was the perfect picnic spot, a grassy plain between the shore of a lake and the wooded slopes of nearby hills and mountains. And the menu? Mainly small to mid-size antelopes like Grant’s gazelle and topi, but with the occasional buffalo or hippopotamus as a special treat.
The authors of the new paper note that when modern lions or hyenas kill small antelope, they generally consume the carcass within minutes after death. “As a result, hominins could only have acquired these valuable remains on the savanna through active hunting.” The fossil bones also show evidence of tool use “consistent with both defleshing and disarticulation activities,” including marks of fist-size hammerstones for breaking through to the luscious marrow.
A somewhat macabre feature of the archaeological site is the disproportionate number of animal heads. The likely explanation, according to Ferraro, is that lions and other predators often cannot break open the skulls of their prey to get at the nutritious brain. So our hominin ancestors probably scavenged these leftovers and carried them home to be butchered—the original doggy bag. “These remains,” the authors note, “contain a wealth of fatty, calorie-packed, nutrient-rich tissues: a rare and valuable food resource in a grassland setting where alternate high-value foodstuffs (fruits, nuts, etc.) are often unavailable.”
The new study’s evidence of “persistent carnivory” at a date at least 200,000 years earlier than previously thought is important in understanding our own evolution. Hunting and scavenging for meat caused the hominin gut to evolve from a chimpanzee-like configuration adapted primarily for digesting plant parts, the paper reports, to a more carnivore-like configuration better suited to extracting complex nutrients from meat. The richer menu, says Ferraro, probably also “facilitated brain expansion in human evolution, movement of hominins out of Africa and into Eurasia, as well as important shifts in our social behavior, anatomy and physiology.”
Two other news items this month address some of the darker consequences of our proclivity for meat. The first is a study in the Proceedings of the National Academy of Sciences disputing the theory that, roughly 40,000 years ago, human Big Game hunting of the most reckless sort killed off the spectacular megafauna in the Pleistocene continent of Sahul, consisting of modern Australia, New Guinea, and Tasmania.
The 90 or so giant animal species that originally inhabited this continent were a colorful lot, according to lead author Stephen Wroe of the University of New South Wales. They included “the largest marsupial that ever lived—the rhinoceros-sized Diprotodon—and short-faced kangaroos so big we can’t even be sure they could hop.” Preying on them were goanna lizards “the size of large saltwater crocodiles with toxic saliva,” similar to modern-day Komodo dragons. There were also “bizarre but deadly marsupial lions with flick-blades on their thumbs and bolt cutters for teeth.”
But most of them had disappeared long before humans arrived in the area about 70,000 years ago. And “there has never been any direct evidence of humans preying on extinct megafauna in Sahul, or even of a tool-kit that was appropriate for big-game hunting,” says Wroe. The new paper points the finger instead at natural changes in climate. The authors base their argument on evidence—including ice cores in the Antarctic, ancient lake levels in central Australia, and other environmental indicators—that the megafauna died out as the continent experienced increasingly arid and erratic climate over the past 450,000 years.
The second news item reports on a much different theory to explain the disappearance of another group of megafauna—the mastodons that roamed the forests of North America until they suddenly vanished about 12,000 years ago. Based on physical evidence of conflict on mastodon carcasses, Daniel Fisher of the University of Michigan proposes that humans drove the extinction process not just by hunting, but by inadvertently setting off a mastodon civil war.
Fisher found physical evidence of conflict includes tusk puncture wounds and smashed bones on female mastodons. A normal pachyderm society is highly structured and stable, and females would have been aloof from that sort of combat. But Fisher’s anarchic hypothesis, which he describes in a new BBC documentary Ice Age Giants, also derives from modern experience with elephants. Up until 1995, South Africa regularly engaged in machine-gun culling of excess elephants. Traumatized orphan males, growing up in destabilized societies that lacked dominant bulls, became highly aggressive against other elephants and humans—and at some parks even raped and killed rhinos.
“The normal structure of elephant society,” says Fisher, “is one where the old bulls keep the younger males in check. When the big bulls are pulled out of the picture, all hell breaks loose.” He cites evidence that early human hunters targeted big, dominant male mastodons, leaving inexperienced juveniles to wage war for their spots in the hierarchy.
While Fisher’s finding conflicts with the theories of other researchers that contend mastodons succumbed mainly to the effects of climate change as the Ice Age ended, it is in keeping with our continuing fascination with the kill, even if it’s become only a guilty pleasure vicariously enjoyed by way of a National Geographic documentary.