Monday, May 27, 2013

More Evidence we Evolved on a Meat-Rich Diet

I'm getting the sense that human ancestors were serious meat eaters.

I'm reading The Wisdom of the Bones by Alan Walker and Pat Shipman, a contemporaries and colleagues of Richard Leakey. They discuss evidence that humans moved up in the food chain: increased sociality, territorial expansion and decreased population density, and smaller GI tracts.

Sociality

As Leakey noted in one of his books, if you live on raw vegetation, you can just grab a leaf or a piece of fruit and eat it. You don't need a tribe to do so; in fact, you might want to hide your booty from everyone else so they don't bug you to share it. Hunting big game, on the other hand, requires cooperation. Richard Wrangham says in Catching Fire that some hunter-gatherers have strict rules about women sharing their vegetables only with immediate family members, while men are supposed to share their meat (hunted cooperatively) with the group (Catching Fire, page 163-164). He who eats alone is an orangutan, not a wolf or a lion.

Strong ties between humans go back over a million years to our Homo erectus and Homo egaster ancestors. In Georgia's Caucuses Mountains 1.75 million years ago,

On individual had lost all but one of his teeth long before his death, for layers of bone fill his teeth sockets. He could only have consumed soft food that could be swallowed without chewing, so other members of the band must have looked after him. (Cro-Magnon by Brian Fagan, page 34)

Walker, Leakey and their team unearthed the fossil of a diseased Homo erectus they called 1808. 1808 was an adult female who likely died of hypervitaminosis A from eating the liver of a carnivore--and yet

she must have survived her poisoning for weeks or maybe months while those clots ossified. How else could her blood clots have been so ubiquitous; how else could they have turned to the thick coating of pathological bone that started us on this quest?

The implication stared me in the face: someone else took care of her. Alone, unable to move, delirious, in pain, 1808 wouldn't have lasted two days in the African bush, much less the length of time her skeleton told us she had lived. Someone else brought her water and probably food; unless 1808 lay terribly close to a water source, that meant her helper had some kind of receptacle to carry water in. And someone else protected her from hyenas, lions and jackals on the prowl for a tasty morsel that could not run away. Someone else, I couldn't help thinking, sat with her through long, dark African nights for no good reason except human concern....Her bones are  poignant testimony to the beginnings of sociality, of strong ties among individuals that came to exceed the bonding and friendship we see among baboons or chimps or other nonhuman primates. (The Wisdom of the Bones, page 165, emphasis in original)

Territorial Expansion

Predators necessarily have to be thinner on the ground than their prey. Around 1.8 million years ago, Homo erectus started expanding its territory:

The speed of the territorial expansion of Homo erectus is impressive, especially since geography, climate, fauna and flora would be changing all along the way. It is the sort of expansion that predators undertake successfully...in fact, prey animals rarely expand their territories so far or so fast without evolving into a new species. (The Wisdom of the Bones, page 240)

Australopitchecus fossils have been found mostly in eastern and southern Africa; Homo erectus, throughout much of Africa and as far as Java and northern Europe.

Technology

Walker and Shipman expected to find improved means of slicing up meat. They don't see any real improvement in cutting or hunting tools around that time (1.4 to 1.8 million years ago), but Richard Wrangham (Catching Fire) sees in the fossil record, decreased tooth size and increased brain size from Homo habilis to Homo erectus and other evidence, that our ancestors may have started cooking around two million years ago.

Gut Size

A vegan meme is that humans' longer gut shows that we're natural herbivores. Longer than what? Not longer than our ancestors the Australopithecines like Lucy. Nariokatome boy, an almost-complete Homo erectus skeleton, was long and lean; Lucy was short and pot-bellied:

Lucy
From left: Turkana Boy (Nariokotome boy, a Homo erectus), Lucy (Australopithecus), Neanderthal. Photo from Smithsonian.org.


Walker and Shipman write,

After studying the anatomy, curvature and declination of [Nariokotome boy's] ribs, we concluded that his rib cage was indistinguishable from that of a modern human in almost every respect. It was entirely unlike the rib cage of a chimpanzee or gorilla (or Lucy). Like us, his thorax was barrel-shaped; like us, he must have had a well-defined waist between his narrow hips and his lowest set of ribs....This meant that he could not have the extensive large intestine that herbivores need in order to process their food; there was no room for it in his torso....It was just a question of gut size, and the boy's guts were small. Only predators can afford to have short gastrointestinal tracts, because animal foods are readily broken down, whereas the cellulose walls of vegetable foods have to be cracked open by cellulose-eating bacteria in the fermentation chambers of the gut before the herbivore can benefit from any nutrients. (The Wisdom of the Bones, p. 245)


*****

It's nice to get out of the echo chamber of paleo and low-carb books and blogs and get independent confirmation that humans evolved on a meat-rich diet. How much meat is hard to say; modern hunter-gatherers live in a different climate than that of the ice ages and some live in isolation. (I'm thinking natural selection for the Kitavans: humans who couldn't live on a high-carb diet were winnowed out.) If people wish to eat a high-carb diet (or any other diet), and enjoy good health on it, that's fine, but I'd like to see an end to the idea of high-carb paleo, which appears to be a myth.

4 comments:

Lowcarb team member said...

Interesting article Lori but I was sold, so to speak, on this statement "human ancestors were serious meat eaters."

Now years and years and years and years etc etc later. For me meat, fish, vegetables, low carb fruits, good fats are what I eat, but I can only speak personally, it still has to be each to their own. But we owe it to ourselves to do our research, there is plenty of it.

All the best Jan


tess said...

everyone who touts the "Kitavan high-carb diet" conveniently fails to mention the once-a-day eating pattern. yeah, even i could probably stand a high-carb diet if i ate before bed, stored it as fat, woke up burning fat and kept that up till evening, again. ...but who'd want to?

Lori Miller said...

Jan, I definitely agree with fine-tuning your own diet. A paleo template is a good place to start, and I wish evolutionary history were required in medical school. A gastroenterologist might say, for instance, that if you're eating a high-carb diet and have gastric problems, your non-evolutionary diet might be a problem, rather than sitting there with his finger up his nose.

Lori Miller said...

Tess, the Kitavans smoke like chimneys, too, which helps control their weight. So do the French and Japanese (who also have a lot more cultural bugaboos than Americans do about how and what they eat).

My stomach would be very unhappy on one big, carby meal a day.