A year ago I blogged about Richard Wrangham’s book, Catching Fire: How Cooking Made Us Human (it’s a great book, and I recommend it). My main interest in the post was, what were the implications for the diet of our ancestors? And what are they for those of us who follow the Paleo Diet?
As I recollect it (I don’t have the book in Toulouse, where I am currently visiting), Richard’s argument is that our Australopithecine ancestors fueled their relatively small brains, 450 cubic cm (compared with 350-400 cubic cm for forest apes) by digging up underground storage organs of plants, which are rich in starches.
The first members of genus Homo, such as Homo habilis, probably fueled their larger brains, 600 cubic cm, by shifting to eating meat, marrow, and brains of animals they scavenged. Then the big change came – Homo erectus with 870 cubic cm and Homo sapiens (that’s us) with 1400 cubic cm. Richard Wrangham thinks that this jump in cranial capacity was literally fueled by fire, or rather by the ability to cook. Cooking made large guts unnecessary and allowed efficient extraction of energy from food. Let’s call this the Wrangham scenario.
Last week I was discussing this idea by e-mail with Loren Cordain, a Paleo diet pioneer (see his book Paleo Diet). Loren makes an interesting point about how we can estimate when human beings learned to make fire.
The main way that people made fire in prehistory was by using wood on wood friction.
As an aside, in medieval times the main method switched to striking flint with steel, but that required having access to iron, which became widely available very recently, as far as human evolutionary history goes.
Of course, “friction” doesn’t mean that you just rub two pieces of wood together. Instead, you use a fire drill (see Loren’s blog post about it).
The discovery of this method was clearly a side effect of drilling holes to produce, for example, beads for necklaces. It’s an interested case of cumulative culture. You first need to develop a technology for drilling holes in objects. Then, one day as you are drilling a hole in a wooden bead, it suddenly goes up in flames. It’s hard to imagine how a fire drill could be invented any other way.
Items with drilled holes appear relatively late. Thus, according to Loren’s argument, the discovery of the fire drill and ability to produce fire at will must be dated to between 100,000 and 75,000 years ago.
The implications that he draws from this conclusion is that fire became important only quite late in our evolutionary history. Since tubers and roots need to be cooked for safe consumption, these starchy foods also must be a relative evolutionary innovation, and should not be part of the Paleo diet.
This is an interesting argument (let’s call it the Cordain scenario), but I am not convinced by it. If the increase of human brain was not driven by plentiful calories obtained from cooked underground storage organs, then where did the energy come from? It must have been bone marrow and brains of scavenged animals. But did early members of the genus Homo have access to dependable and plentiful supply of such foods?
I still prefer the Wrangham alternative. And to me the question of when human beings learned to reliably produce fire is an interesting, but side issue. Learning how to maintain fire and move it around (e.g., in special fire containers) is much more straightforward, and can be perfected in small steps. If one family’s fire is extinguished they can obtain it from others. So human beings could have been using fire for many hundreds of thousands of years before they learned how to make it.
Unfortunately for the Wrangham hypothesis, there is no evidence that fire was used by people before 800,000 years ago, and widespread use of fire is documented starting 300-400 thousand years ago. This is clearly a problem. But any alternative to the Wrangham hypothesis would have to come up with an explanation of where the calories came from and, even more importantly, how early humans could afford to shrink their guts. If you want to thrive on raw vegetarian diet, then you want to look like this: