Sunday, August 02, 2009

Its the fire, stupid

What made us human? This is a hard question (unless all of your answers end with "because God did it"). Bipedalism, acquisition of language, opposable thumbs (plus tool building), etc. have all been proposed as possible explanations for an increase in cognitive abilities of humans compared to those of the apes. Now there are two new books that argue that the ability to control fire my have been the key factor. From Science (Jul 24):
Two new books by anthropologists Frances Burton and Richard Wrangham, released within weeks of each other, now argue that learning to control fire a few million years ago "made us human" or "ignited human evolution." Each comes in a black dust-jacket with the title and author's name written in white and yellow above the picture of a campfire. Each draws on evidence from anthropology, archaeology, and comparative primatology to provide a fascinating account of how fire was first used and controlled. However, the similarities end there.

In Fire: The Spark That Ignited Human Evolution, Burton (University of Toronto) argues that the light from campfires extended the day for our ancestors and therefore decreased their melatonin levels. She discusses the effects of melatonin on cognitive abilities, reproduction, and other physiological processes, but she does not directly connect the light from a campfire to accelerated genetic changes. At the conclusion of her account, she describes the ultimate effect of light as "accelerating processes of mind, body, disease, and society in the transformation to us." Wrangham (Harvard University) presents evidence that it's the heat and not the light of fire that was important. Catching Fire: How Cooking Made Us Human offers a convincing argument that cooking allowed us to do the work of chewing and digesting outside of our bodies.

Wrangham presents evidence (sometimes strong and always interesting) that the energy our bodies saved by outsourcing digestion was redirected toward our brains. For example, he discusses the rapid evolution of the beaks in Galapagos finches in response to dietary changes, a self-experiment in which he determines that adding leaves to raw goat meat makes it easier for him to chew, and the food preferences of the gorilla Koko. (She likes her vegetables cooked.)
If Wrangham's arguments convince you that cooking increases caloric content, then it is easy to see that selection would favor anatomical and physiological adaptations to the new foods we created. Cooking would free more energy for the brain, which could then increase in size and advance culture. And so on through the positive feedback loop.
These are interesting ideas. But more importantly, they both generate testable hypotheses:
Both books lead to testable hypotheses. Burton calls the question of whether a campfire produces enough light to affect melatonin levels the "crux" of her book. This suggests an experiment in which melatonin is assayed in subjects in a controlled environment with or without a campfire artificially prolonging the day. Wrangham, surprisingly, could not find a single study that compares human participants on controlled diets of food that is either eaten raw or cooked. Such experiments together with the evidence and the innovative ideas Burton and Wrangham present would help us better understand what made us who we are today.
Here are links to Fire: The spark that ignited human evolution and Catching fire: How cooking made us human. I should really cook more often.


Don said...

Your mention of digestive outsourcing coupled with your stinger of "I should cook more often" made me think of this essay by Michael Pollan. Love him or hate him, the essay is interesting and, like Jeff Lebowski's rug, ties the room together.

Salman Hameed said...

Good point. But of course, if you bring in Lebowski to the discussion, then we will have to go one step further to include the new film, Julie and Julia, to tie evolution, cooking, and pop-culture all together.

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