Catching Fire: How Cooking Made Us Human, by Richard Wrangham (2009)  is the most interesting non-fiction, science related book I’ve read since Guns, Germs and Steel, by Jared Diamond many years ago.  That’s not to say I haven’t read other interesting books in the mean time, just that in the novelty of the claims made, the evidence assembled to back them up and the persuasive chain of reasoning, it interesting at the level of Diamond’s ground-breaking book.

The core argument is that cooking food (also, softening it, or reducing the size of the basic bits — milling) lets the gut extract more energy than if it isn’t cooked.  On the long road to Homo Sapiens, that branch of australopithecus which discovered how to process their food, about 2 million years ago, instead of eating it in-situ, as our other primate ancestors do,  began a process that eventually created our Homo sapiens species.

With less overhead needed in the gut to extract the same amount of energy,   energy was extracted faster and th gut decreased in size; extra energy was available to grow the brain; tooth and  jaw size reduced no longer needed to masticate leaves and tubers for hours every day [chimpanzees spend 6 hours or more a day chewing]; co-operation to protect collected food and the cooks (cooking was visible and took time while the cook was immobilized) began; husband-wife teams began or were solidified; the division of labor into women as plant gatherers and cooks, men as protein hunters, began.  Procreation, depending on female fertility, which depended on stable caloric intake, increased.  Cooking meant that more food was useable and more environments could sustain hominid lives.   Not only that, the implied control of fire meant that warmth was available at night so that body hair could shed, and hominids could roam and run, unhampered by the overheating of their hairy cousins. They no longer needed to climb trees to sleep in safety, as fire protected them.

It is a fascinating argument, drawing much on anthropologists, paleoanthropologists, primatologists, knowledge of skeletal size and posture, digestive physics and chemistry and wide ranging knowledge of the latest, and competing claims in many of these fields.  While not a full fledged scientific theory, it is certainly a sturdy and well conceived hypothesis — as Wrangham himself calls it:  The Cooking Hypothesis:

Humans are adapted to eating cooked food in the same essential way that cows are adapted to eating grass, or fleas to sucking blood, or any other animal to its signature diet.

Many of the links in the chain of argument are buried in the deep past and will likely never be known from empirical data. Evidence of fire, for example, only goes back 100,000 years with debatable evidence at 400,000.  How can the argument be made that cooking began about 2 million years ago –1.6 million years before any evidence of fire?

Tooth size!

As has been seen in present times, the presence or absence of certain types of food leads to swift changes in finch beaks.  They grow larger over generations to deal with hard seeds and nuts.  Smaller beaks will do when softer fruit and berries are plentiful.  How does this fit with differing anatomies in our pre human ancestors?

“…there have been only three periods when our ancestors’ evolution was fast and strong enough to justify changes in the species name.  They are the times that produced Homo erectus (1.8 mya), Homo heidelbergensis (800,000 ya) and Homo Sapiens (200,000 ya)…

…the surface areas of three representative chewing teeth decreased by 21% from habilines to Homo erectus…the largest reduction of tooth size in the last 6 million years of human evolution, the largest increase in body size, and a disappearance of the shoulder, arm and trunk adaptations that apparently allowed habilines to climb well (like chimps do now).  Additionally, Homo erectus had a less flared rib cage and a narrower pelvis than the australopithecines indicating they had a smaller gut.  There was a 42% increase in cranial capacity.

Cooking would have also allowed survival in a wider range of habitats than those for which teeth and gut were specialized.  As today, chimpanzees have a wider range than gorillas because, despite similarities in diet, chimpanzees must have fruits, while gorillas can subsist on leaves and nuts alone.  When berries decrease in an environment, gorillas make do without; chimps must forage wider to find them — which in turn in linked to their smaller size and ability to sustain such extended travelling.  Cooking meant that Homo erectus could range wider, making use of otherwise inedible, or edible but not sufficient foods.  And, it was Homo erectus that was the first habiline to leave Africa, migrating as far as western Asia, Indonesia and western Europe.

Other links in the argument, particularly interesting in these times of changing social roles, have to do with the primacy of women as the cooking half of the team, the role in pair bonding that cooking has in many hunter-gatherer tribes — where the mere offering of cooked food by an unmarried woman is tantamount to a betrothal.  Table manners have long histories of politeness behavior in the same people:  to eat with others, one must patiently wait in invitation, anything else is considered hostile behavior.

Merely the act of sitting around the fire would have begun to select for those who were more tolerant, with less explosive tempers — much as wolves self selected into dogs, the less aggressive being allowed to hang out at the edges of camps, and forage for scraps, while the others were driven off.

Though a bit jarring in the context of the rest of the book, the last chapter shows how the current rise in obesity in the US,and following closely in the rest of the world, is explained by the same evidence.  The more processed food is — the finer the milling of flower– the more calories can be extracted by the gut.  Combinations of foods can increase or decrease this ratio.  The pleasure we get in eating is not un-related to its caloric power.  All animals, given a choice between cooked and uncooked food of the same kind, choose the cooked — an indicator that the body knows something the mind hasn’t quite grasped.

There are plenty of accolades for Wrangham’s book,  from Edward O Wilson to Michael Pollan, from regular book reviewers to Professors of Evolutionary Biology.

You will be in good company and count your hours well rewarded in reading Catching Fire. You may even adjust the way you eat, lest you begin another line in the species Homo nextman!