Thursday, March 28, 2013

Richard Wrangham, Catching Fire: How Cooking Made Us Human (2009)

Edward O. Wilson's research on eusociality led him to identify the nest as a common attribute among the eusocial species.  Although not proven, Wilson surmises that a gene has been suppressed among the eusocial species that silences the brain's program for dispersal from the nest, leading to the sustained survival of the eusocial community.  (September 12, 2012 post)  Humans are included among the eusocial species, but humans disperse; they do not build and congregate in nests, but they do build and maintain social communities comprised of multiple generations and humans are organized into groups by altruistic division of labor, which are characteristics of eusocial species.  As a surrogate for the nest, Wilson suggests that the campfire served a nest-like function in the development of the genus homo, which strongly suggests that  mastery of fire was critical to humans eusociality. 

As I read Wilson's The Social Conquest of Earth (see September 12, 2012 post), I was reminded of a book on the bookshelf that addressed this topic, Richard Wrangham's (see  July 1, 2010 postCatching Fire: How Cooking Made Us Human.  Wrangham believes that mastery of fire was critical to human evolution, but even more important, mastery of fire enabled early humans to cook their food on a regular basis. According to Wrangham, cooked food is even more significant than mastery of fire for human evolution.  Armed with data and concrete examples Wrangham demonstrates that eating cooked food is linked to two evolutionary changes in the human body:  (1) comparatively smaller, more efficient digestive systems (particularly the stomach and the small intestine) that require less energy to digest food and absorb nutrients than our predecessors, and (2) larger brains.  Large brains require significant amounts of energy, and that energy is available to the brain only if it is not needed for other activities essential for survival such as eating and digesting.  Compared to apes and chimpanzees (and presumably extinct australopithecines and habilines), humans spend a fraction of their daily life eating and digesting food.  Apes and chimps spend hours eating plant food or fruit every day.  The relative weight of the human gut is roughly only 60% of the relative weight of the gut of apes and chimpanzees.

The controversial question is when did the first species among the genus homo begin cooking food?  For certain the benefits of and development of a preference for cooked food was accidentally discovered.  Wrangham believes that human cooking begins with homo erectus.  There is anthropological evidence cited by Wrangham that cutting meat with primitive stone tools began as early as 2.6 million years ago.  Roughly 300,000 years later, a new species, referred to by some as homo habilis, which still had many australopithecine characteristics, emerged, and roughly another 500,000 years later the species referred to as homo erectus, emerged according the available fossil record and lived on the African continent for nearly 1.5 million years (until roughly 300,000 years ago).  While it is doubtful that homo erectus had language capacity or skills (see January 31, 2013 post discussing homo neanderthalensis), what we do know is that the cranial capacity of early specimens of homo erectus was 200cc greater than homo habilis and later specimens 400-500cc greater than homo habilis, representing an increase in brain size of approximately 33-75% over the habilines.  (See November 21, 2012 post).  That would be the largest incremental percentage increase from species to species within the genus homo. Homo erectus is recognized to be, in many respects, to be much closer to modern homo sapiens than homo habilis.  Combined with some evidence of the use of controlled fire at sites where homo erectus bones have been found, the control of fire and the significant increase in brain size (the energy for which is enabled by decreased energy used in eating and digesting food) lead Wrangham to identify homo erectus as the first human species to favor and consume cooked food on a regular basis.  Wrangham also speculates that homo erectus, unlike its predecessors, favored sleeping on the ground (instead of trees) and the control of fire would have been useful in providing light to see predators at night or keeping predators away.  The morphology of erectus is not as suitable for sleeping in trees as its predecessors.

Others (Aiello and Wheeler) have concluded that cooking food is the invention of homo heidelbergensis (the predecessor to homo neanderthalensis) a later species.  Aiello and Wheeler believed that brain size was steady among homo erectus until the emergence of heidelbergensis with its larger brain.  Wrangham finds the fossil record sufficient to support the view that brain size gradually grew among erectus and believes that the steady increase in size is attributable to improved cooking techniques, and that continued growth in brain size to heidelbergensis and ultimately to homo sapiens is likely similarly associated with improved cooking techniques, not cooking as a novel adaptation or spandrel. 

Wrangham's thesis is this:  "An important step in fire's becoming a central part of human lives was to maintain it at night.  Suppose some habilines carried a smoldering log by day to protect against predators, then left it at the base of a sleeping tree when they climbed to make a nest at night.  It would not have been such a big step to give it extra fuel so the log will still be burning the next day --perhaps after seeing this happen first by accident.  From there it would have been a smaller step to sitting near the fire to keep it burning, and thereby take advantage of its protection, light, and warmth.  Once they kept fire alive at night, a group of habilines in a particular place occasionally dropped food morsels by accident, at them after they had been heated, and learned that they tasted better.  Repeating their habit, this group would have swiftly evolved into the first Homo erectus.  The newly delicious cooked diet led to their evolving smaller guts, bigger brains, bigger bodies, and reduced body hair; more running; more hunting; longer lives; calmer temperatures; and a new emphasis on bonding between females and males.  The softness of their cooked plant foods selected for smaller teeth, the protection fire provided at night enabled them to sleep on the ground and lose their climbing ability, and females likely began cooking for males, whose time was increasingly free to search for more meat and honey."  So despite the relative dearth of evidence of fire dating back to the time of homo erectus, Wrangham believes that the dramatic shift in brain size and tooth size is significant evidence that Homo erectus started the first outdoor cooking kitchen. 

Division of labor by sex.  E.O. Wilson also includes altruistic division of labor among the attributes of eusociality (September 12, 2012 post).  Wrangham has a discussion that dovetails with Wilson on this point.  First, cooked food liberated males to spend more time hunting for meat in a way that chimps and apes cannot because they spend so much time chewing their food.  Fire enabled men to confine their eating time to the hours around dusk and even after dark.  Hunting enabled the male to contribute food to his family (including an extended family group), but this effort was ultimately dependent upon a reliable, predictable economic exchange between women and men.  Women became foragers and this provided a reliable source of food energy in the event that the men of the group returned with no meat.  Women also became primarily responsible for cooking.

Wrangham argues that while relying on cooked food created opportunities for cooperation, more importantly it exposed female cooks to exploitation because cooking takes time and lone cooks could not easily guard their wares from thieves.  This problem was solved, Wrangham believes, by pair-bonds among males and females:  a "husband" ensured that the woman's gathered foods were not taken by others and from this evolved "a simple marriage system." The male provided the female (and their children) with meat.  Consistent with Boehm's observations (see November 21, 2012 post), Wrangham observes (based on anthropological evaluation of modern hunter-gatherers) that meat is actually shared among a larger group that includes not only the male's "wife" and children, but also an extended family (and possibly a stranger).  The female's distribution of gathered food is largely shared just with her "husband" and their children.  In the gathering of food, there may very well be cooperation among women, but the sharing of the gathered food is limited to the immediate family.  Presumably sharing meat among a larger group evolved because direct reciprocity is essential to the hunting and killing of the large animal, bringing the meat back to the campfire and slaughtering it. 

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