[Introduction - 
In 2005, I saw a TV show "Searching for the Ultimate Survivor" on National
Geographic Channel which was about recent research in human evolution.   One of
the segments of the show featured Richard Wrangham (whose paper on tubers was
previously discussed in this group) talking about why he now thought both
meat-eating and cooking were probably important parts of human evolution.  
I contacted Professor Wrangham and he volunteered to send me some new papers he
has written and allowed me to post them here.   The one pasted below is the most
relevant one.   Any list member who emails me can receive all 3 papers in
formatted form (2 in Word including the full version of this one, 1 in PDF).
These are review copies and all publication rights are retained by the author,
Richard Wrangham, of course.  The following is as much as the list server will
allow me to post, email me for the full article.
      - Ken Stuart]


"The Cooking Enigma"

Richard Wrangham
Department of Anthropology, Harvard University
Cambridge, MA 02138

For Peter Ungar (ed.) 'Early hominin diets: the known, the unknown, and the
unknowable.' Oxford University Press (Human Evolution series).

This paper considers the role of cooking in the evolution of human diet. People
in every culture know how to make fire, and everywhere they use it to improve
their food (Tylor, 1878; Gott, 2002; Wrangham and Conklin-Brittain, 2003; Fig.
1).  But "No beast is a cook," as Boswell (1773) asserted. This difference
between humans and other animals has long been appreciated, and some have even
used it to define us: Boswell (1773) called humans the 'Cooking Animal.' But
while cooking is indisputably unique to humans, its evolutionary significance is
a matter of debate. There are two contrasting kinds of view.
The first, which is conventional wisdom, sees cooking as merely one of many
extra-oral food-processing techniques (such as pounding, grinding or drying)
that can raise food quality.  According to this view cooking may be valuable in
facilitating meal preparation but it is not important for understanding human
adaptation. For example, it would not be considered to have led to fundamental
changes in the human digestive system. In line with this idea, the ecological
impact of human diet choice and foraging strategies is often discussed without
considering the influence of cooking (e.g. Kaplan et al., 2000). Similarly,
studies of the evolution of human feeding behavior often focus on dietary
composition without considering extra-oral food-processing in general or cooking
in particular (e.g. Eaton and Konner, 1985; Ungar and Teaford, 2002). The
essential implication is that human biological evolution was not influenced in
any major ways by the adoption of cooking, and that evolutionists can therefore
ignore it.
The radical alternative is that cooking is a core human adaptation that has
importantly directed our evolution, or as Coon (1954) wrote, that cooking was
"the decisive factor in leading man from a primarily animal existence into one
that was more fully human." This perspective suggests that for humans, unlike
other species, cooked food is a need rather than an option. Accordingly, our
reliance on cooking results from certain features of human biology that have
evolved in response to the control of fire, such as our small guts, small teeth
and slow life-histories (Wrangham and Conklin-Brittain, 2003). From a dietary
perspective, it means that humans are distinguished as much by what we do with
our food as by the food sources themselves (whether meat, roots or grasses, for
example). In short, this view sees Boswell's characterization of humans as the
'Cooking Animal' as not only biologically but also evolutionarily significant
(Wrangham et al., 1999; Ulijaszek, 2002).
A few authors take an intermediate position. Notably, Brace (1995) has argued
that cooking is an important option that has led to limited evolutionary
effects, particularly a reduction in tooth size.
In this chapter I present arguments relevant to resolving this debate.
 
<1> Why cooking is expected to have evolutionary effects.
The contrasting views on the role of cooking agree in at least one respect. Both
acknowledge that cooking improves food. Some benefits vary across food types,
such as reducing physical barriers, changing molecular structure, reducing toxin
loads, and de-frosting (Stahl, 1984; Brace, 1995; Wrangham and Conklin-Brittain,
2003). Others appear to be consistent. For example, cooking leads to bursting of
cells, making food molecules more available. It also tenderizes meat and softens
plant foods, thereby making chewing easier. In addition, it reduces water
content and increases the proportion of edible material (Wrangham and
Conklin-Brittain 2003). 
Exactly how these benefits translate into fitness has not been well established.
However current data suggest that they may lead to significant energetic
savings. Thus, the cost of digestion is a high proportion of total energy
expenditure in all animals. In humans it has been measured at 405 calories per
day, or 18% of energy intake (Tataranni et al. 1995, 471 subjects). In other
animals the cost may be higher, e.g. up to 43% of energy intake in snakes (Secor
and Faulkner 2002). But the cost of digestion varies not only between species
but also with food quality. For instance high-protein diets increase the cost of
digestion by about 30% compared to high-fat diets (Westerterp et al. 1999).
Relevant to cooking, large meals that are physically hard cost more (e.g.
50-100% increase in cost of digestion in toads, Secor and Faulkner 2002). 
By softening food and reducing meal size, therefore, cooking can be expected to
reduce the cost of digestion, for example by accelerating the digestive process.
One measure of the rate at which foods are digested is the glycemic index, which
assesses the rate of appearance of glucose in the blood following ingestion. As
expected, the glycemic index is indeed consistently increased by cooking (Brand
et al., 1985; Bjorck et al., 2000). Experiments are needed to test the
hypothesis that proteins and lipids are also digested and absorbed more rapidly
in cooked than raw foods. If so, cooked food may prove to offer consistent
energy savings across all food types. Possible avenues for cost-saving include
reduced energetic cost per gram of food, reduced time for the gut to be
metabolically active, and a reduced size of gut needed to digest the food.
Evidence that cooking consistently improves food quality is suggestive in the
context of evolution because even a small change in food quality can have very
important effects. Among Galapagos finches, for example, a brief period of
ecological constraint that causes a shift in diet can lead to the rapid
evolution of larger or smaller beaks by natural selection (Boag and Grant, 1981;
Grant and Grant, 2002). Such evolutionary changes in digestive anatomy then
constrain future diet choices. Even minor changes in dietary adaptations, in
their turn, are known to have widespread effects on various aspects of species
biology. 
Chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla) offer an
instructive example of this process.  [... this section removed due to LIST
message length restrictions, but can be found in the full paper...]
The comparison of chimpanzees and gorillas thus illustrates how a relatively
small change in diet (an ability to survive on foliage without fruits) implies
substantial effects on biogeography, life-history and social behavior. Because
cooking is universal and has many effects on the diet, it can reasonably be
expected to have effects at least as large. For example, it should increase the
range of edible foods, and therefore allow extension into new bio-geographical
zones. Other things being equal, it should also provide a more predictable food
supply during periods of scarcity, because it enables a range of otherwise
inedible items to be utilized. It should have further effects by softening food.
For example, it should lead to a greater ability of adults to provision infants,
whose dentition is too immature to allow hard chewing, other than by giving
milk. It should likewise cause a substantial drop in the amount of time that
individuals spend chewing, with large consequences for the species activity
budgets (Wrangham and Conklin-Brittain, 2003).
In addition to raising food quality, cooking also radically changes the nature
of food distribution. Thus a species that cooks is obliged to assemble food
items into a location (onto or next to a fire) that is fixed for at least the
time that it takes to cook. Unlike the ordinary feeding pattern of any non-human
ape, therefore, this means that a cooking population is exposed to intra-group
competition over a valuable accumulated food-pile. Among other animals including
primates, the distribution of food is considered to be a key variable that
sculpts social relationships. For example, among chimpanzees by far the most
valuable type of concentrated food supply is meat. A successful hunt therefore
commonly leads to intense competition, including direct aggression and various
complex forms of social manipulation (Goodall, 1986). 
In short, the adoption of cooking is expected to be accompanied by a series of
large influences on various important biological systems, such as foraging
behavior, digestive strategy, infant development, geographical range and the
regulation of social competition. The fact that cooking is a human universal,
therefore, ought to be intensely provocative for students of human evolution,
since it raises the question of whether the practice of cooking has indeed
influenced these and other systems. 

[continued - Full paper available by sending an email to Ken's email address.]