Since the Wrangham hypothesis has been mentioned again, maybe this is a
good time to discuss it once more.  It is linked to the "Expensive
tissue hypothesis" of Aiello and Wheeler.  According to the ETH, one of
the key adaptations that differentiates humans from other primates is a
smaller ratio of gut to brain mass.  The reason is this:  Brain (nerve)
tissue and muscle tissues are both "expensive" in that they require a
lot of energy to run.  There are three kinds of muscle tissue: skeletal,
smooth muscle, and heart muscle (see
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20102/Bio%20102%20lectures/Animal%20cells%20and%20tissues/Animal%20Tissues.htm
for example).  The gut has a lot of smooth muscle.  The ETH says that as
we developed larger brains we had to have shorter guts.  This, in turn,
means that we needed higher-density foods, foods that deliver more
energy per unit of weight.  The gorilla subsists on a diet of mainly
low-density foods, primarily foliage, and a long gut is needed to
extract all the nutrients from this sort of food.  If you can imagine
going on a "gorilla diet", you'd be eating mainly lettuce and cabbage
and similar things, topped off with a few bugs, larvae, and the like.
Since this food is low-density, gorillas have to eat almost
continuously.  If we tried it, I think most of us would experience
pretty severe gastric distress, pretty quickly.  Our guts are not large
enough to handle that volume.

High-density foods are meats, nuts, starches, and fruits.  It is a
commonplace theory that meat had to play a more important role for
hominids and early humans, initially from scavenging and later from more
and more effective hunting.  Fruit, once you've left the tropical
forests, is only seasonally available.  So the question is whether the
transition from apelike hominid to human-like and eventually human, and
the concomitant shortening of the gut, was driven mainly by eating more
and more meat or whether high-density plant foods played a key role.
The Wrangham hypothesis is that plant foods did play a key role,
especially in the form of roots and tubers, and especially cooked.  See
http://cogweb.ucla.edu/Abstracts/Pennisi_99.html

As you can see from that essay, the whole thing remains controversial.
A big part of the controversy is the question of just when humans and/or
hominids started using fire for cooking.  This question remains
unanswered.  The human species (i.e., humans anatomically like us) is
believed to be 150,000-225,000 years old.  The earliest evidence of
cooking hearths is 250,000 years old.  I think it's important to note,
therefore, that humans have *always* cooked, for as long as there have
been humans.  Remember that the paleolithic era ends only about 12,000
or so years ago, so any claim that cooking is "unpaleo" must be
rejected.  If the paleo diet is to include what paleolithic humans ate,
then it would include cooked food.  One might want to restrict the
"paleo diet" to what pre-human hominids ate, but I'm not sure what the
rationale would be for doing so.

And as you can also see, there are those who believe that the evidence
points to much earlier dates for the start of controlled use of fire and
thus the possibility of cooking.

Note that the tenability of the WH is not an all-or-nothing choice.
Wrangham pointed out in his article that while some tubers are inedible
raw, others are quite edible.  Fire, whenever it became available for
cooking, would not have *introduced* tubers into the hominid diet; it
would have simply made more of them available.

Todd Moody
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