So, the old chestnut: are humans adapted to be carnivores or omnivores? I
have to conclude, looking at all the evidence, that I believe that we are
definitely omnivores. My responses to the number of points made are below.

1. Gut shape etc
Our gut is NOT that of a carnivore (pace Barry Groves) or herbivore
(folivore) in terms of proportion. For the best discussion of this area,
see work by Katharine Milton, with an excellent essay in the fantastic
book by Harris and Ross (1987). Food & Evolution: Towards a Theory of
Human Food Habits. The most similar guts in proportion and structure (most
gut volume in small intestine) are the New World capuchin monkeys, and
also baboons. Both of these species consume high-quality, energy-dense
foods, which are not meat, but sugary fruits and protein-rich and
lipid-rich seeds. Animal meat and fat is an energy-dense food, but it's
not the only one. But Milton also makes the point that the gut is a very
plastic organ, with animal studies showing that a change in diet (incr
energy requirements, decr diet quality) can result in a change in gut
proportion. So the human gut as is could be a relatively recent
development.
Also worth saying, as Milton does, that the gut is very ancestrally
derived, so there is not an immediate correlation with gut and diet: eg a
cecum usually indicates a diet high in plant foods, but both the hippo and
the giant panda lack a cecum and they are strongly herbivorous.

Following on from Todd Moody's mention of Craig Stanford's point that
humans have, of necessity, followed an adaptational trajectory of
increasing carnivory, it may be that we are adapted to energy-dense foods,
that were originally fruits and seeds etc, but as our abilities with tools
and social organisation (hunting in groups) developed, we replaced one
energy dense food that was time-consuming to gather and each individual
had to do themselves with another that was easier and quicker to get.
Optimal foraging theory.

2. Ethnographic evidence for hunter-gatherer diets.
Dana Carpender cites Cordain et al.'s article in Am. J. Clin. Nutr.,
March, 2000, to provide 'evidence that we evolved on a meat-heavy diet
virtually devoid of grains, beans, and other concentrated carb foods.'
I have one slight caveat that using ethnographic evidence of HG diets as
an example of how we used to live can be dangerous, as HGs have been
marginalised by developing societies for several centuries at least, and
so what is representative in historical sources MAY not be representative
of Palaeolithic and Mesolithic populations.
But further than that, I take issue with the point that we have evolved on
a hunter-gatherer diet, as hunting and gathering as we now think of it in
a socially developed society is a relatively recent thing in human
evolution. We did an awful lot of eating and evolving as early hominids
(Australopithecus, early Homo), and so many of our dietary evolutions and
adaptations precede Homo sapiens sapiens society. Cordain et al, from my
reading of their excellent article, do not suggest that a meat-rich (>50%
energy) is the diet we humans evolved on, just what most hunter-gatherers
have eaten recently. They also make the point quite clearly that no single
diet represents all hunter-gatherer societies, which suggests to me that
we are well adapted to a varied diet, similar to other omnivorous
primates, and dissimilar to carnivores such as felids, or folivores, who
both have a much narrower diet composition.

3. Fossil evidence
The palaeontological and archaeological evidence is of course
inconclusive, given the small number and fragmentary quality of remains
over the last 5Myr. However, the dependence on meat is thought to be a
relatively recent development. Based on dental wear, most Australopithecus
are thought to have a wide ranging diet varying between fruits and leaves
(A. africanus) to tougher, more fibrous foods (A. robustus). Stable
isotope analysis provides some clue that Australopithecus was firmly
adapted to the grassland. Only coming into the Palaeolithic is the
dependence on animal resources increased (H neandertalensis and H
sapiens), and one could certainly argue that in the colonisation of
Europe, that is an adaptation to a colder environment, where
availability of suitable plant foods is reduced.

4. Physiological adaptations
Finally, physiologically, we still carry many of the traits that evolved
from our primate ancestry, such as an inability to synthesise Vitamin C,
very rare among non-primate mammals. This suggests that at some point, we
ate so much that we didn.t need to make it. So fruit must have been an
important part of our diet for long enough to lose that synthetic ability.
Todd Caldecott also makes a good point that fruits as we eat them now do
now necessarily bear much resemblance to wild fruits, being lower in fibre
and higher in sugar. This is also true for wild vs farmed animals. So just
eating what on the surface may appear to be a traditional diet may not be
what it would have been 1000's of years ago.


Think that's enough for now!
Off to have my well-balanced lunch of animal and plant protein, fat and
carbohydrate, all in moderation.

Tamsin

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Dr Tamsin O'Connell
Research Laboratory for Archaeology
University of Oxford
6 Keble Road, Oxford, OX1 3QJ, UK
tel:01865-283641
fax:01865-273932
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