Although Tom Billings article on comparitive biology on Beyondveg.com contains some good information, I would like to make a few remarks on that article. Unfortunately, I can't quote him because he copyrighted his article and I don't want to contact him for permission since I don't agree with that policy. People can feel free to react to this post, but a response is not extremely likely, since I have more things I like to do with my life.

Tom is reacting to a claim of the raw vegan movement that meat eating does not affect reproduction, hence it can not affect evolutionary selection. Tom is writing that this claim shows misunderstanding and ignorance of how evolution works because of a misapplication and limited examination of the principle of survival of the fittest. He says that it is a mistake to consider survival of the fittest on an individual short term basis and that it is really a broad based, multi- generational proposition. Since meat eating has become part of our long term environment, selective pressures will favor genes that are best adapted to that environment, leading to adaptation of meat eating (according to Tom).

Let us now see what the neo-Darwinist point of view is on this. Survival of the fittest is a misleading term, since it suggests that survival is the key factor, while fitness is best approached with reproductive success. Tim Clutton-Brock, a respected zoologist from Cambridge University, made a huge compilation on reproductive success studies in wild animals, called "Reproductive Success", published by Chicago University Press in 1988. This book gives a good insight in contemporary evolutionary theory. It explains that evolution, which is the possibility for selection, can only happen if genetic variation leads to differences in individual Lifetime Reproductive Success (LRS). This means that something that becomes part of our long term environment, like vertebrate meat eating (which is only possible since the use of tools), is only going to lead to adaptation if it is caused by genetic variation that leads to differences in LRS. So if meat eating does not affect LRS, there is no possibility for adaptation. So Tom's criticism to the raw food vegan claim stated earlier, shows that Tom is the one who shows misunderstanding and ignorance of how evolution works.

So let us now look at the "proof" for adaptation to animal foods that Tom brings up. We have to keep in mind that we are talking of animal foods in the form of vertebrate meat, since the inclusion of invertebrates in the diet doesn't require such specific adaptations as vertebrate meat does. I will list all the "proof" items and give a short comment.

B12: only animal foods contain B12.
Irrelevant, since it is provided by soil and insects on plant foods.

EFA: plant foods are poor sources of EFA, with the exception of some rare sources.
Irrelevant, since there are still plant food sources that contain EFA (and invertebrate sources?).

Taurine: low rates of taurine synthesis in humans compared to herbivores.
Irrelevant, since it doesn't show a genetic change: the possibility to synthesize it is still present in humans. It might just be put on low rates because of the intake of taurine with the HABIT of eating vertebrate meat.

Beta carotene: slow conversion of beta carotene to vitamin A in humans compared to herbivores.
Irrelevant: see taurine.

Zinc & Iron: plant foods available in evolution were poor zinc and iron sources.
Irrelevant, since there are still plant food sources (plus invertebrates?)

Bitter taste: experience of tasting bitter in humans comparable to carnivores/ omnivores.
Irrelevant, since there is no way to measure this objectively.

Heme iron: humans have specific receptors for heme iron, which is almost only found in animal foods.
This is the only point that might show adaptation to vertebrate meat. However, "almost" could be the operative word here: since plant foods are not totally void of heme iron, there could be receptors for that source. Also, if heme iron is present in invertebrates, this point is irrelevant (does anyone know if this is the case?).

I am not a professional in comparative biology, but since vertebrate meat requires specific adaptations, it might be useful to compare some traits of humans to vertebrate meat eaters. The following differences might indicate that humans are not adapted to vertebrate meat eating:

The liver of vertebrate meat eaters can detoxify vitamin A, while the liver of humans can't.

Stomach capacity of vertebrate meat eaters is 60 to 70% of the total volume of the digestive tract, while in humans this is about 25%.

Length of the small intestine of vertebrate meat eaters is 3 to 6 times the body length, while in humans this is 10 to 11 times the body length.

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