I think every single one of those questions is missing yet another 'question' - that is, how much meat?

From a naive min-max approaching to building your diet, it generally pops up that -some- meat is super useful. Simply by doing that you ease all sorts of constraints on your diet, and allows you to optimize your veggies/grains for other stuff, instead of desperately trying to get all your iron and B12 in. Even from an overall energy budget point of view, -some- meat is super useful. There are large amounts of marginal land that is not really useful for large scale cultivation, but perfectly usable as feedland for free ranging animals.

The original article also conflates vegan and raw diets. I am a vegan who enjoys cooking and often eats highly processed foods; in my present environment (San Francisco), I'm faced with the health challenge of getting far too many calories every day, not too few. In fact, creative food entrepreneurs keep making this challenge worse and worse for me!

I would readily accept that almost everything about my life is drastically different from the environment in which my ancestors evolved. Those differences seem to have both positive and negative ethical and health consequences.

Resolving this is challenging. I've been on a ketogenic diet for the last several months, and while intellectually I recognise that eating mostly plants is more sustainable and has a lower carbon footprint, I have also never felt healthier than while eating larger amounts of fat and meat. My blood sugar is normalised, I generally have more energy and endurance and have effortlessly lost weight in the process.

I also find it hard to resolve the ethical dilemma of eating meat when my body responds so favourably to consuming animal fats. I think the least one can do is to make an effort to try to source locally produced free-range products, but sadly this is difficult for many as it's expensive or simply not available.

Some more variables: grass-fed or not, amount of fat, how rarely it is cooked, what organs are consumed.

Aquaponics ( http://en.wikipedia.org/wiki/Aquaponics ) exploits the nice relationship between fish excrement and plant growth (using some friendly bacteria to turn the amonia into nitrates) in a sustainable way that yeilds tasty lean meat.

> Err... bigger isn't always better, but I won't say no to a bigger noggin.

There is evidence that our heads would have kept growing if it wasn't for the fact that it makes it pretty likely that women will die in childbirth. So instead evolution got around this by having us born earlier, which is why we're basically born as fetuses compared to most animals. But there's a limit to that too of course.

As a matter of fact, cows were pretty late on the "domestication" game (around 3-4k years after pigs and sheep)[1].

Also, a lot of studies indicate that the kind of meat the humans ate when their brains grew was much more on the frog/bird/misc small animals side than on domesticated cattle.

[1] The edible story of food / Guns, germs & steel

> on the African savanna, where humans evolved

Um... answer's right there. Indeed this was the case on the African savannah, pre-agriculture.

We're no longer living in that environment. In the 21st century it's trivial to get sufficient calories, vitamins, and a balanced diet without eating meat.

Other points about our environment: (1) Relative to the African savannah, most of us burn many fewer calories per day. Fat asses in front of a computer instead of chasing down antelope, yanno. (2) We live 3x as long now, so our health concerns are different. That high-calorie blob of fat is tasty because it meant not freezing to death at age 16 and hence those taste buds were strongly selected for. Today we don't have that concern, and all those fat blobs may mean living to 60 instead of 80.

The survival needs of proto-humans on the savannah 100kya are not a very good guide to nutrition and health in the 21st century.

>When it's found in "soil", it's due to bacteria and small animals (insects, mites) that are in the soil.

I'm not sure what your point is.

>Any B12(-like) substances that are in plants (e.g., spirulina) are unlikely to be in a form that's bioavailable to human beings.

Yes, this is true.

>Vegans have to take B12 supplements of some sort or eat foods that have been fortified with B12. That's just a fact.

Modern vegans do need to take supplements, yes. The question is whether vegans in the ancestral environment would have gotten sufficient B12 from eating unwashed vegetables and roots. As far as I know, research is lacking on that point, but it is plausible.

And for the record, "produced industrially" means farming bacteria, effectively (per Wikipedia) - it's not synthetic or derived from meat.

(Some) nutritional yeast is fortified with vitamin B12. It's not a natural component.