Just quibbling - but I don't know of any vegan population the world except in recent times. Much of the world is vegetarian or nearly so (Chinese according to the China Study eat on average 1/10 the animal protein we do - so they're not close to being strict vegetarians like some Indians I know).

As an interesting aside my family was looking into organic / local beef just before going vegetarian. We're vegetarian primarily for the planet; but also for our health and lastly for ethical reasons. When peak oil hits all bets are off! Some land is best grazed; but the world has too many people and it would be best if we in the "first" world started having a one-child policy and not taking in immigrants. We're the biggest energy users and it's time we lead by controlling our own bloated population and also by reducing our energy use by 1/4 per person or much more.

Right now I'm kind of miffed that I upgraded our failing natural gas water heater with a 19 gal. electric one and it's cheaper to keep the tank hot and it's cheaper to run and it was 1/3 the cost to install; except it's about 15% higher in terms of CO2 emissions (yea our electricity is provided by a green company - Bullfrog - but dirty energy was used to put up those windmills ....).