I am sure I have read it somewhere, but I can't figure out in which book anymore (I think Steve Pinker's How the Mind Works)
Most of human (pre-)history (and evolution) has happened in a foraging economic and social context. What surface area was required per person for a hunter-gatherer society to thrive? Since the ideal environment for foragers was the Savannah (c.f. Pinker), we could take this as a default ecosystem to compare to other environments, like steps or jungles.
Any numbers? Thanks.