They're using efficiency in a different (and certainly confusing) sense. Their gas guzzling car example explains their thought process: humans, whilst hunting,

They're using efficiency in a different (and certainly confusing) sense. Their gas guzzling car example explains their thought process: humans, whilst hunting, are running hot. They're inefficient at the task of maintaining themselves between meals. That's made irrelevant by the fact that they're collecting more food on average, so they're actually more efficient overall, but that only becomes true once you factor in food intake. Sort of like saying that a lorry is a less efficient way to travel than a car. True until you mention that the lorry has many tons of cargo which must make the journey with you (or in subsequent trips), _then_ the reverse holds.