"According to Richard Leakey, at around two thousand years ago, about half of the human population was supported by agriculture. By the eighteenth century, he estimates that as few as ten percent retained a hunter-gatherer lifestyle. “During the first eight thousand years of agriculture the number of people on the planet rocketed thirty times, from ten million to three hundred million.

"According to Richard Leakey, at around two thousand years ago, about half of the human population was supported by agriculture. By the eighteenth century, he estimates that as few as ten percent retained a hunter-gatherer lifestyle. “During the first eight thousand years of agriculture the number of people on the planet rocketed thirty times, from ten million to three hundred million.