I would like to respond to JJV's post below in two ways.
First, the short answer.
Slightly longer answer, in a sort of silly high-pitched whine:
Fortunately, the Bible on the Internet weighs less so I took the time to read the (brief) story of Cain and Abel. Cain was a farmer and Abel was a shepherd. Unless there was a taboo (shared by the only four people on Earth at the time, although the odds of that are relatively good) against eating what you yourself raised, the suggestion appears to be that Cain was a vegetarian and Abel was a carnivore, based at least on what they offered God. (That God was picky in re sacrifices suggests a divine thumb on the scales, but maybe He was an early advocate of population control but hadn't necessarily thought His initial solution through.)
However, JJV is to be complimented on staying consistent with the original Economist article, which allows the reader to draw whatever conclusions may be desired based on the blunderbuss style of writing displayed therein. To take the most readily available target, to suggest that a relatively radical switching of diet would have adverse effects on initial generations not only breaks no new ground, but paves over old ground with substandard asphalt. Or maybe it does donuts on the ground. Mmm, donuts. If we had gone straight from mammoth to Krispy Kreme it's a safe bet we wouldn't have made it too far, except for inventing the wheel and the cryptic-to-future-archeologists phrase "Hot Donuts Now."