Ed Yong writes: Evolution works on a strict energy budget. Each adaptation burns through a certain number of calories, and each individual can only acquire so many calories in the course of a day. You can’t have flapping wings and a huge body and venom and fast legs and a big brain. If you want to expand some departments, you need to make cuts in others. That’s why, for example, animals that reproduce faster tend to die earlier. They divert energy towards making new bodies, and away from maintaining their own.

But humans, on the face of it, are exceptional. Compared to other apes, we reproduce more often (or, at least, those of us in traditional societies do) and our babies are bigger when they’re born and we live longer. And, as if to show off, our brains are much larger, and these huge organs sap some 20 percent of our total energy.

“We tend to have our cake and eat it too,” says Herman Pontzer from Hunter College. “These traits that make us human are all energetically costly. And until now, we didn’t really understand how we were fueling them.” [Continue reading…]