Our brain is the defining feature of our species. And we pay a price, if you will, to have a brain like ours. So how could we possibly get where we are without evolving a very elaborate system to make sure you never run out of energy? That's what we had to do. If you look at primates today, right, these would be our nearest evolutionary relatives. They don't have this capacity. When you overfeed humans, we get fatter. But from an evolutionary perspective, it's important because muscle is a lousy source of energy. Fat is not fat is a wonderful source ofenergy.