There's other variations too. Say you need some X and a lot of Y. But X is rare and Y is plentiful. Evolution leads you to an insatiable drive for X but not for

There's other variations too. Say you need some X and a lot of Y. But X is rare and Y is plentiful. Evolution leads you to an insatiable drive for X but not for Y. Then, suddenly mankind figures out how to cheaply produce X, e.g. salt and sugar. Another- suppose food supplies are variable and insecure. The optimal amount of muscle & bone is exactly what you need and no more, and the optimal behavior is to be as active as required and no more. Viola, you get humans, one of few species whose bodies require ongoing training to stay fit & healthy, while paradoxically being quite lazy.