Sleep is tied to recovery of normal function and memory formation. Why does it make sense, then, to stop for sleep just because the sun sets? Why not sleep just whenever we have a backlog of memories to form or we’re under stress or sick? Does the wide variation in our daily experience require such an extreme regularity of sleep regulation? Since we don’t learn or exercise the same amount each day, why do we nevertheless sleep the same amount? A number of possible answers are given in the first 10 minutes of this fascinating podcast, but offer your own insights as well.