Y: Don, do you ever daydream about a different biological clock? I mean it's the same thing day in and day out with our circadian clocks: twenty-four hour cycle of light and dark, we sleep, we wake, we release hormones, our body temperature changes.

D: Well, I don't know. I'm pretty content.

Y: But have you thought about all the options out there? Did you know there's a type of marine worm that, along with following a circadian clock, follows a lunar clock? Its spawning is influenced by the thirty-day moon cycle.

D: I do know that bees have unusual biological clocks, too. They change their clocks depending on their job in the hive. Nurse bees forgo the circadian cycle when they care for larvae night and day, while foragers follow regular circadian cycles. If the bees switch roles, the nurse-turned-forager will start following a circadian clock again, and the forager-turned-nurse will stop.

Y: And then there are Mexican blind cavefish.

D: What about them?

Y: Counter intuitively, from a molecular standpoint their circadian clocks seem jammed in perpetual daylight.

D: That reminds me of Arctic reindeer, since they live in perpetual daylight in summer and perpetual darkness in winter, they've lost their circadian rhythm.

Y: There's also the forty-seven hour cycle of the Somalian cavefish. They haven't seen light in over a million years, so their clocks no longer respond to a twenty-four hour cycle. Scientists think they may be responding to cyclical changes in the caves.

D: Well, I guess there's a whole world of biological clocks out there that I hadn't explored. Yaël, I'm going to make a bad pun now---are you ready?

Y: Go for it, Don.

D: So many clocks, so little time.