Owl. Owl. Nocturnal. If you keep going, you'll go through nocturnal and wrap back around to lark. I assume that sleep-wake cycles plot neatly onto a populat

Owl. Owl. Nocturnal. If you keep going, you'll go through nocturnal and wrap back around to lark. I assume that sleep-wake cycles plot neatly onto a population standard normal distribution. Everyone on the early-riser half of the bell curve is larkish, and everyone on the late-riser half of the bell curve is owlish. As with most things, if you live more than 2 standard deviations from the median, you may sometimes experience problems arising from your deviation from the norm. Based on studies of people living in an actual cave with no timepieces or natural light sources, there may also be a component for the natural duration of one's cyclical body-clock. I suspect larks cycle faster than the median, and owls cycle slower, but I'm not aware of any supporting evidence for that.