So why do we have to sleep, anyway? I hate spending almost a third of my life in a coma. –Bill Toman, Madison, Wisconsin

Why? It helps you understand what it’s like being president. Besides, what else are you going to do at 4 AM? The truth is, researchers don’t know why we have to sleep. They have theories out the wazoo, though. For example:

(1) Sleep restores. In other words, “sleep either allows or promotes physiological processes which rejuvenate the body and the mind,” as one researcher puts it. Studies suggest sleep restores neurons and increases production of brain proteins and certain hormones.

(2) Sleep conserves energy. It takes a lot of energy to keep us warm-blooded critters warm. Since energy consumption drops during sleep, maybe we doze so we don’t have to eat all day long (not that that stops a few people I could name). Supporting this theory is the fact that cold-blooded animals have a much less regular sleep-wake cycle.

(3) Sleep keeps you out of trouble. No kidding. Says here, “according to this theoretical position, prehistoric mankind adapted the pattern of sleeping in caves at night, because it protected humans from species physiologically suited to function well in the dark, such as saber-toothed tigers.”

(4) Sleep helps you remember. In other words, it gives the brain a chance to process the day’s experiences and file them away in the memory. Thus we remember things learned just before sleep better than things learned earlier.

(5) Sleep helps you forget. Unlearning during sleep prevents the brain from becoming overloaded with knowledge. Judging from my mail, not a critical problem for most people.

Complicating matters is the fact that some people thrive on virtually no sleep. In 1973 British researchers reported on a 70-year-old woman who claimed she slept only an hour a night with no daytime naps. In one 72-hour test, during which she was under constant watch, the woman stayed awake 56 hours, then slept only an hour and a half. Yet she remained alert and in good spirits.

According to one study, short sleepers (six hours or less per night) are well-organized, efficient, ambitious, decisive, and self-confident–in other words, totally obnoxious. This suggests the real function of sleep is to let the short sleepers get the jump on the rest of us. Next time your lids get heavy, therefore, think: the short sleepers are out there, smirking.

Where does the expression “mind your P’s and Q’s” come from? Does it mean politeness and quietness? Also, I recently came across the phrase “a labor organizer traveling on the q.t.” What does q.t. stand for? –Kimberly Taylor, New York City

As usual, we’ve got lotsa theories, no facts. The more fanciful explanations for “mind your p’s and q’s” include:

It originated in British pubs as an abbreviation for “mind your pints and quarts.” Supposedly this warned the barkeep to serve full measure, mark the customer’s tab accurately, etc.

It meant “mind your pea (jacket) and queue.” Queues (pigtails) were often powdered, and wifeypoo was telling hubby to keep the cruddy kid stuff off his collar. An even dumber variation of this involves “pieds,” French for “feet,” and says minding your p’s and q’s means combing your hair and polishing your shoes, or something like that. Sure.

P and q stands for “prime quality.” According to the Oxford English Dictionary, to be P and Q was a regional expression meaning top quality. It first shows up in a bit of doggerel from 1612: “Bring in a quart of Maligo, right true: And looke, you Rogue, that it be Pee and Kew.”

The simplest explanation is that the expression refers to the difficulty kids have distinguishing lower-case p and q, mirror images of each other. Mind your you-know-whats was thus a teacher’s admonition to students. Plausible? Yes. Sexy? No. Being a slave to facts is such a drag.

“On the qt,” meaning on the sly, secret, is easier. Most likely it’s an abbreviation of “quiet.”

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.

Cecil Adams is the world’s most intelligent human being. We know this because: (1) he knows everything, and (2) he is never wrong. For more, see The Straight Dope website and FAQ.