Early birds may get worms but not chicks. That is, according a recent study by Davide Piffer at the University of Pisa, the mean number of sexual partners for morning-oriented men was 3.6 versus 16.3 for evening-oriented men. This means that guys who are night owls have about four times as many sexual partners as morning birds.

Drawing on evolutionary psychology, Piffer offers a few theories:

1.) Throughout human history social activities have taken place at night. (In fact >60 percent of the people Piffer polled met their latest partner in the evening or night.) The evening is commonly reserved for courtship activity — dancing, drinking, having sex. Over time, the male night owl attends more social events, meets more women, and has more sex.

2.) “Eveningness” is a sexually dimorphic trait. Across cultures, “more males than females stay up late at night (due to biological differences involving the timing of peak melatonin levels). Piffer speculates that men evolved to stay up late because, in the deep past, the most reproductively successful males were night owls and they passed along their genes to subsequent generations. In terms of Darwinian sexual selection, evening orientation benefits males more because it gives them an increased opportunity to acquire multiple lovers — all at one go, or over time. Women, however, don’t achieve greater reproductive success by having sex with more men (it only takes one to get pregnant), which is why fewer women are evening-oriented. Men with an evening orientation have a competitive advantage over men with a morning orientation.

3.) Evening-orientation, Piffer speculates, may also be a direct product of sexual selection. That is, women may actively choose night owls over morning birds. Piffer draws on the “cads-versus-dads” theory; that is, women often go for bad boys, especially at a certain stage of life, and men who stay up into the night are likelier to fall into this category.

4.) Being a night owl may also be a form of “handicap signaling.” Staying up late at night (possibly drinking and smoking) can take a toll on one’s health. Only a man who is fit and healthy would be able to compensate for his lifestyle. Assuming a man seems unaffected by little sleep, his evening orientation indicates a strong constitution — a sexy quality.

Mind you, Piffer’s theories are allextremely speculative (but fun!). Of course there are many unanswered questions: By nature, is there something about a night bird’s personality that makes him more promiscuous than a morning bird — or is it only that he has more opportunities to meet women? Do night owls in all cultures get more sex? The study took place in Italy — it would be interesting to repeat the same experiment in non-Western cultures.

At least this may explain the otherwise inexplicable female obsession with vampires.