In time for Valentine’s Day, it seems appropriate to explore the practice of “hooking up.” The term has varying definitions, but, for our purposes, we will vaguely define it as engaging in any type of noncommittal sexual relations with another person or persons for non-procreative purposes.

Although premarital sex — which would fall under the definition of hooking up previously put forth — has been described as “universal” for both sexes in 50 percent of preindustrial cultures and is documented in 80 percent, it has become the downfall of our generation. Cultural commentators, often invoking their deity for support, unconvincingly decry it as an immoral metastasis from the unrestrained hedonism of the 1960s, as an outgrowth of a decline in loyalty to religious teachings, or as one of the products of an excessive focus on career at the expense of time-consuming personal relationships.

But they are right to see it as a major part of the Zeitgeist with significant social implications. According to a 555-person study by psychologist Elizabeth Paul, 78 percent of students have “hooked up,” and each respondent averaged a chimpanzee-ish 10.8 romantic partners apiece. It is clear that an unprecedented number of undergraduates are engaging in short-term mating strategies relative to earlier generations (e.g. that of the 1950s), and they seem to be doing so for reasons that are mostly opaque.

Solving this puzzle is not easy. Colleges and universities have changed institutionally, mores have evolved in multifarious and interdependent ways and the student body is nothing like it once was. Today, one finds much more equity in the classroom — a fact that is to be applauded. In 2003, 58 percent of all bachelor’s degrees and 59 percent of all master’s degrees were awarded to women, according to the National Center for Education Statistics. In 1969, the situation was reversed, in favor of men. And this demographic inversion of the sex ratio at colleges and universities, for reasons given below, may be a major factor to consider in the ascent and hegemony of the “hook-up” culture in modern college life.

Support for this view comes from the laborious work of ethnographers and psychologists who have studied gender ratios and human sexual strategies. In 1991, F.A. Pedersen analyzed the variability of sex ratios in the United States and found that increases in numbers of men in a population is associated with an increase in monogamy and that an increase in the number of women resulted in a corresponding increase in short-term mating behavior, such as hooking up. In a massive cross-cultural study of 48 countries that was published in “Behavioral and Brain Sciences,” S. Schmitt investigated this phenomenon globally and found that as the ratio of women to men increased, there was a nearly linear increase in the prevalence of short-term mating behavior.

But how can we explain this? This tendency appears to be derived from the fact that — on average — men and women have different sexual desires and incurred costs based on the wildly different number of offspring that they can have. A woman can have only one child per year, while a man could theoretically have an infinite number. Since, generally speaking, living things act to increase their reproductive success, almost always unconsciously, this leads to women wanting longer-term relationships and commitment from a high-quality mate (to make that one child as “fit” as she can) while men seek more short-term copulations to maximize their number of offspring. But when good men are relatively harder to find, women are more likely to give in to the male desire for “hookups” in order to attract what in this situation is a scarce resource. And the opposite is also true; when males are abundant, women are — as they can afford to be — very choosy.

I do not mean to suggest that this shift in the male-female ratio completely explains the phenomenon of “hooking up.” But in a favorable closed cultural environment, it may be part of the story. There are certainly many other issues to consider: intrasexual variations in mating strategies and competition, the actual effective size of the mate pool (number of available desirable partners), changes in undergraduate goal structure, cultural influences from other institutions and many more. I welcome objections and criticisms of this idea. But I think it is a good bet that, traveling the spectrum from mostly-male colleges to mostly-female colleges, this secular trend of increasing promiscuity will hold independent of these other factors, and I hope to test this idea empirically. (For the record, Quinnipiac is 61 percent female.)

In closing, let me say that I am not making any value judgments on “hooking up” one way or the other. I am not blaming women for anything (blame DNA), nor am I a misogynist, a racist or a rape-monger, names I was called after writing a column about how understanding biology can be used to stop rape. Nor do I propose that colleges do anything about this demographic trend — except rejoice. I shouldn’t have to say this, but apparently I do. Hooking up is a curious practice, and all I would like to do is get to the bottom of it.

Matthew Gillum is a first-year graduate student in molecular and cellular physiology. His column appears on alternate Fridays.