I once read in Cosmo that men get sleepier post-orgasm than women do. Is this a bunch of bull? It's not like men crash after masturbating. Could it be attributed to physical exertion, rather than some hormonal response?
- name withheld,
Massachusetts

This is actually a well-documented phenomenon, complete with hundreds of Yahoo! Answers queries (my favorite response: "well probly idk mayb there jus bored lol") and a book called, yup, Why Do Men Fall Asleep After Sex? Even Arianna Huffington has weighed in ("Men go to sleep because women don't turn into a pizza," Men's Health editor Dave Zinczenko informed her.)

There's no hard-and-fast consensus yet, and physical exertion probably plays a small-to-middling role in the post-sex snoozathon, but the chief culprit seems to be

It sounds like just another uber-meltable cheese product, but Vavelta is actually miles away from anything you'd want to put in your mouth. It's a radical new treatment for facial pitting, scarring, and wrinkles made out of—what else?—newborns' foreskins. Foreskins have long been treasured by cosmetic dermatologists because they are rich in fibroblasts, tiny cells that play a crucial role in healing wounds and generating collagen and connective tissue.

A few weeks ago, Hanna Rosin's wrenching and well-researched article about young transsexuals—including a girl named Bridget (née Brandon), whose first words were "I like your high heels"—zipped around the blogosphere. In it, Rosin discusses the unsettling work of a psychiatrist who questions the scientific basis for allowing children to "transition" to the gender of their choice, citing several kids who emerged from their gender dysphoria after a rigorous course of therapy. "If a 5-year-old black kid came into the clinic and said he wanted to be white, would we endorse that?" he asks. The prospect of letting pre-pubescent pipsqueaks take hormone-blockers that might have far-reaching effects on their health and future fertility is indeed a little nerve-wracking.

But just on the heels of Rosin's piece, researchers based at Australia's Prince Henry's Institute this month released the results of the largest ever study of transsexual genetics, which compared the length of the androgen receptor (AR) gene in 112 male-to-female transsexuals and a control group of 250 "normal" men.

Nikon’s annual Small World Competition has been awarding prizes to the country’s best microscope-aided photography since 1977. The contest winners always present a reliably fascinating and freakish slice of life at a Lilliputian level. Last week, this year’s 115 winners were announced.

The cute and cuddly prairie vole, one of only a few mammals that remain monogamous for most of their lives, has long been a favorite “lab rat” for scientists studying love and attachment. Now researchers at Emory University and the University of Regensburg have found that prairie voles actually show signs of grieving—the opposite of attachment—when they’re taken away from their romantic partners.

It's been a hot week in the science of sex.

First of all, for all of you Intactivists out there (and I know there are a lot of you round these parts), a major finding might bolster your claim that routine circumcision isn't worth the risk.

It was only a matter of time before pop-news outlets pounced on a biological explanation for the tidal wave of bad credit and risky decisions that has engulfed the U.S. this month: it was those dang men and their raging hormones!

Welcome to the inaugural post of The Sex Files. Almost every publication worth its druthers has a sex column these days, full of Carrie Bradshawish musings about life and love, men and women, this and that. Here's our take on the genre. Instead of faux-sociology, we'll give you a broad view of new research and ideas in the sexiest of the hard sciences: reproductive biology, evolutionary anthropology, and genetics. This is sex from the inside out. Keep track of the column at popsci.com/sexfiles, where you can also sign up for an rss feed.

Disassortative mating alert! A group of European scientists led by Oxford biostatistician Raphaelle Chaix has provided some of the most compelling evidence yet that we humans pick our partners based on how different their immune systems—or officially, their Major Histocompatibility Complexes—are from our own.