What, though, if the drop in teen pregnancy isn't a good thing, or not entirely? What if there's a third explanation, one that has nothing to do with just-say-no campaigns or safe-sex educational posters? What if teenagers are less fertile than they used to be?
Not the girls—the boys?
The great sperm-count debate began in 1992, when a group of Danish scientist published a study suggesting that sperm counts declined globally by about 1 percent a year between 1938 and 1990. This study postulated that "environmental influences," particularly widely used chemical compounds with an impact like that of the female hormone estrogen, might be contributing to a drop in fertility among males. If true, this was obviously an alarming development, particularly given that human sperm counts are already strikingly low compared to almost any other species. "Humans have the worst sperm except for gorillas and ganders of any animal on the planet," points out Sherman Silber, a high-profile urologist who attributes this in part to short-term female monogamy. Since one man's sperm rarely has to race that of another man to the finish, things like speed and volume are less important in human sperm than in other animals, permitting a certain amount of atrophy among humans.
Among the evidence presented are several trends that seem to point to a subtle feminization of male babies: a worldwide rise in hypospadias, a birth defect in which the urethral opening is located on the shaft of the penis rather than at the tip; a rise in cryptorchidism, or undescended testicles; and experiments Swan has done showing that in male babies with high exposure to compounds called phthalates, something called the anogenital distance is decreasing. If you measure the distance from a baby's anus to the genitals, the distance in these males is shorter, more like that of...girls.
Huh. And here I was going to blog this morning about (what I perceive to be) the astronomical increase in casual sex as a result of the internet (vis a vie craigslist, myspace, but certainly not facebook since that encourages people to "poke" each other).