For instance, too many young people today trim, shave, or wax too much of their body hair, both guys and girls. This is especially true for down-there hair, but you also see even young guys with shaved armpits. We have a gut reaction of "that just ain't right," and because these reflexes are the product of natural selection, we should at least take them seriously rather than toss them aside as mere superstition.
How might this lack of body hair further deflate the already flaccid sex culture of the past 20 years, as compared to the 30 years before that?
Imagine you're a boy or girl coming of age and during your first real-life view of a nude body, you don't see any bush. That has to be one of those fixed-action patterns that ethologists talked about -- like when a predator sees an image that resembles his typical prey, he reflexively lunges at it, even if he's raised in captivity and has never seen his prey for real. When you first behold the sight of a naked girl (or boy) with pubic hair, some chemical cascade must go off in your brain, switching you from still-growing-up mode to get-down-to-business mode. Lacking exposure to that powerful visual, you don't get quite so out-of-control.
Aside from real-life girls, what about real-enough girls that most boys will see first, in some pornographic context? Just compare a typical Playboy Playmate from 2008 to only 20 years before in 1988. There's a primal response to the sight of bush that makes the 2008 girl look de-sexualized, like Rapunzel after the witch cut off her flowing braids. That first big reveal is supposed to provoke your teenage curiosity and create a sense of mystery about the other sex -- I wonder what it looks like! If what you see is not at all different from when you played "I'll show you mine if you show me yours" way back in pre-school, you can't help but feel that the other sex isn't quite as fascinating as you'd hoped they would be.
And don't forget the role of scent. Hair holds in whatever is going on down there -- sweat, pheromones, etc., all of which play a role in human signaling. For example, a famous psych experiment showed that other people can tell when a girl is ovulating because they rate the scent of her underwear as more pleasant when it came from that phase than from the non-ovulating phases of her cycle. (This study was done in the '70s -- surprised?) Several recent studies show that we prefer the body scent of people who have different variants of genes than we do at a spot in the genome called the MHC, which is involved in immunity. The more diverse we are at that location, the less likely it is that pathogens will have already seen our combination before, so they won't have an immediate lock on our position to exploit us. Thus, preferring a mate with a different profile from ours helps to make our offspring more robust against infectious disease.
But just how are we supposed to tell that some girl is ovulating, or that someone would make a great match for us at the MHC locus, if we can't get a good feel for their body scent? Lack of hair to trap the scent in must really mess up the lines of communication between the sexes.
Zooming out, the lack of hair and therefore of scent drastically changes the larger environment we live in. It's not just the scent of this partner or that one that throws the "time to grow up" switch on in our brain -- it's also what we perceive about the community we live in. Does it smell like people are very sexually active? Well, maybe it's time to grow up and get to it ourselves. If it doesn't, then maybe it wouldn't hurt to put it off for awhile longer until it becomes more urgent. Via Ray Sawhill's blog, here's a look back on New York in the 1970s. Excerpt:
What do I remember most? The smell; pretzels, piss, sweat and sex. Yes, in 1978 New York actually smelled like sex. At the time I didn’t have a name for the smell, but I recognized it, was excited by it, was intoxicated by it.
30 years later New York is changed. The smell of piss is occasional, rather than pervasive. The smell of sex is gone. I don’t find myself in the neighborhoods where the pretzel wagons ply their trade that often. The city is safe.
And it’s a little boring.
Young people growing up today can just smell that their world isn't very wild; they don't need to conduct a random survey of their society. What little activity is going on no one will know about because the overall level of body scent in an area has been dampened by the decline in body hair. It's almost as though people were trying to cover up their tracks or keep others from knowing what they're up to. Where there's no smoke, there can't be fire.
Bottom line: pubic hair is a secondary sex characteristic, i.e. one that develops only during puberty, so messing around with it would be like playing around with other such traits. A girl wouldn't want to lose her hips and look like a little boy again, would she? A guy wouldn't want to lose his jawline and look like a little girl again, would he? I think the same must apply to underarm hair as well, although I realize we're past the cultural point of no return for girls shaving under their arms. Sure, it looks better visually, although the look would not change much if girls merely trimmed it down to an inch or two, plus you wonder what we've done to the richer set of experiences we're supposed to have.
Other body hair is more of a mixed bag since it's not as universal -- while everyone gets hair around their stuff and under their arms, hair elsewhere can vary a lot from one person to another, suggesting that it's not so crucial for survival and reproduction as is universal hair (including head hair). Messing with that doesn't seem like it would matter much, but keeping your pubic and underarm hair as close to natural as possible seems to be the best plan.