Of COURSE this awesome paper would blow up the internets on a Monday, and of course, as you know, Sci is never funny on Mondays. She is only funny on Fridays. Should you ever find Sci funny on any other day of the week, you are delusional.
But now I have the paper, and I’d like to talk about anogenital distance. Anogenital distance is the distance between a man’s penis (or a woman’s vagina) and the anus. Otherwise known as the taint (‘taint anus, ‘taint balls). You might not thing this has a lot to do with your everyday lives, but Sci can assure you it can have a dramatic effect. In my particular case, Sci spent some time in charge of a breeding colony of rodents at one point in her career. I spent a lot of time weaning new rodent pups, which involved separating them into cages segregated by sex (don’t want too much brother/sister love, if you know what I mean). And so I spent a lot of time sexing baby rodents.
And baby rodents are TOUGH. You can’t just look at a baby mouse or rat and say “oh that is OBVIOUSLY a girl”.
(There’s a certain lack of expressed gender differences and societally imposed ones, is what I’m saying. Used under creative commons license, source)
So in order to sex rats and mice, you have to check the anogenital distance. In rodents, the measure of a taint is indeed the measure of manhood. If the distance is close: girl. If it’s far: boy. Pretty simple, but we all get fooled at least once.
But I thought that was just a rodent measure, I didn’t think this went to other species who have things like obvious penises or vaginas at birth (usually). But it’s got of an effect than you might think, and it’s not just boy or girl, it’s FERTILITY.
Men, let’s measure your taints.
Mendiola et al. “Shorter anogenitcal distance predicts poorer semen quality in young
men in Rochester, NY”. Environmental Health Perspectives, 2011.
So I mentioned above that the taint distance is usually used to sex rodents. This is because the length of the taint is VERY sensitive to, and highly correlated with, androgen exposure (those hormones that control secondary sex characteristics and fertility). And not only does it show androgen exposure, it’s a good predictor of how well a male will do spreadin’ his seed later in life. Male rodents with short taints show more compromised reproductive function than those with longer. But the authors of this study wanted to know whether these effects seen in rodents had anything to do with humans as well.
I can just see the authors trying to recruit people for this study “Hi, so, you’re here for the prostate exam? Great! Once you’ve turned your head and coughed, do you mind if I take this tape measure and…great. Now, if you could just take this cup, and go into the bathroom, we’ve got some Playboys in there and…hey! Where are you going!?! It’s for SCIENCE!!!”
Anyway, they somehow got a group of young men (I do mean young, they required them to be born after 1987, so everyone was 23 or younger). They got them to masturbate into a cup (and report how long it had been since they last got off, that has a real effect on semen quantity and quality). And they measured the taint, either from the base of the penis to the center of anus, or from the base of the balls to the center of anus. Comfy!
So what’s a normal taint measure? About 51.3mm from the base of the scrotum. This is dependent on BMI and height, but not related to things like testicular size (BMI and height, though related to anogenital distance, were NOT correlated with fertility measures, and I kind of have to wonder how that happened). And
anogenital distance was related to sperm concentration (how much sperm in your semen), motility (how good were your swimmers), morphology (how normal looking were your swimmers), and the total sperm count. Sadly, it’s all in very boring looking tables which I’m not going to inflict on you.
In general, men with particularly short anogenital distances were much more likely to have low sperm count, bad morphology, and low sperm motility than those with longer taints.
All right guys, now that you know that…HOW many of you got out a tape measure???
Be honest, now.
The researchers note that the people in this study were REALLY white. 81% Caucasian, so this may not translate in different races and ethnicities, and it means this is probably not a worldwide average of taint (after all, look at the penis variation!). But it does show a nice correlation between short anogenital distance and a tendancy toward fertility issues.
But remember: CORRELATION IS NOT CAUSATION. What is causing those fertility issues? Could a short anogenitcal distance be responsible for maybe putting the testicles further back, resulting in a heat increase which is known to affect fertility? Could a shorter anogenital distance mean lower circulating levels of androgens during development? Is it a genetic issue? Is it environmental exposure to estrogens? Is it getting hit a lot in the nuts as a child? We don’t know. But it certainly bears further study, especially since many people are worried about the effects of environmental estrogens on things like fertility.
And in the meantime, ladies, if you think you’re ready for kids, and want to check out a prospective mate? Grab a tape measure, and tell him to bend over and spread ‘em. Just in case.
Mendiola J, Stahlhut RW, Jørgensen N, Liu F, & Swan SH (2011). Shorter Anogenital Distance Predicts Poorer Semen Quality in Young Men in Rochester, New York. Environmental health perspectives PMID: 21377950
Looks like I need to update my lecture on anthropometry.
Spelling mistake:
"You might not thing this has a lot to do "
--merely distracting ^_^
No tape measure at hand sadly.. briefly considered using my laser Distometer but its not very good over the short stretches
Hm, I have visions of dudes in stirrups a la a pap exam. Please tell me this is how they measured.
As far as I can tell, yup that's how they did it.
Men lying on the table with legs spread at 45 degrees...sounds about right!
There is justice in the world.
Chalk that one up with benign prostatic hypertrophy vs. the reduced bladder capacity of pregnancy: Nature balancing the scales for the fact that guys don't get pregnant. (I mentioned that at my HS 40th. All of the ladies thought it was a hoot, for some reason the guys didn't.)
This really made my day! What am I saying : my week !
Considering that we know mothers provide more anogenital stimulation to males in rats, ferrets and gerbils [1] and that this has consequences on physiological development and behavior [2] (female pups artificially stimulated adopt more male oriented behaviors, for example mounting other females), probably partly by influencing the development of the corpus callosum [3], adding to this that it is even present in primates [4], I've always wondered if there were similar effects in humans. I've only done a really superficial research about this so I don't really have an answer. If the length of the taint was correlated (this does not seem impossible) with anogenital licking in many mammals, what would play this role in humans ?
[1]
Baum, M. J., Bressler, S. C., Daum, M. C., Veiga, C. A., & McNamee, C. S. (1996). Ferret mothers provide more anogenital licking to male offspring: Possible contribution to psychosexual differentiation. Physiology & Behavior, 60(2), 353-359. doi:10.1016/S0031-9384(96)80004-7
[2]
Moore, C. L., Dou, H., & Juraska, J. M. (1992). Maternal stimulation affects the number of motor neurons in a sexually dimorphic nucleus of the lumbar spinal cord. Brain Research, 572(1-2), 52-56. doi:10.1016/0006-8993(92)90449-
[3]
Rogers, L. J. (2001). Sexing the brain. Columbia Univ Pr.
[4]
Kaplan, G., & Rogers, L. J. (1999). Parental care in marmosets (Callithrix jacchus jacchus): Development and effect of anogenital licking on exploration. Journal of Comparative Psychology, 113(3), 269-276. doi:10.1037/0735-7036.113.3.269 )
Awesome, thanks for covering this! This is actually a measurement of student of mine may end up doing on marmosets
.
I briefly saw this pop up in my blog feed, but glazed over it because I was busy. Glad that you brought it back for Friday. =)
Within height groups, usually a higher percentage of a man's genital structures are inside his torso when his 'taint' is longer than his equally tall comrades. This affects the temperature and protection of various essential parts, and may very well have other consequences.
There is a lot of variation in how much of a man's penis and associated bits are internal vs external and just covered by thin tissue and skin. A lot of men who seem to have longer than average penises actually just have a smaller than average percentage of the total length inside - the differences in total length are smaller than the differences in external length.
From self reporting, it can be more fun to have more bits close to or poking out of the body's surface (the easier it is to affect a prostate, for example, the more pleasure it's owner can be subjected to), so it's interesting that fertility is higher when more bits are inside. If I was an evolutionary biologist I would, I'm sure, come to some quite provocative conclusions about how this came about - but I'm just an ordinary guy, so I think it's probably a non-selected-for accidental human variation.
[...] methodology was slightly different, and since there was some question regarding methodology in the comments on that post, I figure we'd go into the methodology a bit here. In this study, eligible patients were recruited [...]
[...] methodology was slightly different, and since there was some question regarding methodology in the comments on that post, I figure we’d go into the methodology a bit here. In this study, eligible patients were [...]