Geeking Out About Sex

I really like it when people publish interesting science articles about sex. As much as we think we know about it, there’s always something new to learn. So put your sex geek hat on!


First, back in 1999, BMJ.com (originally the British Medical Journal) posted an article showing an MRI scan of penis-vagina intercourse. Up until then, we had drawings like the one to the left, which comes from Dickinson’s amazing book Human Sex Anatomy: A Topographical Hand Atlas, which I consider a must-read for anyone who wants to be a sex nerd. (As is Netter’s Reproductive System, btw.) You can click on the picture for a larger image.


While these drawings are really useful, they’re still based on one person’s understanding of anatomy, as well as their artistic skill. So I’m geeking out on the MRI scan shown to the left. Click on it to see a larger version, along with a chart showing some of the organs that are a bit hard to identify. Maybe it’s just me, but I think it’s fascinating. Plus, as the authors of the article discuss, it shows that the root of the penis goes much further into the body than most people realize. They also correct some of the information that sexologists had previously accepted. For example, it looks like the uterus doesn’t actually increase in size during arousal. Let’s hear it for the advance
of science! (Of course, we need replication of this work to fully validate it, but it’s still cool.)

In other sex geekery, an article in Evolutionary Psychology (pdf available here) examined the evolutionary purpose of the scrotum. We’ve long understood that past of the function is to keep the testicles at a lower temperature than the body cavity in order to maximize sperm production. But there are some amazing adaptations that are part of that, and I admit that much of this info is new to me.

First, one possible explanation for why one testicle usually hangs lower than the other is that “with one testicle suspended slightly above (or below) the other, there is a corresponding increase in the available surface area subject to heat dissipation and cooling.” Scrotum asymmetry as an evolutionary advantage!

I’m intrigued by the notion that part of why the testicles tend to pull up close to the body before ejaculation is in order to warm the sperm up and get them swimming. The same mechanism serves to protect the testicles during sex. (The authors note that fear triggers the same reflex, perhaps in order to avoid damage when in danger.)

It’s also really interesting that, as part of the temperature regulation functions of the scrotum, the arteries that supply blood to the scrotum are next to the veins that take blood away. That means that the cooler venous blood lowers the temperature of the blood entering the scrotum in a rather efficient heat exchange. Amazing!

This sort of research is really helpful to me as a sex educator. I rely on scientists like these folks to do this work so I can make sure that I’m offering accurate information. Even if you don’t geek out on it yourself, thank a scientist the next time you meet one. Without them, we wouldn’t know as much as we do.

2 Responses so far.

  1. Dave says:

    Love this “geek out” article and I hope you continue it as a series of articles like this.

    So true about the differences between the artist’s concept vs. the MRI.

    The artist’s illustration would have you believe the penis has no “bulb” or “root” of much substance past below the pubic bone towards the tail bone. The MRI shows a substantial portion of the penis is internal.

    What was surprising to me more was the position of the uterus. The MRI image guidance has the uterus below the vaginal canal instead of above, as is typical in most medical anatomy texts.

  2. Joan Price says:

    Have you read Bonk by Mary Roach? It’s a fascinating (and very entertaining) book about sex research — how they do it, who does it, what they learn. I loved it. I reviewed it on my blog:
    http://betterthanieverexpected.blogspot.com/2008/11/bonk-by-mary-roach-book-review.html

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