Via Stacy Lynn Baum @ Flickr.
In last week’s “Savage Love” column, Dan Savage urged readers to Google “sperm competition” for some enlightenment on sex and the male psyche. Now I don’t always agree with Dan’s advice, but when he challenges me to Google something, I really can’t resist (as you might imagine, this has led to all kinds of horrifyingly icky–yet fascinating!–revelations). And I must say, what I learned seems to have all kinds of interesting implications.
Sperm competition is, simply, the race between the sperm of two or more males to fertilize an ova. And thanks to evolution, the male animal–including the male homo sapiens–has natural adaptations that maximize the chance of his sperm getting to the finish line first.
Consider this, from the magazine New Scientist:
Men who view pornographic images of two men and a woman produce better-quality sperm than men viewing pornographic images of just women, an Australian study reveals.
The finding suggests that humans may be capable of subconsciously increasing semen quality when faced with the possibility that their sperm will have to outrun those of other men in a woman’s reproductive tract.
In the study, zoologists Leigh Simmons and Sarah Kilgallon of the University of Western Australia in Perth asked 52 heterosexual men aged between 18 and 35 years to ejaculate into a container after viewing the two types of image. The volunteers had previously abstained from sexual activity for two to six days. In samples from men who viewed the images containing the two men and a woman – the “sperm-competition” images – 52% of the sperm were motile. This compared with 49% sperm motility in the men who viewed the images of women only – a difference that was statistically significant after taking into account lifestyle factors such as cigarette smoking and alcohol consumption.
Oh, there’s so much of interest here. First of all, it would appear that girl-girl porn actually reduces sperm motility! If you’re the porn industry, you probably want to bury that info as fast as possible. Secondly, it confirms that sperm competition is so hard-wired–no pun intended, I swear!–that the presence of other men during sex, even if it’s only self-sex and the other men are on a screen, gets those swimmers swimming like single-cell Michael Phelpses.
Does this explain why ex-boyfriends tend to resurface when they know you’re dating someone new? If even implied competition makes their sperm more aggressive, does the urge somehow work its way north and lodge in the brain, thus accounting for drunken phone calls and late-night emo-mails? I wonder. After the end of both my last two serious relationships, I was happily shtupping away with a new beau when my ex decided he wanted another try. The first I did not take back, the second I did, but lived to regret it. If only I’d known it was just his sperm talking…
This study was covered on the AWESOME NPR show Radiolab. They also discuss how people over time have conceptualized sperm and fertility. For example, because sperm is visible and ejects from the male body, for a long time people thought that everything to make a person was in male sperm, making women no more than an incubator. The gender relations that spring from these scientific conceptions of sperm are so fascinating.
http://www.wnyc.org/shows/radiolab/episodes/2008/11/21
I’d like to see some other studies before I buy it. The effect’s pretty small.
Anyways, the effect in us is nowhere near what other species go through for sperm competition. In one of my bio labs in college, the professor warned the men of the immasculating effect of comparing our sperm size against other species’.
Dragonflies have barbed hooks on the male organ to scrape out semen before ejaculating himself. A male coyote’s penis swells after ejaculation, lodging his member in the female until such time as it’s virtually guaranteed that his won’t be out-competed by the next guy.
It looks painful for all parties. I’m pretty sure I’d like sex a lot less if it worked like this for us.
Is 52% v. 49% statistically significant? But yeah, I think science has debunked the “women are naturally monogamous” thing. I recall some study that correlated testicle size to number of partners the female of the species tends to have, and homo sapiens came out somewhere in the middle of the slutty-chaste (big ball-little ball)spectrum.
Yes, 52% v. 49% is very statistically significant, particularly in medicine.
Spark’s right; one of the funny things I found in searching on sperm competition is that in the primate family there’s a direct evolutionary cause-and-effect between the size of the male’s junk and female monogamy. Chimp females mate promiscuously, so the males have evolved huge testicles and ejaculate huge quantities of semen in order to give them a better shot–so to speak–at fertilization. In gorilla society, though, the alpha male dominates the females so that they don’t routinely mate with other males and, not surprisingly, gorillas have relatively small testicles and quantities of ejaculate. Humans fall in the middle of the two extremes.
Thanks for the explanations, Becky. I couldn’t bring myself to google a phrase including the word “testicle” for more info. I guess I’m the opposite when it comes to Savage Love google challenges.
I read an article years ago (circa 2002) that showed supermicroscopic photos of conception. The photos revealed that the egg sends out a filament which grabs a sperm and draws it in, essentially debunking the whole “fastest swimmers” mythology because it’s all about which sperm the egg chooses to let in.
The piece talked about how this discovery was going to radically change the way we conceptualize conception. I had never heard anything like it before or since, and now really wish I had saved the article.
Wait, wait, wait, I read in a Discovery article that sperm is actually very weak stuff with no aim and it gets though the cervic mucus by working as a team (and luck) it reaches the egg which is way bigger and hooks it and drags him toward her to stop him escaping because sperm doesn’t actually burrow into the egg or anything at all, sperm is better at escaping. I suppose speed would be important, but never is the stuff I’ve written talked about.
Anyone ever read “Dr. Tatiana’s Sex Advice to All Creation” ? If you’re interested in this type of thing, it’s an awesome read
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