Tuesday, January 09, 2007

Removing the Helmet

Whilst I was reading around for ideas for my previous posting on sex, I came across an interesting paper, which discusses some evolutionary theories about the penis. Specifically, I found the discussion regarding the existence of foreskin to be quite entertaining. A couple of extracts:

Another intriguing implication of the difference between circumcised and intact males is the question of self-cuckoldry. Put another way, is it possible (short of artificial insemination) for a women to become pregnant by a man she never had sex with? We think the answer is “yes.” If an uncircumcised man (Male B) were to have sex with a women (Female A) who recently had sex with another man (Male A), in the process of thrusting his penis back and forth in her vagina some of Male A’s semen would be forced under Male B’s frenulum, collect behind his coronal ridge, and be displaced from the area proximate to the cervix. After Male B ejaculates and substitutes his semen for that of the other male, as he withdraws from the vagina some of Male A’s semen will still be present on the shaft of his penis and behind his coronal ridge.

As his erection subsides the glands penis will withdraw under the foreskin, raising the possibility that some of Male A’s semen could be captured underneath the foreskin and behind the coronal ridge in the process. Were Male B to then have sex with Female B several hours later, it is possible that some of the displaced semen from Male A would still be present under his foreskin and thus may be unwittingly transmitted to Female B who, in turn, could then be impregnated by Male A’s sperm. Were Male B circumcised, this would be a far less likely outcome because the residual foreign sperm on his penis would not be afforded the protection by the foreskin from desiccation, light, and cooling and would likely perish during the interim separating sexual encounters with different partners.
If the foreskin makes the human penis a vector for fertilization by proxy, why is the foreskin still there? We assume that during human evolutionary history the incidence of self-cuckoldry was not high enough to offset either the advantages of semen displacement or the advantages of the foreskin, which affords protection of the glans.
Is part of the reason that some religions dictate circumcision (if you pardon the pun) to stop men impregnating women with sperm from other men? It's an interesting idea, although I can imagine other reasons as well. It is known women who's partners do not have foreskin, are less likely to get cervical cancer, due to the presence of the human papilloma virus, which can live under a male's foreskin. Perhaps the religious practice came as a consequence of discovering this benefit, or perhaps it is a combination of these ideas and more.

Trying to work out why the bits of us do what they do, highlights the importance of evolution on our very being. Do you really think an omnipotent god would have designed these things on purpose?