There are two hormones play an important role in ovulation:
- Follicle Stimulating Hormah (FSH): this hormone causes an egg in the ovary to ripen and mature
- Luteinizing Hormone (LH): this hormone triggers ovulation and release of that egg.
Curiously enough, these two distinctively female hormones are actually found in semen. Why? This snippet from Scientific American explains it very well:
Unlike females of other primate species, women do not have breeding patterns governed by season or standardized cycles, and there are no obvious signals—such as a fire-engine red, swollen rear end—giving away their time of the month. So for a naïve human male, impregnating a woman as a consequence of sexual intercourse is much more a roll of the dice than it is for males of other species in their mating behaviors. Just as with any other species, though, getting the timing right so that release of semen coincides with the release of eggs is key. As a counterdefense against women’s concealed ovulation, male evolution had a trick up its sleeve, which was the ability to manipulate the timing of a woman’s ovulation to suit his own insemination schedule—that is to say, semen chemistry seems to give premature eggs a nice little nudging. Hence the conspicuous presence of FSH…and LH.
So what does this have to do with sperm competition? Well, the higher the levels of FSH and LH in a woman’s body, the more likely that woman is to enter ovulation. A woman will therefore be exposed to higher levels of FSH and LH the more semen that is ejaculated into her. And as we just said, the higher the levels of FSH and LH, the more likely she is to enter ovulation. Ipso facto, it stands to follow that sperm competition can induce ovulation. Pretty interesting stuff, isn’t it?