This piece describes some interesting new research that at least raises the possibility that semen plays a triggering role in ovulation (or some other supporting role in preparing for pregnancy) in humans. I found this passage unintentionally amusing (with emphasis added):
Mammals can be divided into two groups, Adams said: Induced ovulators and spontaneous ovulators. Spontaneous ovulators are those with a regular menstrual cycle, such as humans. These mammals release egg cells on a regular schedule, whether they've copulated recently or not. . . .
Spontaneous ovulators include animals such as camels and llamas that only release eggs in response to sex.
Researchers long assumed that it was the sex itself that induced this ovulation, Adams said. The stimulation of the vagina or some mix of pheromones was assumed to be the culprit. But in 2005, Adams and his colleagues discovered a protein called ovulation-inducing factor in the seminal fluid of llamas and camels. This protein did exactly what its name would suggest, inducing ovulation in females exposed to it.
Why culprit and not "cause," Dr. Freud?