More specifically, a protien in semen penetrates the blood brain barrier and enters women’s brains, causing the hypothalamus and pituitary gland to release the hormones required for pregnancy. Apparently, semen causes women to ovulate.
Researchers have found that this protien exists in animals all over the world. Chinese researchers actually discovered the finding in 1985, but because it was so counter-intuitive to common knowledge at the time, scientists simply ignored it!
In 2005 a new group of researchers verified what had already been known for two decades by injecting semen into the leg of female llamas, part of a group of animals that only release eggs in response to sex.