I've recently read the "Sperm wars" book by Robert Baker. It deals with human sexuality and infidelity. The main premise of the book is that human male has different kinds of sperm:
- Regular sperm for fertilization
- Toxic sperm that kill competitor sperm (similar in concept to white blood cells)
- Slow, inactive sperm to block channels in female cervical filter
According to the author, when a female engages in infidelity or group sex, the sperm actually "goes to war" killing competition and preventing passage through cervical filter.
Are there are indeed different kinds of functional sperm in humans, and are their functions involved in sperm competition / warfare? In other words, does human sperm not only fertilize the egg, but also to block passage of competitor sperm and even kill it?