The sperm that fail to make it up a fallopian tube might not simply “lose their way,” it turns out. No, some of them could be “kamikaze sperm”— specifically intended to attack other men’s sperm, and to prevent them from fertilizing an egg.
The theory is still up for debate, but clinical sexologist Dr. Lindsey Doe tells the Daily Mail that up to 40 percent of the sperm in male ejaculate may not even be designed to inseminate an egg. Instead, the tricky fighter sperm create traps by weaving their tails together to build walls and barricades! Evolution, right?
Dr. Doe also claims that men who suspect their partners of being non-monogamous produce more fighter sperm. The effects are sort of self-defeating, though, since more fighter sperm means fewer sperm to actually inseminate the egg. So even if it is real, not a totally foolproof evolutionary strategy.