One reason humans are special and unique: We masturbate. A lot.

Sometimes, the title of a story I'm linking to just speaks for itself.

Interesting fact from the text, as pointed out by Richard Metzger:

Amongst the more interesting things discussed in the article–trust me, it's a great read–is the fact that most men basically need to spill their seed, drain the vein, etc, at minimum, every 72 hours. Pair that notion with studies that found women's bodies rejected sperm that had overstayed its welcome in the male testes (had not been flushed out) by 48 hours.