So that's why it's called a boner!
The baculum, or the bone that holds up an erect johnson, is prevalent throughout mammals, but it’s clearly absent in humans. Why would that be? Well, the amount of partners that a species typically has may just have something to do with it. Humans may get it on more than some other species, but we try to have just one partner for long periods of time. And that killed the bone in their boners.
Researchers have recently concluded that human males have lost the bone that used to hold up their penis, and it’s all due to the social construct of monogamy.