Excerpt from a book.
So why do men (and women) masturbate?
We’re not actually sure. There are no well-established, proven theories about the evolutionary functions of male masturbation (probably because no scientist wants to be known as Dr. Jerk-Off). But there are a handful of hypotheses:
One is a learning function. Masturbation teaches you quite a bit about your penis, how to use it, and some basic sexual skills. Masturbation and various forms of mutual masturbation are used by many animals in this way.
Second is sexual release. Men, especially young men, are biologically designed to have far more mating desire than they have opportunities to fulfill it. Masturbation is a way to release some of this energy in a safe, appropriate way—to reduce sexual frustration and make it possible to show more patience and strategic self-control in mating.
The third is a reproductive function. Your sperm are constantly being made and have a relatively short lifespan (about 5–7 days, usually). Once it’s been in there past that time and loses its motility (its ability to reproduce), it is basically useless. So you have to get rid of it to make way for new, living sperm that is reproductively useful. Masturbation is a way to “clear the pipes” and replace the old with the new.
The fourth theory—and this is far more speculative—has to do with sexual imprinting and fantasy. Teenage masturbation could help with learning which female traits to consider romantically attractive, by associating them with sexual pleasure.
A final possible function of masturbation becomes more relevant later, after sexual maturity, as a way to help to preserve monogamy. Even if you are in a committed, mutually fulfilling relationship, men can and do have lust that makes it tempting to cheat, or mate-switch, or abandon our mate for greener pastures. Generally, this would be a stupid idea, especially if you start having kids with your mate, because your reproductive success is probably highest if you stay with her and invest in the offspring. So along came adult male sexual fantasy and masturbation as a possible solution
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Source: #mental-masturbators .