Original post by tazarooni89From a biological and evolutionary standpoint, it is advantageous for men to have sex with as many women as possible, disperse their seed as far and wide as possible, thereby increasing the likelihood of producing a lot of offspring. The more attempts at procreation they have (particularly, but not exclusively with females displaying signs of high fertility), the more healthy offspring they are likely to produce. It is also advantageous for them to value women who are not sexually promiscuous, because otherwise they are competing with many other males in the race to be the one who actually gets her pregnant.
On the other hand, for women it is not particularly advantageous to have sex with as many different men as possible. Unlike a man who can theoretically have as many women as he wants carrying his children all at once, a woman only has one uterus, with a very limited capacity for the number of different men's children it can house. Unlike men, who produce millions of sperm every day, even into their old age, a woman's reproductive system is very limited in the number of children it can produce, and it stops working around the age of 40-50. It is therefore more advantageous for them to value virile men who are likely to produce the most healthy offspring, and to restrict their sexual activity to select men of the "highest quality" they can get, so as to give their few attempts at procreation the highest chances of being successful, rather than waste them on any old person. It's also advantageous with them to be in a relationship with a male who looks like he's going to stay around and help provide for, and protect her offspring, giving it the highest chance of survival.
The "key and the lock" analogy does not need to be solely about the physical resemblance to anybody's anatomy, which is purely coincidental. You could just as easily think of it as a combination safe, and the code used to open it. Or an exclusive club with a guest list, and a swarm of people trying to get in, most of whose names are not on the list.
The point of the analogy is that, the lock is protecting something rare or valuable from being accessed by anyone other than a select few; just as women are instinctively predisposed to do, with their few chances at procreation. There's supposed to be a filtering mechanism in place to make sure only the "right" people get through. But it's not a great filtering mechanism if it can be bypassed by just anybody. Whereas the purpose of a key is to allow the holder to gain access to these rare and valuable things. The most useful key is the one that opens the lock that is guarding the most valuable stuff. But on top of that, the key is even more useful if it is able to open more locks than just that; just as men are predisposed to want to mate with, not only the highest quality females, but also a high quantity of females.
These predispositions carry over into society today, where men are thought to be "successful" in having sex with many women, because it's a sign of being a "high quality" male that so many women are willing to have sex with him, and consider him adequate enough to spend one of their precious attempts at procreation on him. He's also perceived to have got something that he wanted, but was difficult to achieve.
On the other hand, women who are promiscuous are seen as "unsuccessful". It is assumed that they want to get a man's commitment, but are unable to do so, and therefore end up with different partners all the time, which is a sign of a "low quality" woman. The trait of having had multiple sexual partners is also less valued by their potential suitors.