As Iosif Alexandrovich wrote: "Why is the whole virgin, since there is a knee."
I fundamentally disagree. Some ladies spread their legs in front of me, and think that I will immediately get up. Nonsense. There is no ardor, passion. Even prostitutes - normal and more expensive - do not just provide their bosom for the act. And they play and turn you on. Yes, and a woman in lingerie is more exciting, because a secret that you want to look behind.
Excite rather only men. Because men "love with their eyes", and what kind of genitals they love depend on them) There is indeed a theory that there is an additional gland in the infra-eyeball - secreting additional hormones. This no longer applies to artists, because they draw a lot of nude, and from youth learn to abstract, otherwise one of Bames's anatomy will "excite" you on every page.) In reality, it is not the appearance but the state of a person that excites - it is transmitted.
Arousal is the preparation of the body for sex. As soon as your brain receives a signal that intercourse is near, it begins to prepare the body for this. The blood should flow to the right places, the ladies should get grease, etc. In men, this preparation starts on average sharper and proceeds faster. Guys most often can "plant from the doorway" without problems. In women, this is usually a more extended process in time - the peak of arousal, which means that full readiness begins in about half an hour.
There are many different things that can trigger your brain to start preparing. There are common for everyone, and there are individual ones. For example, as a child, you might see an older brother having fun with a girl, and she is wearing a yellow bra. The scene could impress you with something, and from everything you see, you will remember a bright bra. And your brain will write the formula "sex = yellow" in the subcortex. You may not even be aware of this, but Yandex for some reason will cause warm feelings in the lower abdomen. I am exaggerating and primitivizing, of course. But in general it works like this. This is how we have individual arousal triggers.
And there are triggers common to everyone for obvious reasons. And the sight of the genitals is one of them. The sight of the penis clearly tells the female brain that the likelihood of early sex is high. So we need to start preparing. And the woman starts to get excited. If he is already standing, then everything will happen very soon and you need to prepare more quickly. And the excitement rolls on more, the preparation process is faster. While a bare hand or bare ear does not carry such information. Few people think: "This dude took off his glove - he probably wants to get hold of me right now." Only if nothing special and intimate about hands has happened in your life that would convince your brain that the naked finger is a sure sign of impending sex.
We are not necessarily turned on by what is hidden. We rarely see other people's heels - but they excite few people. For this to happen, something has to happen to allow the brain to remember heel = sex. For example, someone can choose for the first sex a position when the girl's legs are thrown over her shoulders, during orgasm, turn her head and see her heels. The brain will mistakenly associate the peak of pleasure with the appearance of the heels (the brain generally loves to look for patterns in everything and remember them), and now you are a fetishist. But this will be your individual trigger for arousal. And the genitals are the trigger for everyone. And do not confuse cause and effect - it is customary to hide them with clothes, because they excite (that is, they are objectively associated with sex for everyone), and do not excite, because they are hidden. At least initially. And then there is the effect of a snowball. We are accustomed to the fact that everything sexual is hidden, so we often sexualize everything hidden. Therefore, the fact that it is customary to hide sexual objects makes them even sexier. But this is not the root cause.
I think it's all about associations. Thoughts of possible actions appear on their own. Not only for pleasure, but also for procreation
Excite not specifically the genitals, but the fact that they are hidden. Surely you have heard about a fetish on women's feet, Quentin Tarantino is an open fetishist on this issue. So this part of the body, which cannot be seen in ordinary life - they are always hidden under shoes or socks, but nevertheless, some are insanely excited at the sight of barefoot girls. Sexuality arises from curiosity about someone else's body. And at the same time, it disappears when partners go naked around the house or often shower together. Excitement requires intrigue and distance. After all, a girl in a short skirt looks much sexier than completely naked, right?