Hi Khayah, yes this is one of those fascinating ones which at first glance makes you think, really. But it is a well-documented phenomenon, if you simply Google “is testosterone in our saliva”, and “why do we kiss” you will find countless reports of this phenomenon. I believe the theory is the main reason we started kissing is most probably linked to the desire to pass on testosterone to bring about arousal. It is postulated that the reason men like sloppy kissing more is that the more sloppy the kiss, the more testosterone gets passed on, because women have a lower level of testosterone, small amounts can have a big influence when it comes to increasing sex drive.

You may find these links of interest, just from a quick Google search:

https://www.wired.com/2009/02/kissingscience/amp

A quote from the piece: “There’s evidence that saliva has testosterone in it, and there’s also evidence that men like sloppier kisses with more open mouth,” Fisher said. “That suggests to me that they are unconsciously trying to transfer testosterone to trigger the sex drive in women.”

https://www.healthline.com/health/benefits-of-kissing

A quote from the piece: Romantic kissing leads to sexual arousal and is often the driving force behind a woman’s decision to have sex with someone. Saliva also contains testosterone — a sex hormone that plays a role in sexual arousal. The longer and more passionately you kiss, the more testosterone gets released.

If you do some googling, you will find many more details on this subject. Of note, it is widely postulated that one of the reasons women evolve to be so selected with kissing is due to its power to increase the sex drive in women through the increase in testosterone.

So it’s possible that the reason women have evolved to use kissing as a means of sexual selection is that men worked out that kissing has the power to lead to sex, so women have evolved to utilise kissing as a means of identifying immediately whether they should keep kissing or not i.e. to counter the male discovery.

Of course these are all theories, we will ever know for certain the roots of it. But it’s well documented that testosterone is in saliva and that a large part of why we have evolved to kiss is due to the power of testosterone to increase the desire of sex in women a.k.a. bring her to arousal.

Thanks again for reading! Much appreciated :-)