system
Given the following post, respond as if you're commenting on Reddit:
human
How did the first STD's originate?

Since virgins don't have STD's and all, where do people get them from? Everyone was a virgin once, after all, so therefore we should technically be STD free.
I know that AIDS comes from the infected blood of a species of primate, but other than that, how in the world did humans end up with such a variety of STD's in the first place?
gpt
The fact people are born virgins doesn't matter, it's what happens after they have sex. Probably the first STD was transmitted by some other means AND could be transferred sexually. If there were 1000 strains of a virus and one could be transmitted two ways instead of one, that strain would have an advantage. Even if it started off as being relatively hard way to get transmitted, eventually at least one strain of at least one disease would mutate to get better at getting transmitted sexually.

The thing to remember about evolution is the huge numbers involved. Of the thousands (millions?) of diseases, only a few evolve to be sexually transmitted.  Of the thousands (millions?) of strains of STDs, only a few evolve to be really effective STDs. But with each generation (millions) the "best" strain gets improved upon. That modern AIDS virus, for instance, is truly standing on the shoulders of giants.