It's not about the number of partners, but the size of the pool. Diseases spread via contact. If 500 women have 10 partners from the pool of 500 men in a villag

It's not about the number of partners, but the size of the pool. Diseases spread via contact. If 500 women have 10 partners from the pool of 500 men in a village, chances of spreading e.g. gonorrhea are smaller than when 500k women when 10 partners from a pool of 500k men in a city. And I'm relatively sure that in smaller communities there's less chance of anonymous sex: the social control, lower frequency of encounters. Imagine the opposite: 1000 years ago, AIDS and gonorrhea spreading all over the world at current rates (88 million cases of gonorrhea per year) without any medication or protection. That would have ravaged the population, or made us immune, but neither happened.