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Did cultural evolution create sexual purity taboos to prevent the spread of STIs? A few weeks ago, I wrote a post assuming this was obviously true; after getting some pushback, so I want to look into it in more depth.

STIs were a bigger problem in the past than most people think. Things got especially bad after the rise of syphilis: British studies find an urban syphilis rate of 8-10% from\\xa0the 1700s\\xa0to\\xa0the early 1900s. At the time the condition was incurable, and progressed to insanity and death in about a quarter of patients. If you\\u2019ve got a 10% local syphilis rate, you are going to want some\\xa0major\\xa0sexual purity taboos. It\\u2019s less clear how bad they were in truly ancient times, but given how easily the extent of syphilis has slipped out of our cultural memory, I\\u2019m not ruling out \\u201cpretty bad\\u201d.

Here are some things I think of as basic parts of sexual purity taboos. All of these are cross-cultural \\u2013 which isn\\u2019t to say they\\u2019re in every culture, or that some cultures aren\\u2019t exactly the opposite, just to say that they seem to pop up pretty often. I\\u2019m writing this from the male perspective because most of the cultures I know about thought that way:

1. If your wife has sex with another man, you should be angry
2. Preferably you should marry a virgin. If you think your bride is a virgin, but she isn\\u2019t, you should be angry
3. If you\\u2019ve got to marry a non-virgin, then marrying a widow is okay, but marrying a former prostitute or somebody known for sleeping around a\\xa0lot\\xa0is beyond the pale.

All of these are plausible ways to prevent the spread of STIs. If your wife has sex with another man, she could catch his STI and give it to you. If your bride isn\\u2019t a virgin, she might have STIs. If someone\\u2019s a widow, they probably slept with one known person whose STI status can be guessed at; if they\\u2019re a prostitute or slept around, they slept with many unknown people and have a higher chance of having STIs.