hi! this could be more a question for /r/AskAnthropology (so do run a search over there - I'm sure I've seen it come up over there), but there have been posts on the subject here, so check these out

• At what point in history did humans begin to understand that sex causes pregnancy?

• When did we figure out that sex leads to pregnancy?

• How long have we know how conception works?

more on alternative theories

• [Serious] How did people view conception in pre scientific times? What was their view of semen, menstruation etc.? How much did they know?

• Has there ever been a culture that has believed that pregnancy happens for a reason unrelated to sex?

• Was there ever a time in history when humans didn't know that sex led to pregnancy?