How did sex work back when we were cavemen?

i don't mean HOW did people have sex, I mean how did cavemen decide who they had sex with. I'm talking about back when reproducing was really important, like when the infant mortality rate was about 20%, cause I've heard that back then people didn't live very long. but did women only have sex with the strongest guys? and how did the men convince the woman to sleep with him? and would the man move on to the next woman once he got the last one pregnant? like if a guy saw a woman who wasn't pregnant, would he automatically go over to her and have sex with her? and did they only have sex with people in their own age group? or were there 16 years old guys and 30 year old women having sex together, who were both in their sexual primes?
How did sex work back when we were cavemen?
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