How Did Our Ancestors Know How To Have Sex?

I don't think they knew to have sex. I personally think that it all occured by experiment of the body and what it does. People continued to do it because of the pleasurable feeling they got from it and it turned out to what it is today - the reproduction of humans

Great question...Well probably the same way we know how..Spin the bottle!
Haha..just teasing.
 
Probably exploring there bodies and then exploring each others and maybe getting some ideas from watching the animals...

Very good question. I've always wondered this. I guess its just instincts and etc etc....  
Maybe God showed them how :L
Jokes... X

it would've all began with Adam and Eve- sex is a God given gift- with His rules of course.  Anyway- it just comes natural.  Do you know why Adam called Eve- woman!  When he first saw her he said " woh- man!"  lol a joke!

Originally, its instinctive....
    and secondly... The parts fit.... Haha j/k

I think they probably got the idea on what to do from watching the animals, but I also think that we are born with the natural desire to be intimate with the opposite sex. Great question though!

I'm not sure about women, but us men can figure it out. We have little choice.

Well as you know a man and woman have different things and they probably put 2 and 2 together and that's were there fun started. Common no one could live without sex

Instinct and the need to continue the species

they swa animal and figured it out

after a while figured out that the activity produced a baby