Phrased differently - How (and when) did people figure out that children inherited traits from both mother and father? Also, were there any cultures that did not have the concept of paternity?
This would date to prehistorical times. Goats and cattle were domesticated ~10,000 years ago. Domestication consists of selective breeding, which can't be done without the knowledge that sex leads to pregnancy and that physical traits of the parents can be transmitted to the offspring.
And for a fact, I don't believe that this was suddenly discovered 10,000 years ago. I think humans have known about these things for many tens of thousands of years. People who live close to the natural world and depend for their sustenance directly on it tend to learn these things pretty quickly.