It’s hard to believe that people didn’t realize that if two big cows had a baby that baby would grow up to be bigger.
One possibility is that the scale of farming was so small that people couldn’t notice lineages. If you only ever interact with one or two cows it’s hard to notice their kid picking up their traits. And then it’s hard to see which chickens are breeding with other chickens.
Another possibility is that there was actually a cultural shift just about systematically documenting things in the world. This is suggested by Against the Gods.
Another Idea behind its time - ToA