@NecessaryScene
I'm wondering if you're retrofitting a more advanced "genetic sex" definition in place of the more fundamental one to say they had a "one sex model", when obviously they'd always have known you needed one of each sex.
They just didn't know why.
They didn't always know. There's a plausible hypothesis of the creation of the patriarchy, which posits that the agrarian revolution, and more specifically the knowledge about reproduction gained from early animal husbandry, led to creation of the patriarchy. Until then, the general way of thinking was that men had nothing to contribute to reproduction.
So about 12,000 years or so ago, the general idea was that women had this miraculous power to make new lives. And the life was put into the woman by whatever spirits her tribe believed in.
During the transition from a nomadic to a settled lifestyle, animal husbandry became of great interest to the people of the time. They started breeding animals, at first just to increase their livestock and later to improve the livestock.
Inquiring minds of the time soon noticed that soon after that peculiar-coloured bull had mated with the brown cow, it bore a peculiar-coloured calf.
Didn't take very long for those early agrarians to understand that male animals and male humans had a role to play in reproduction after all. And not only that, if they wanted to make sure their offspring had the best chances, they kept a close eye on their females.
And that was the beginning of the patriarchy according to that hypothesis.
Of course they held onto their one-sex model of reproduction. Instead of thinking of women as life-giving, that was now the man's role. The woman, as previous posters have already said, was now recast as a mere vessel. She made no contribution to the child other than providing a growing environment.
And the man who wanted to ensure his offspring had the best chances, exerted control over the woman he was mating with.
(It's entirely plausible that keen observers of the natural world realised the connection between mating and offspring long before the agrarian revolution. But there was no societal forces coming into play before people were settled, so any early knowledge didn't have widespread consequences.)