Why were they even trying to drink milk if it upset their stomachs? That’s not a great mystery. In the parts of the Near East and Central Asia where people first domesticated goats/sheep/cattle, the animals’ reproductive schedules were nothing like the year-round system we have today. They gave birth and came into milk as the weather was warming up. When they reached peak production, local daytime temperatures could easily reach more than 100 degrees F (40-plus C) and milk could go sour within a few hours of milking. So the precursors of yogurt could have almost invented themselves.