It's a wonder to think that so many centuries ago our ancestors were able to finally domesticate cows. They then began to milk the cows and realized what good nourishment this food gave them.
But the one big problem was that it didn't stay fresh for very long. Probably, by accident they discovered that fermented milk was a tasty thing and it lasted quite a while. This idea spread over the populated world. Almost every culture has fermented milk products that they still use today.