This makes me think about how cows are probably the largest domestic mammal humans have so are ideal for milk producers. Camelids (camels, llama, alpaca) and goats are also good sources of milk used in the world where cows aren't really feasible. There are larger mammals but they lack the traits of an organism that can be domesticated easily if at all. Elephants for example are difficult to breed, feed and, lead.
Anyway I am trying to say that milk from cows has probably helped humans a lot. When we started learning to cook and farm our jaws shrank and our brains grew.