The ancestor of the European milch cow was the ox-like wild aurochs, which finally went extinct in the 17th century. The aurochs could be fierce and stubborn, but a few centuries of breeding transformed it into an animal so docile it will actually line up to be milked and so prolific that a single cow produces around 100 pounds of milk a day.
The cow's genome, for whatever reason, responded readily to human dabbling. In this, cows are like wolves, from which we've created dog breeds as different as Chihuahuas and Great Danes, and unlike cats, which all look and act pretty much the same despite having been domesticated back in the Neolithic era. Given its genetic pliability, it was probably inevitable that the cow would become a major dairy animal wherever it could survive.
In America, cows never had any real competition. The Ice Age had scoured the continent of all of its large ruminants, with the exception of the bison, and Native Americans had no dairy tradition for the colonists to adopt. So, as Deborah Valenze recounts in "Milk," Europeans brought cows along with them when they set off for North America and then let these autonomous food factories graze on the continent's unlimited vegetation until their milk or meat was needed.
The cows thrived, to say the least: Between 1627 and 1629, while the colonists were fretting about other things, the number of cattle in Virginia grew from 2,000 to 5,000.
The iron fist of cow-milk hegemony isn't just thanks to cows' high output and doziness. Cow's milk has some real aesthetic and practical advantages: It separates itself into cream and milk, so it can be made into an easily drinkable beverage as well as all the luscious cream-based comestibles, such as ice cream and crème fraiche. Its fat content is similar to that of human milk, which makes it familiar to our palates, and its relative blandness makes it an attractive blank slate for the creation of cheeses with a range of flavor profiles and consistencies, from runny Camemberts to rock-hard Goudas.