Let's start at the beginning: cows were actually domesticated more than once! The result is that modern cows can be divided into three genetically identifiable subspecies: taurine cattle in Europe and Western Asia, indicine cattle in East and Southeast Asia, and sanga cattle in Africa.

Indicine cattle were domesticated in what is now western India from the now-extinct Indian Auroch about 6,000BCE. Mapping of their Y chromosome (male line) suggests that bulls from this population were introduced to northeastern Africa about 1000BCE via the Levant, which is consistent with the appearance of cattle in Egyptian art. The resulting African population shares mitochondrial (female line) DNA with taurine cattle, but also shows good deal of interbreeding with African auroch populations, to the point where some geneticists posit a third separate domestication event in Africa that was then supplemented by cattle imported from Europe and Asia.

Taurine cattle were domesticated from a small founder population of wild aurochs-- perhaps less than 100 animals-- in the Euphrates Valley about 8,000BCE. DNA analysis using both modern and ancient specimens shows little intermixing with the wild aurochs in Europe for most cattle breeds. There is an exception: Highland Cattle and Irish Kerrys share significant ancestry with the European auroch-- in fact, they are genetically more similar to these ancient aurochs than to other European cattle populations. Unlike many other modern breeds of European cattle, Highland cattle can give birth without assistance and will quickly return to a semi-wild state if left to roam. They have historically been used for both dairy and meat.

The first evidence of artificial selection for cattle without horns appears in Europe about 6,000BCE. Although hornless or "polled" cattle became largely extinct after the mid-18th century, the "polled" allele (genetic marker) can be found in Celtic and Frisian cattle populations (Highland Cattle, Kerry, and Holsteins), linking those breeds directly to ancient European cattle raised by Germanic peoples. These cattle show specific traits-- for example, small fat globule size in Kerry milk-- that indicate they were used primarily for dairy.

While different cattle were artificially selected for desirable traits--such as docility, high milkfat percentage, and adaptation to local climates-- throughout their history, the organized creation of cattle breeds did not get underway until the 18th century. In 1760, Robert Bakewell used careful tracking of inherited traits to produce a specialized breed of beef cattle called the Dishley. Within 15 years, the Shorthorn (then called the Durham) was developed by Charles and Robert Colling. In 1822, these cattle were the subject of the first herd book. Following the popularity of the Dishley and the Shorthorn, farmers started using aggressive artificial selection to create new, specialized cattle breeds.

Cattle were introduced to the Western Hemisphere from the Iberian Peninsula in 1493 by Christopher Columbus. These long-horned cows were used for draft work, leather, and meat. Genetic analysis reveals these cattle had a mixture of European and African ancestry. The Spanish were energetic about importing more cows from Europe, as well as breeding more cattle in the Americas over the next hundred years-- there are a variety of letters recording requests from the Spanish colonies for cattle to be shipped from Spain. Cattle were not introduced to northern North America until 1541, when Jacques Cartier brought cattle with him to Haudenosaunee territory in what is now called Quebec. But it was not until the early 1800s that cattle would be imported to North America in large numbers.