Cows are seemingly simple creatures. Your story is anything less.
An analysis of ancient genomes of domestic livestock and their wild relatives has uncovered the complex family tree of our milk and meat production burdens.
The study, published in the journal. Science, reveals a history formed by a drought of centuries and encounters with wild uros.
European cattle (Bos taurus) were domesticated about 10,500 years ago in a region that today covers parts of Turkey and the Middle East from wild uros (Bos primogenio), great beasts that were finally extinguished in the seventeenth century.
The genetic information of modern livestock indicates that a group of only 80 female uros contributed to this initial domestication event. But the analysis of modern genomes can only reveal a lot about this early history.
A complicating factor is the introduction of zebu genes (Bos indicus) – the characteristic humpback cattle of South Asia that was domesticated about 8000 years ago by Indian uros (Bos nomadicus). This happened farther east in the Indus Valley, a region in present-day Afghanistan, Pakistan and northern India.
To learn about some of the first events in cattle history, geneticist Dan Bradley of Trinity College Dublin and his colleagues meticulously extracted the DNA from as many old cattle bones as they could.
"We tried to do as complete a survey of the ancient Near East as we could," says Bradley.
It was an ambitious project, given the area in which they were working. With ancient DNA, "sometimes it's there and sometimes it's not," Bradley says, "and in the ancient Near East, it's very often not there."
They finished with data from the genomes of 67 cattle, including six uros. The animals went through a period of history from 8000 years ago to medieval times.
At first, according to the analysis, matings between domesticated livestock populations and local wild uros were common.
The aurochs that breed with domesticated cattle were probably bulls, says Bradley.
"That makes sense," he adds, because bulls do not need to have been captured from nature. Capturing and keeping a wild female Auroch would have been much more difficult.
Later, about 4000 years ago, the zebu's genetic signature suddenly appears.
"There's nothing, and then, all of a sudden, it's in the whole region," says Bradley.
A possible explanation is a drought of centuries in the moment. The so-called abrupt climate event of 4.2 thousand years coincided with the collapse or decline of the empires in ancient Mesopotamia, Egypt and the Indus Valley.
"Zebu are better adapted to an arid climate," says Bradley.
The trait may have been introduced deliberately by the ancient pastors of the Near East.
It is also possible that the shepherds simply need to replenish zebu cattle after the drought has ended, or drastically reduced, their bullfighting herds.
Once again, the entrance was of the male line. "You can change the genetics of a herd, in terms of years, almost overnight. All you have to do is choose a bull, "says Bradley.
"That they can time the introgression of Zebu and correlate it with these periods of drought is extremely great," says geneticist Rute da Fonseca of the University of Copenhagen, who was not involved in the study.
Bradley hopes to obtain DNA from more fossils from the region, to reveal in greater detail the timing of the Zebu influx and the route that Zebu cattle took from the Indus Valley to the Middle East.
Meanwhile, deeper sequencing could identify genes behind the traits that separated early domestic cattle from wild uros.
"It would be really interesting to ask what are the important genes that are changing," says Bradley. "It was called a color layer? Were the genes linked to breastfeeding, for example, milking? Were there changes in behavioral genetics? These are really interesting questions. "