Cows are seemingly simple creatures. Their story is anything but.
An analysis of the ancient genomes of domestic cattle and their wild relatives has unearthed the complex family tree of our loads producing milk and steak.
The study, published in the journal Science, reveals a story shaped by secular drought and encounters with wild aurochs.
European livestock (Bos taurus) were domesticated about 10,500 years ago in a region populated by wild aurochs, which now covers part of Turkey and the Middle East (Bos primogenius), large animals that were finally extinct in the seventeenth century.
Genetic information from modern cattle indicates that a group of only 80 female aurochs contributed to this initial domestication event. But the analysis of modern genomes can only reveal a lot about this first story.
The introduction of zebu genes (Bos indicus) – the typical South Asian humpback cattle that were domesticated about 8,000 years ago by Indian aurochs (Nomadic Bos). This happened more east in the Indus Valley, a region of modern Afghanistan, Pakistan and northern India.
To address some of the early events in livestock history, geneticist Dan Bradley, of Trinity College Dublin, and his colleagues have minutely extracted DNA from all the bones of cattle that they have. could get.
"We have tried to make as comprehensive a study as possible of the ancient Near East," says Bradley.
It was an ambitious project, given the region in which they worked. With old DNA, "sometimes it's there and sometimes it's not," says Bradley, "and in the ancient Near East, very often, it's not there."
They obtained data on the genomes of 67 cattle, including six aurochs. The animals covered a period of history ranging from 8000 years to the medieval time.
According to the analysis, mating between populations of domesticated and wild local aurochs was frequent.
Aurochs breeding with domesticated cattle were most likely bulls, says Bradley.
"It makes sense," he adds, because bulls do not have to be caught in the wild. Capturing and keeping a wild female auroch would have been much more difficult.
Later, around 4000 years ago, the zebu's genetic signature suddenly appeared.
"There is nothing left, and all of a sudden, everyone is in the area," says Bradley.
One possible explanation is a centuries-old drought. This so-called steep climatic event, lasting for 4.2 thousand years, coincided with the collapse or decline of empires in ancient Mesopotamia, Egypt and the valley of Egypt. # 39; Indus.
"Zebus are better suited to an arid climate," says Bradley.
This trait may have been deliberately introduced by former shepherds of the Near East.
It is also possible that herders simply need to replenish zebu cattle after the drought that has destroyed – or greatly reduced – their taurine herds.
Again, the entrance came from the men's 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 synchronize the introgression of the zebus and correlate it with these periods of drought, it's extremely cool," says geneticist Rute da Fonseca of the University of Copenhagen, who says: Did not participate in the study.
Bradley hopes to obtain more DNA from the region's fossils, in order to reveal in more detail the timing of the zebu influx and the route taken by the zebu cattle from the valley of the island. Indus until the Middle East.
In the meantime, further sequencing could identify the genes at the origin of the characters that separated the first domestic cattle from wild aurochs.
"It would be really interesting to ask what important genes are changing," says Bradley. "Was it called the color of the coat? Was it genes related to lactation – for example, milking? Have there been any changes in the genetics of behavior? These are very interesting questions. "