Cows are seemingly simple creatures. Their story is anything but.
An analysis of ancient mammalian genomes and their wild relatives has revealed the complex family tree of our milk and roast producing fees.
The study, published in the journal Science reveals a history shaped by centuries-long drought and trysts with wild acorns. Europe's Cattle Bos taurus ) was tamed about 10,500 years ago in a region that today spans parts of Turkey and the Middle East from wild aurochs ( Bos primogenius ), large animals such as eventually sniffed out in the seventeenth century.
Genetic information from modern cattle suggests that a pool of only 80 female aurochs contributed to this initial germination event. But analysis of modern genomes can only reveal so much about this early history.
A complicating factor is the introduction of genes from zebu ( Bos indicus ) ̵
To get hold of some of the early events in the cattle history, geneticist Dan Bradley, from Trinity College Dublin and his colleagues took care of DNA DNA from as many old cattle legs as they could take care of.
"We were trying to make a full study of the ancient Near East we could," Bradley says.
It was an ambitious project, considering the area they worked with. With old DNA, "sometimes it's there and sometimes it's not," says Bradley, "and in the old Near East it's often not there".
They ended up with data from the genomes of 67 cattle, including six aurochs. The animals ranged from 8000 years ago to medieval times.
Previously, feeds between domestic animals of cattle and local wild auros were common, according to the analysis.
Auroch's breeding with the domestic animal was probably bulls, Bradley says.
"It makes sense," he adds, because the bulls need not have been taken away from the wild. Catching and keeping a wild female auroch would have proved much more challenging.
Later, about 4,000 years ago, the genetic signature of the zebu is suddenly unfolding.
"There is nothing, and so suddenly it's all through the region," Bradley says.
A possible explanation is a century-long drought at the time. The so-called 4.2-million-year-old abrupt climate event coincided with the collapse or decline of empires in ancient Mesopotamia, Egypt and the Indus valley.
"Zebu is better suited to a dry climate," Bradley says.
The property may have been intentionally introduced by old Near Eastern shepherds.
It is also possible that shepherds simply had to resume with zebu cattle after the drought was wiped out – or dramatically reduced – their taurine herds.
Once again, the entrance was from the male line. "You can change the genetics of a herd, in years, almost overnight. All you have to do is choose a bull," Bradley says.
"That they can cope with Zebu introgression and correlate it with dry periods is extremely cool," says geneticists Rute da Fonseca from Copenhagen University, who were not involved in the study.
Bradley hopes to get DNA from more fossils from the region, to reveal in detail the timing of the influx of zebu and the path taken by the zebu cattle from the Indus Valley to the Middle East. Deeper sequencing was able to identify genes behind the properties that separated early cattle from wild aurochs.
"It would be very interesting to ask which are the major genes that are changing," Bradley says. "Should it be called coat color? Were there genes linked to lactation – for example, milking? Were there changes in the genetics of behavior? These are really interesting questions."