31 March 2020
Ancient cattle DNA reveals a bullish tale
Published online 12 July 2019
Genome-wide analyses of ancient cattle remains provide insights into breeding patterns and links with climatic shifts across the Fertile Crescent.
The study of ancient DNA from fossilised animal remains can help scientists understand species adaptation, and early farming and domestication patterns. Now, an international team has sequenced the genomes of 67 ancient cattle remains, giving insights into 8,000 years worth of cattle breeding. Their results suggest that breeding patterns hold intriguing links to past climatic events, and may point towards farmers making decisions to ensure the survival of their herds.
The researchers, led by Daniel Bradley at Trinity College Dublin, Ireland, and including Abdelsalam Mikdad at the Institut National des Sciences de l’Archeologie in Rabat, Morocco, extracted DNA from the remains of three different cattle species. These included the domesticated Bos taurus, the wild zebu cattle Bos indicus that originated from the Indus Valley (in Pakistan and northwest India), and six ancient aurochs – the now-extinct wild cattle that once roamed Europe and Asia.
“Bos taurus are the earliest domesticated cattle and originated from the Near East, in Anatolia, the Levant and Iran,” says Bradley. “All modern cattle descended from a small pool of B. taurus domesticated around 10,500 years ago. However, early genetic details are masked in modern cattle DNA. The only way to properly reconstruct the genetic past is to use ancient genomics,” says Bradley.
The team extracted DNA from the cattles’ inner ear bones, which are known to have the best DNA preservation rates, particularly in arid countries such as the Middle East where many of the ancient remains were found.
Domesticated B. taurus and the zebu B. indicus lived separately for thousands of years. However, the team’s results suggest that, quite suddenly around 4,200 years ago, zebu bulls began to breed with B. taurus right across the Fertile Crescent, an area of the Middle East that includes modern-day Iraq and Egypt. This breeding event coincided with a multi-century drought in the region and the associated collapse of the Egyptian and Mesopotamian civilisations. Farmers may have made a deliberate choice to allow breeding with the arid-adapted zebu to safeguard their herds in the face of climatic changes.
“While whole genomes changed dramatically in B. taurus, the maternally inherited mitochondrial DNA pool was hardly affected. This points to [zebu] bulls impregnating female B. taurus, rather than mixed male and female breeding across both species,” says Bradley.
The researchers also uncovered new details regarding breeding with aurochs in early cattle populations; in particular that auroch input made the cattle of the Southern Levant genetically distinct from other early domesticated cattle.
“This study of ancient Near Eastern cattle has very interesting parallels to what we know about human populations from ancient DNA,” says Harvard Medical School geneticist Iosif Lazaridis, who was not involved in the research but has done extensive genetics work on early humans and agriculture. “South Asia, which is where Bos Indicus originated, was not isolated during this period. People seem to have migrated from the Indus Valley civilization into Central Asia around the same time as the climatic effect that happened around 4,200 years ago. This may have introduced zebu cattle ancestry into Near Eastern cattle populations.”
Verdugo, M.P. et al. Ancient cattle genomics, origins, and rapid turnover in the Fertile Crescent. Science 365, 173–176 (2019).