A new investigation of DNA that was obtained from modern cattle and from fossils of their ancient, wild ancestors puts scientists on the horns of a domestication dilemma.
The new data challenge the mainstream idea, based on earlier genetic and archaeological evidence, that herding and farming groups in southeastern Turkey or adjacent Near Eastern regions domesticated cattle perhaps 11,000 years ago. According to that view, these groups then introduced the animals throughout Europe, so current European cattle breeds would trace their ancestry directly back to early Near Eastern cattle.
Instead, cattle domesticated in the Near East interbred with their wild, now-extinct cousins, known as aurochs, already living in some parts of Europe, concludes a team led by geneticist Giorgio Bertorelle of the University of Ferrara in Italy. The domesticated cattle may also have mated with African cattle that had been shipped to southern Mediterranean locales.
“European cattle breeds represent a more diverse and important genetic resource than previously recognized, especially in southern regions,” Bertorelle says. He and his colleagues present their provocative findings in the May 23 Proceedings of the National Academy of Sciences.
The researchers examined chemical sequences of mitochondrial DNA, which is inherited from the mother. Ancient sequences were isolated from five Italian aurochs fossils previously dated at between 7,000 and 17,000 years old. Comparable genetic information was gleaned from more than 1,000 cattle in 51 modern breeds from Africa, Asia, Europe, and North America.
Italian aurochs display mitochondrial-DNA sequences that often occur in cattle today, Bertorelle’s group asserts. The strongest genetic resemblance appears between these aurochs and Italian cattle, followed by less and less similarity in cattle in central and northwestern Europe, the Near East, North America, and Africa.
Greater amounts of genetic variability in cattle from southern versus northern Europe suggest that Mediterranean herders let their cattle roam and mate with wild aurochs, whereas northern herders often kept cattle in guarded areas, Bertorelle adds.
Further analyses showed that certain mitochondrial-DNA sequences found in North African cattle today also commonly appear in breeds from Portugal, Spain, Italy, and Greece, but not areas farther north. Occasional boat transport of cattle from North Africa to southern Europe would explain this finding, in Bertorelle’s view.
Molecular anthropologist Joachim Burger of Johannes Gutenberg University in Mainz, Germany, expresses surprise at the new report. Northern European cattle breeds today derive directly from ancient Near Eastern cattle, according to his group’s recent analysis of mitochondrial DNA from more than 60 modern cattle and 43 aurochs fossils in northern Europe.
“We need to examine genetic data more closely to resolve this issue,” Burger says. Studies of DNA in cells’ nuclei will prove critical, although it’s difficult to extract this genetic material from fossils he notes.
In the meantime, a more thorough investigation will require comparison of mitochondrial DNA obtained from radiocarbon-dated aurochs fossils throughout Europe with that of cattle today, remarks archaeologist Albert J. Ammerman of Colgate University in Hamilton, N.Y.
It’s not clear whether domesticated cattle first moved from northern Africa to southern Europe, as assumed by Bertorelle, or vice versa, Ammerman notes.