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According to a new study, scientists have found traces of the human civilization of the Bronze Age in an ancient cattle DNA.
The research team collected and sequenced DNA samples from former domestic and wild cattle, or aurochs, to tell the story of livestock domestication in the Fertile Crescent, a region now defined as Middle East and the Levant. The findings reveal a sudden introduction of DNA from another breed of cattle from the Indus Valley, possibly due to the fact that humans have adapted to a sudden change in climate .
"The ancient DNA opens a window on the past, unlike modern genes, especially for domestic animals and artificially selected and manipulated species," studies the first author, Marta Verdugo, from now on. technical support specialist. at Oxford Nanopore Technologies, told Gizmodo.
Cattle are native of an animal called the Eurasian auroch and were first domesticated by primitive human civilization in the fertile crescent – but scientists do not know what it really is about how the extinct auroch became the cow of domestic breeding. For example, it is not known how modern herds of the Middle East (derived from Bos taurus cattle of European origin) contain as much South Asian zebu DNA as "as different as humans and Neanderthals," said study author Daniel Bradley of Trinity College. Perhaps wild aurochs have exchanged their DNA between herds – or perhaps cattle breeders have raised them actively.
They extracted DNA from 67 old cattle samples and analyzed the origins of their genetic code. The first few thousand years of domestic cattle mark various origins, with various introductions of auroch DNA. Although zebus cattle are 8,000 years old and there is further evidence of the interaction of the Indus Valley and Fertile Crescent civilizations, scientists have not detected zebu DNA in genomes cattle from the Middle East until 4000 years ago, according to the newspaper. published in Science.
However, about 4,000 years ago, hybrid animals containing large amounts of zebu DNA began to appear in the data set.
This 4,000-year mark is another important period of human civilization: a period of climate change and long drought, as well as the decline of empires in the Fertile Crescent, in Egypt and in the Indus Valley. . The scientists behind the study hypothesized that people were intentionally introducing more drought-tolerant zebus into their flocks to cope with environmental changes. This influence remains present in today's domestic livestock.
The study of ancient DNA of course has its challenges. DNA is degrading over the centuries as there is no biological process to maintain it, and this degradation occurs more quickly in warm environments. Verdugo explained that a dense part of the skull's temporal bone, called the petrous part, is particularly effective in preserving old DNA. In the end, they were able to obtain an average coverage of 0.9 times, which means that on average, the probability that each fragment of the genome is covered once is about 90%. This is not very high compared to the sequencing of the modern genome, but hey, this DNA is thousands of years old.
The research is "fantastic," said Lawrence Frantz, lecturer in molecular genetics and computer science at Queen Mary University in London, who did not participate in the study. Frantz explained to Gizmodo that the old DNA methodology took into account potentially missing information from sequencing mitochondrial DNA, since it was probably bulls introducing their DNA into the flock and that mitochondria were (usually) inherited only from the mother. He thought that the massive influx of zebu DNA at such a precise moment was not totally unexpected and validated some long-held archaeological theories.
He warns that the reason for the influx of zebu DNA is not yet certain and that the quality of the data is probably not sufficient to validate the hypothesis that they were introduced because they were more resistant in arid environments. "The next step is to actually validate the hypothesis that there was a biological reason for that and not just an influx of zebu for another reason that had nothing to do with the climate. "
There are certainly other stories of ancient civilizations (and cattle) written in this ancient DNA, while aurochs interacted with these nascent domestic herds. It's just a matter of finding and sequencing that old DNA before it's lost through time.
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