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DNA analysis of prehistoric humans rarely mated with their cousins, study finds

A DNA analysis of prehistoric humans reveals mating between cousins is more common today than it was over the last 45,000 years ago.

Scientist from Max Planck Society analyzed DNA from remains of 1,785 individuals and found only 54 of the subjects, or three percent, had the typical signs of their parents being cousins.

This is compared to the more than 10 percent of all modern-day global marriages that occur among first or second cousins.

The team notes that the 54 individuals with parents who were cousins did not cluster in space or time, showing that cousin mating was sporadic events in the studied ancient populations.

A DNA analysis of prehistoric humans reveals mating between cousins is more common today than it was over the last 45,000 years ago

According to the study published in Nature Communications, the only ‘archaeological cluster (defined in annotations from the source dataset, modified for readability) with more than two individuals is ‘Iron Age Republican Rome.’

Those with parents who were cousins were also found to have lived in the Pontic-Caspian Steppe region between 2600 and 1500 BC.

And another group was identified in the late pre-contact Andes region.

Notably, 11 of the 54 individuals with long ROH [Runs of Homozygosity, which is a sign parents were cousins] are located on islands: Ordered by time and using the cluster annotations from the publicly available dataset (modified for readability) these are: ‘Sardinia Early Copper Age’, ‘Sweden Megalithic, ‘England Neolithic,’ ‘Chilean Western Archipelago,’ ‘England C-EB,’ ‘Russia Bolshoy,’ ‘Vanuatu 1100 BC,’ ‘Argentina Tierra del Fuego,’ and ‘Indian Great Andaman,’ reads the study.

To compare the ancient DNA with those living today, the team conducted the same analysis with 1,941 modern individuals and found 176 of them had ROH. 

Scientist from Max Planck Society analyzed DNA from remains of 1,785 individuals and found only 54 of the subjects, or three percent, had the typical signs of their parents being cousins

Scientist from Max Planck Society analyzed DNA from remains of 1,785 individuals and found only 54 of the subjects, or three percent, had the typical signs of their parents being cousins

Those with parents who were cousins were also found to have lived in the Pontic-Caspian Steppe (top left) region between 2600 and 1500 BC

Those with parents who were cousins were also found to have lived in the Pontic-Caspian Steppe (top left) region between 2600 and 1500 BC

‘In contrast to ancient data, several geographic clusters of long ROH are found, mainly in present-day Near East, North Africa, Central/South Asia, and South America,’ reads the study.

‘This signal was described previously and mirrors the estimated prevalence of cousin marriages.’ 

To uncover these results, the team designed a new computational tool to screen ancient DNA for parental relatedness.

This method detects long stretches of DNA that are identical in the two DNA copies, one inherited from the mother and one from the father.

The closer the parents are related, the longer and more abundant such identical segments are.

Harald Ringbauer from the Max Planck Institute for Evolutionary Anthropology, the lead researcher of the study, said in a statement: ‘By applying this new technique we could screen more than ten times as many ancient genomes than previously possible.’

According to the study published in Nature Communications , the only 'archaeological cluster (defined in annotations from the source dataset, modified for readability) with more than two individuals is 'Iron Age Republican Rome'

According to the study published in Nature Communications , the only ‘archaeological cluster (defined in annotations from the source dataset, modified for readability) with more than two individuals is ‘Iron Age Republican Rome’

Beyond identifying mating of close kin, the new method also allowed the researchers to study background relatedness. 

Such relatedness originates from the typically many unknown distant relationships within small populations. 

As a key result, the researchers found a substantial demographic impact of the technological innovation of agriculture. 

This was always followed by a marked decay in background parental relatedness, indicative of increasing population sizes. 

By analyzing time transects of more than a dozen geographic regions across the globe, the researchers expanded upon previous evidence that population sizes increased in societies practicing farming compared to hunter-gatherer subsistence strategies. 

Read more at DailyMail.co.uk