Lactose intolerance has been shown to have been around back in the Bronze Age. Researchers of a new study analysed the genomes of 101 Bronze-Age Eurasians and found that 90 % of them were lactose intolerant. The results of the study also revealed the possible ways in which modern Europeans have developed their particular physical traits like blue eyes and light skin. The findings have been published in the journal Nature.
40,000 years ago, modern humans migrating from Africa reached Europe, and the north, west and central Asia. The descendants of these groups of people now can be recognised by their specific physical features: light skin, eye and hair colours, and lactose tolerance.
The particular physical traits of modern Europeans might come from different ancient communities. For instance, blue eyes might originate from hunter gatherers in Mesolithic Europe (10,000 to 5,000 BC). Other features might have developed later from people coming from the East.
This was found after the researchers revealed the possible geographical distributions of genetic variations that were around at the start of the Bronze Age: these were very different from what they are today, but, by the end of that era, similarities were detected. This might be interpreted as meaning that migration and replacement of peoples happened on a level not documented before.
The question is, how come the common traits now found in western Eurasia were rare in African ancestors? The DNA of hunter gatherers from Europe might hold the answer to this: they had a combination of features, like dark skin with blue eyes. It was suggested that blue eyes might trace back to European hunter gatherers of the Mesolithic period (10,000-5,000 BC).
On the other hand, the mutations behind light skin were rare in the Mesolithic, but were present in a great proportion in people living in the Bronze Age (3,000 years later) in Europe and the steppe. The two areas had witnessed migration of Middle Eastern farmers afterwards; perhaps the mutations came from there. The researchers suggested that these people were driven by natural selection such that the production of vitamin D was allowed in high amounts in spite of little sunlight.
Yet another trait seen in modern Europeans is lactose tolerance. It was initially thought that this mutation was widespread during the Bronze Age. But, only 10 % of them were lactose tolerant. The most individuals with the mutation were the Yamnaya people and their descendants. This might have thus come from the steppe and the Yamnaya.