The Y chromosome variant in the Basque population emerged during the Bronze Age
A study by the UPV/EHU-University of the Basque Country reveals that the Y chromosome did not come from the Palaeolithic but from the Bronze Age population.
First publication date: 10/06/2021
Following various years of studies, the UPV/EHU’s BIOMICs group has gathered, reviewed and recalculated the data on the origin of a variant of the Y chromosome -the R-S116 variant- present only in the Basque population, and affirms that over 80 % of males in the Basque Country descend from an ancestor who lived 4,500 years ago during the Bronze Age. These results have been published in Scientific Reports, the digital journal of the Nature group.
Chromosomes are the structures that contain most of the genetic material of each individual. The Y chromosome is one of the chromosomes present in males. "It is transmitted only from fathers to male offspring and it is a patrilineal lineage marker that allows us to follow the evolution of the population," explained Marian Martínez de Pancorbo, researcher in the UPV/EHU’s BIOMICs group and author of the study published in Scientific Reports.
In addition, "the Y chromosome has certain variants that arise in an individual and are passed on to his offspring because they remain highly stable over generations. This is the case of the R-S116 variant in the Basque Country’s population; it is a distinguishing feature of more than 80 % of Basque males," she explained. "This work, carried out in collaboration with research staff at the University of Santiago de Compostela and Colorado College, aimed to make an adjusted calculation to find out when this variant of the Y chromosome may have arisen by focusing solely on the population of the Basque Country," added the UPV/EHU professor of Cell Biology.
"To do this, a group of individuals carrying the characteristic R-S116 variant in Álava (75 %), Gipúzkoa (86.7 %) and Bizkaia (87.3 %) was analysed and, by means of certain statistical formulae in which the mutation rate and the time that elapses between one generation and the next are taken into account, the time until the most recent common ancestor is calculated," said Martínez-Pancorbo. "The time that elapses between one generation and another varies greatly, so the estimates of antiquity offer a guide, and rather than being assigned to specific years, they are assigned to a period, in this case, for example, to the Bronze Age, around 4,500 years ago," she added.
"If we study the maternal lineage, we can see that in the Basque Country the Palaeolithic lineage is maintained, in other words, women continue to transmit the ancient Palaeolithic mitochondrial DNA from generation to generation. However, when exploring the Y chromosome, we found that it did not come from the Palaeolithic, but was a new variant from the Neolithic; it is as if a variant arose 4,500 years ago during the Bronze Age and replaced all the Y chromosome lineages of the males who lived in the Basque Country: the ancient hunters, gatherers, etc.," said Marian Martínez de Pancorbo. "We observed that those lineages of Basque males have not continued to be passed down since the Bronze Age, and that the new descendants that appeared are the offspring of these new variants that arrived. This is a very curious fact that attracts a lot of attention and it is not easy to account for it," stressed Martínez de Pancorbo.
"One of the hypotheses put forward is that when the more technologically advanced population arrived from the Eurasian steppe, the males may have had increasing chances of producing offspring with the Basque women. But I wish to emphasise," Martínez de Pancorbo stressed, "that it is still only a hypothesis, since there is no evidence that the males who were present at that time in the territory we know today as the Basque Country were eliminated, because there is no evidence of wars or massacres...". Moreover, "the fact that within such a short time they ended up replacing everything that was around them does not cease to be very curious", the researcher stressed. It could have been due to the fact that the new, technologically more advanced settlers had better possibilities for feeding their progeny and therefore left a greater number of offspring who were passing on the R-S116 Y chromosome.
However, "I personally have another hypothesis," said the professor of Cell Biology at the UPV/EHU, "which we would like to test and which could help us to understand this better. Perhaps the fertility, or the probability of having male offspring, of those individuals carrying the R-S116 variant of the Y chromosome was higher than in males with other types of Y chromosome, and that is why the number of male offspring they left behind increased with each generation. One could conduct a study and simply see whether the individuals currently carrying that variant of the Y chromosome have a higher number of male descendants than the number of male offspring produced by other individuals with other types of Y chromosome variants. But we cannot go back to Bronze Age living conditions, and the current data may not reflect the ancient reality, since under different life conditions individuals may be more or less biologically efficient," said Martínez de Pancorbo.
According to Marian Martínez de Pancorbo, "this study closes a cycle of some very long pieces of work that offer great reliability. However, it should also be noted that how this replacement could have occurred remains open to question, i.e. what was the main reason why the Y chromosome lineages of the ancient inhabitants of the Basque Country virtually disappeared to be replaced by these new variants".
- The Y chromosome of autochthonous Basque populations and the Bronze Age replacement Scientific Reports DOI: 10.1038/s41598-021-84915-1