Over the centuries, the evolution of the European population has been determined by multiple natural causes. Indeed, one of the most important causes is the different outbreaks of deadly epidemics that devastated Europe during the last millennium. One such epidemic, the outbreak of bubonic plague or black death in 1348, is probably the best known as it was extremely deadly exterminating between  30% and 50% of Europeans.

Several scientific studies have reached the conclusion that deadly epidemics affect the human immune system since the genes of the immune system evolve under the influence of this type of infectious disease. This is so much so that the people who have the genes that are most  resistant to the disease manage to live and reproduce. However, the carriers of genes that are unable to deal with the disease die.

The most recent study of these characteristics was led by researchers of  the Institute of Evolutionary Biology   (Pompeu Fabra University-CSIC) in Barcelona. In their work, they have discovered that some genes of the immune system have evolved in Rroma and Europeans (Romanians) under the effects of the black death, whereas the same group of genes in people from the north-east of India, where the Rroma originally came from, have not undergone any change. 

The results of this study, which also enjoyed the participation of researchers from the University of the Basque Country and from research centres in The Netherlands, Romania and India, were published on 3 February in the digital edition of the journal  Proceedings of the National Academy of Sciences (PNAS).

To arrive at the conclusion of their study, the scientists of the IBE observed the effect of these infectious processes on those that natural selection acts in the genome of people of both Rroma ethnicity and Romanians. The Rroma coming from the north-west of India settled in Europe just a thousand years ago in the region occupied historically by the Romanians studied, and both groups have lived together since.

The research team took DNA from the three study groups in order to compare their genomes: 100 people of Romanian origin, 100 people of Rroma ethnicity, and 500 current inhabitants of north-west India. The results show that the three genes of the Toll-like receptor group (TLR) of the immune system evolved similarly in the Rroma and the Romanians, under the effect of the selective pressure itself, while the inhabitants of India do not present the effect of natural selection due to this cause. It is a good example of convergent evolution in which the populations of different origins (Romanians and Rroma) adapt similarly upon being subjected to the same environmental hazards, in this case the effect of the plague epidemic.

The relationship between the TLR genes and the bacteria causing plague has been proved experimentally. Therefore, this study shows that plague played a major role in genetic change. Hence, the scientists put blood taken from 101 people of European ascendency in contact with the bacteria that causes the plague,  Yersinia pestis, and they observed a relationship between the TLR genes and an increase in the production of cytokines, molecules that play an important role in the immune system and in resistance to the disease. 

Jaume Bertranpetit, the  IBE researcher who has taken part in this scientific study, is of the opinion that the results "explain some of the differences between Europeans and other peoples as regards their sensitivity to an infectious disease and shows the importance that epidemics have had in modulating the make-up of current human populations. This fact has been highly significant both in the history of humanity and in the way in which the different peoples can provide a response to emerging infections", he adds. 

Reference work:

Hafid Laayouni, Marije Oosting, Pierre Luisi, Mihai Ioana, Santos Alonso, Isis Ricaño-Ponce, Gosia Trynka, Alexandra Zhernakova, Theo S. Plantinga, Shih-Chin Cheng, Jos W. M. van der Meer, Radu Popp, Ajit Sood, B. K. Thelma, Cisca Wijmenga, Leo A. B. Joosten, Jaume Bertranpetit and Mihai G. Netea,  (2014),  " Convergent evolution in European and Rroma populations reveals pressure exerted by plague on Toll-like receptors" ,  PNAS, 3 February.