A new research study says that the Black Plague did not just end up causing the death of millions of Europeans during the 14th century but it also left a mark on the genome of humans living today, preferring those who carry specific immune system genes. These changes could help explain why Europeans have been found to respond in a different way from other people to particular diseases and have diverse resistances to autoimmune complaints.
Geneticists realize that the human population evolves differently when faced with disease. Specific versions of genes help individuals fight against infections in a better way than others do, and persons who have those genes have a tendency to have offspring who also carry the genes than those who do not. This way the favorable genetic version perseveres, while the less strong versions usually end up disappearing because those who have them die off. Such a weeding out of all but the top genes is known as positive selection. However, researchers do have problems locating genes that are positively selected in humans, as most genes do vary from one person to another.
Mihai Netea, who is an immunologist at a Medical Center in the Netherlands, has discovered in his home country of Romania that there is the existence of two very diverse ethnic groups that have helped give him the opportunity to see natural selection at work. Almost a thousand years ago, the Rroma people, which have more commonly been known as the gypsies, moved into Europe from the north of India. But they failed to marry very much with any European Romanians and so they kept distinct genetic backgrounds. However, by living in the same region, each of these groups went through the same situations, and that included the Black Plague. This disease did not reach the northern part of India. So researchers hunted the genes preferred by natural selection by looking for the likenesses in the Rroma people and also European Romanians.
It was found that the Rroma, even today, are very similar to Indians, even though they have lived next to Romanians for almost a thousand years, Netea and his team discovered. Yet there were around 20 genes in both the Rroma and also the Romanians that shown changes which were not noticed in the Indians’ versions of these same genes. They were positively selected in the Romanians and in the gypsies but had not been in the Indians.
The certain genes included one that was for skin pigmentation, one involving skin inflammation and one related to susceptibility to autoimmune diseases. But the genes that Netea was the most enthusiastic about were a collection of three immune system genes discovered on chromosome 4. Those genes look for proteins which fasten on to harmful bacteria inside the human body and launch a defensive response. These genes have to be important for host defense, stated Netea.
Netea believes that the Rroma and Romanians have the same types of these immune system genes because of the evolutionary burden of the Black Plague. Most other Europeans, whose ancestors also lived through the Black Death, are carrying the same changes in these receptor genes. But individuals who live in Africa and China, which are also two other places that the Plague never got to, do not have these gene changes. There have been numerous plagues through history all over the world, but none have ever been as lethal on humanity as the Black Death. It ended up killing every one in four Europeans, and so exercised very resilient selection.
The idea of studying two populations that reside in the same geographical region was a very clever idea, stated geneticist Oscar Lao of Erasmus from Rotterdam, the Netherlands. He was not a part of the study. He stated that the evidence showed the Black Death bacterium did indeed interrelate with the genes favored by natural selection.
The presence of certain versions of genes may give the evolutionary basis for why certain populations seem to be more at risk for certain diseases, stated Douglas Golenbock, who is an immunologist at the University of Massachusetts Medical School in Worcester. The main side effect of all this appears to be that the Europeans have ended up with a more pro-inflammatory immune system than descendants of individuals who never experienced the Black Death. The new research study shows that the Black Plague did not just end up causing the death of millions of Europeans during the 14th century but it also left a mark on the genome of humans, preferring those who carry specific immune system genes.
By Kimberly Ruble
The Chicago Tribune