Neanderthals and modern man were not meant to get along. The Y chromosome of the former is highly incompatible with the female Homo sapiens.
The alliance between modern man and Neanderthal was not made to last. We were indeed not compatible. Perhaps this is why our two species have never managed to coexist. For the first time, researchers have observed the genome of a male Neanderthal. Their Y chromosome is completely absent from our genetic heritage, they explain in theAmerican Journal of Human Genetics. They also put forward several elements which support the hypothesis of incompatibility.
A great absentee
In our modern human DNA, 2.5 to 4% of the genes come from our Neanderthal cousins. A significant part which is explained by our cohabitation, several millennia ago. But if we have reproduced with this branch of humanity since disappeared, a great absentee remains: the Y chromosome and the genes it carries. “We have never observed DNA from the Y chromosome in a human sample that has never been tested,” explains Fernando Mendez.
Two hypotheses could explain this disappearance. The first assumes that the genes of the Y chromosome have been transmitted to theHomo sapiens, but that they have been evacuated from the genetic heritage with the millennia.
The second theory is supported by this work. To support it, the researchers sequenced the genome of a male discovered in El Sidron, Spain. This is the first time that such research has been carried out. Until now, researchers have been interested in female fossils or mitochondrial DNA – which is passed from mother to child.
Selective miscarriages
The Y chromosome, transmitted from the father, appears to be highly incompatible with pregnancy. The researchers point out that a gene from this segment of DNA was involved in rejection of a male transplant to a woman. They also discovered three major variations from modern humans, minor histocompatibility antigens (HY). They have a function similar to HLA antigens, which are checked to ensure that an organ will not be rejected in the event of a transplant.
In the case of pregnancy, the presence of these antigens could cause an immune reaction against the fetus and a miscarriage. This would explain the absence of genes from the Y chromosome: no male fetus could have reached term under these conditions. This theory seems all the more reliable as currently, spontaneous abortions occur in male fetuses for similar reasons. A solid track therefore, but that the researchers want to confirm with the help of more extensive experiments.
.