Human ancestors living in Sub Sahara Africa may have interbred with unknown ghost species of early hominins, a study on the evolutionary history of a salivary protein has indicated. This unknown human relative could be a species that has been discovered such as a subspecies of Homo erectus, or an undiscovered hominin, Omer Gokcumen, assistant professor at the State University of New York at Buffalo, said in a recent statement.
After years of sequencing the genomes of female Neandertals, researchers have finally got their first good look at the Y chromosome of a male Neandertal and found that it is unlike that of any other Y in modern humans living today. Even though Neandertals and modern humans interbred several times in the past 100,000 years, the DNA on the Y chromosome from a male Neandertal who lived at El Sidr n, Spain, 49,000 years ago has not been passed onto modern humans, researchers report today in The American Journal of Human Genetics. The finding fits with earlier studies that have found that although living Asians and Europeans have inherited 1% to 3% of their DNA from their ancestors interbreeding with Neandertals, they are missing chunks of Neandertal DNA on their Y chromosomes. This has suggested that female modern humans and male Neandertals were not fully compatible and that male Neandertals may have had problems with sperm production. The new study finds a clue to why: The El Sidr n Neandertal had mutations in three immune genes, including one that produces antigens that can elicit an immune response in pregnant women, causing them to reject and miscarry male fetuses with those genes. So even though male Neandertals and female modern humans probably hooked up more than once over the ages, they may have been unable to produce many healthy male babies (such as the reconstruction of this Neandertal boy from fossils from Gibraltar) and, thus, hastened the extinction of Neandertals.