For lack of a stamp…

Human evolution with the unavailability of fossil DNA can be tracked by ancient glycans

Marina Astvatsaturyan, Echo of Moscow

Ancient DNA extracted from fossils is a valuable tool for studying evolution and anthropology. But at present, this molecule from earlier geological epochs cannot be found in some parts of Africa, it has been destroyed by heat and high humidity. Researchers from the University of California San Diego (University of California San Diego) and the Kenyan Institute of the Turkana Basin (Turkana Basin Institute) have discovered a biological molecule preserved in conditions that are detrimental to ancient DNA. A new type of glycans – chains of sugar residues – has been isolated from animal remains found in Kenya, which are four million years old. The possibilities of studying the origin of man by glycans are described in the September issue of Proceedings of the National Academy of Sciences.

"In recent decades, many new hominin remains have been found, which were considered as belonging to human ancestors. However, it cannot be that all of them marked the beginning of modern man. Most likely, we descended from only one humanoid species out of many that lived at different times," quotes Ajit Varki, professor at the Faculty of Medicine at the University of California San Diego and lead author of the publication, a university press release (When Ancient Fossil DNA Isn't Available, Ancient Glycans May Help Trace Human Evolution).

The new type of glycans described in the article by Varkey and his colleagues allows us to establish our ancestral line by the exclusion method. 

Glycans are complex chains, the links of which are the simplest carbohydrates – monosaccharides. They are located on the surface of all cells of the body and mediate the interaction between cells and their environment, and also often serve as places of connection with the cell of pathogens. For millions of years, the common ancestors of humans and other monkeys had the same special glycan called N-glycolylneuramic acid (Neu5Gc). But at some point, from two to three million years ago, for reasons possibly related to the fact that it is N-glycolylneuramic acid that malarial plasmodium uses to infect, a survival-friendly mutation occurred that inactivated the human gene responsible for the enzyme, without which the synthesis of this glycan is impossible. The loss of N-glycolylneuramic acid caused a radical change in the molecular appearance of the surface of the cells of the human ancestor, which could create a barrier to crossing with similar hominin species, which contributed to the separation of the line that led to the modern human species. Therefore, if this glycan is found in fossils younger than two million years, then they have nothing to do with humans. 

Portal "Eternal youth" http://vechnayamolodost.ru  19.09.2017