Evolution in primates by “Catastrophic‐selection” interplay between enveloped virus epidemics, mutated genes of enzymes synthesizing carbohydrate antigens, and natural anti‐carbohydrate antibodies

Abstract

“Catastrophic‐selection” is an evolutionary mechanism, by which entire parental‐populations are eliminated but very few mutated offspring survive and replace extinct parental‐populations. The human natural anti‐carbohydrate antibodies, anti‐Gal and anti‐Neu5Gc suggest the occurrence of catastrophic‐selection events in primate evolution. Parental‐populations synthesizing corresponding carbohydrate‐antigens underwent extinction in viral epidemics, and few offspring survived. These offspring carried accidental mutations that inactivated carbohydrate‐antigen synthesis and produced natural‐antibody against the lost antigen. Such natural anti‐carbohydrate antibody was produced against environmental carbohydrate‐antigens (e.g., gastrointestinal bacteria). The carbohydrate‐antigen in infected parental‐populations was also synthesized on viruses by the host glycosylation‐machinery. The natural‐antibody in the offspring bound to the carbohydrate‐antigen on infecting viruses produced in parental‐populations, destroyed the viruses and protected these offspring from extinction. This process occurred in ancestral Old‐World monkeys and apes synthesizing α‐gal epitopes, which were replaced 20–30 million‐years‐ago by offspring lacking α‐gal epitopes and producing natural anti‐Gal antibody against this antigen, and later in hominins synthesizing the sialic‐acid antigen Neu5Gc, which were replaced by offspring lacking Neu5Gc and producing anti‐Neu5Gc antibody. A present‐day example for accidental mutations in very few humans that lost a common carbohydrate‐antigen and produce a natural antibody against it is the rare blood‐group “Bombay” individuals. These individuals lack the H‐antigen (blood‐group O) which is synthesized in all other humans, and produce the natural anti‐H antibody against blood‐group O. Overall, it is suggested that natural anti‐carbohydrate antibodies played a critical role in preventing complete extinction of mammalian species in epidemics of highly virulent viruses and may have similar role in future events.