How Do Sickle Cell Genes Protect Tribal People from Deadly Malaria? Is This a Type of Natural Selection?

Abstract

In humans, genetic mutations have led to the formation of several haemoglobin (Hb) variants during human evolution. These mutations usually occur in the genes for a and Β- polypeptide or globin chains of haemoglobin located on chromosomes 11 and 16, respectively. Among these haemoglobin variants, sickle cell haemoglobin (Hb-S) is highly significant in the humans. In fact, this abnormal or mutant haemoglobin is the resultant of a point mutation in the gene for Β-globin, located on chromosome 11. No doubt, this sickle cell gene is relatively more prevalent among tribal people and widely distributed in those geographic regions where the dreaded Plasmodium falciparum-malaria is hyperendemic. In the human population, this mutant gene exists in two forms, the heterozygous (Hb-AS) and homozygous (Hb-SS) states. But this sickle cell gene is also found in association with other mutant genes of erythrocyte or red cell genetic disorders, such as abnormal Hb-C, Β-thalassemia, G-6-PD enzyme deficiency, etc. It is well known that tribal people generally live in forest ecosystem where dreaded malaria is also found to be endemic. How have these tribal people been able to protect themselves from this dreaded malaria for thousands of years in such a hostile environment, when they were most likely to be infected with the malaria parasite? Actually, its secret is hidden in these sickle cell genes only. Tribal individuals who have these genes in the heterozygous state (Hb-AS) do not get malaria or are protected from malaria and lead a healthy life. Several studies have confirmed that AS heterozygote people are protected against malaria. In contrast, those who have these genes in the homozygous (Hb-SS) state (homozygotes) develop sickle cell anaemia, which is fatal. Such patients die early due to severe malaria i.e AS heterozygotee individuals have a double advantages. In fact, it is a type of natural selection and also shows a balanced polymorphism in tribal people which is based on Darwin’s theory. This current communication provides factual and scientific information about the origin of sickle cell genes in the context of natural selection and how these genes protect tribal individuals from malaria. This communication is useful and important for zoologists, scientists working on human evolution, and medical scientists.