How can sickle cell anaemia be described in terms of natural selection?
Firstly, some background facts about malaria: – Malaria kills about 2 million people per year, most in Africa, mostly children. – Malaria is caused by a parasite, any one of four Plasmodium species, which infects, among other cells, the red blood cells, where it divides asexually. Someone with the sickle cell trait has a higher chance of surviving to adulthood than someone without the trait. Even though the trait may cause mild anaemia, those with the trait are generally quite well. If a parasite enters a cell of a person with the sickle cell trait, then that cell will sickle (shrivel) and it will be destroyed, along with the parasite, by phagocytic white blood cells (monocytes). This gives that person good protection against malaria. Anyone without the trait may die, or may be sick for quite a long time, may suffer liver damage, cerebral haemorrhage, and other damage. Anyone with the sickle cell disease, that is, homozygous Haemoglobin S, will have sickle cell crisis when the body is
