Polymorphism and Natural Selection in Human Populations (original) (raw)

1. A. C. Allison
2. National Institute for Medical Research, London, England

Excerpt

I should like to begin by considering the abnormal hemoglobins, which provide much the best evidence of polymorphism and natural selection in man. At the Cold Spring Harbor Symposium in 1955 I put forward the following propositions:

1. (1) The homozygous sickle-cell condition is virtually lethal in Africa. In view of the high frequencies of the sickle-cell gene in many regions, the rate of elimination of the gene could not be compensated by recurrent mutation.
2. (2) Balanced polymorphism has resulted because the sickle-cell heterozygote is at an advantage, mainly as a consequence of protection against falciparum malaria.
3. (3) Malaria exerts its selective effect mainly through differential viability of subjects with and without the sickle-cell gene between birth and reproductive age, and to a much lesser extent through differential fertility.
4. (4) High frequencies of the sickle-cell gene are found only in regions where falciparum malaria is, or was until recently, endemic.
5. (5)