Effect of Sickle-cell Trait on Resistance to Malaria

It has been remarked above that the difference between sick- ling and non-sickling children is particularly marked at about this level of parasitaemia. It is important to notice that for natural selection to operate in favour of hetero- 7ygouLs sicklers it must exert its effect before reproductive age; the view advanced here is that it can operate only in the absence of acquired immunity, and in an endemic area it is precisely those below reproductive age who lack effective immunity.