Reproductive behaviour and natural selection for the sickle gene in the Baiga tribe of central India: the role of social parenting.

We have investigated the transmission of the sickle cell gene in relation to tribal structure, and genetic fitness in a primitive Indian tribal population, the Baiga. Factors operating on gene frequency include protection of AS individuals against falciparum malaria, a high frequency of genetic factors capable of moderating the severity of sickle cell anaemia (alpha-thalassaemia and Xmn I polymorphism in G gamma gene), a high frequency of consanguineous marriage, and reproductive compensation by couples at risk for sickle cell anaemia. The study incidentally made it possible to measure the extent of "social parenting' in such a tribal society for the first time: deviation from expectation in the distribution of the Hb A and S genes within families suggests that up to 30% of children may not be offspring of their ostensible parents.