The relationship between genetic traits and the prevalence of diseases such as malaria and smallpox illustrate, the way human biological diversity reflects the adaptation to environmental stresses such as diseases , diet and climate.
For example high prevalence of blood group O studies example in country like india show that blood group O has a less sever malaria as compared to blood group A, B andAB. This suggested that individual with blood O who live within area which is prone to malaria have high resistance to malaria
