Sickle-cell anemia is an inherited human disorder caused by a recessive s allele that produces abnormal hemoglobin in red blood cells. A large number of individuals with the ss genotype die before reaching adulthood. Because of this, you might expect that the s allele would have a low frequency in the gene pool. However, when geneticists studied certain populations, they found that the recessive allele has a surprisingly high frequency (0.2 to 0.4) in some parts of Africa. These areas also have a high incidence of malaria. Further investigation showed that people with the SS genotype often died of malaria. However, people with the Ss genotype did not contract malaria. Which of the conditions required for Hardy-Weinberg equilibrium is not met in the case of the Ss genotype in these populations of Africans?