Let p represent the frequency of one gene in the pool and q the frequency of its single allele. The algebraic method enables us to work backward as well as forward. Because B is completely dominant over b , we cannot distinguish the Bb hamsters from the BB ones by their phenotype. So, recessive genes do not tend to be lost from a population no matter how small their representation. This is known as the Hardy-Weinberg law in honor of the two men who first realized the significance of the binomial expansion to population genetics and hence to evolution.
Evolution involves changes in the gene pool.
A population in Hardy-Weinberg equilibrium shows no change. What the law tells us is that populations are able to maintain a reservoir of variability so that if future conditions require it, the gene pool can change. If recessive alleles were continually tending to disappear, the population would soon become homozygous. Under Hardy-Weinberg conditions, genes that have no present selective value will nonetheless be retained. To see what forces lead to evolutionary change, we must examine the circumstances in which the Hardy-Weinberg law may fail to apply.