Suppose a new species of snail is found whose shell hardness is controlled by a single gene. The H allele produces a hard shell, while the S allele produces a softer shell. Those with HH genotypes have restricted movement and those with the SS genotypes are more prone to getting eaten by birds. 

(a) You know that the frequency of the H allele in a population is 0.75. What would be the frequency of the genotypes in the population? 

(b) Suppose that both homozygotes have a 75% survival rate and the heterozygotes have a 90% survive rate. What would be the genotype frequencies of the population after selection? 

(c) Has natural selection occurred? Has evolution occurred? Briefly explain the basis of your conclusions