What accounts for the fact that polydactylism is prevalent and Tay-Sachs disease virtually absent in ...

What accounts for the fact that polydactylism is prevalent and Tay-Sachs disease virtually absent in
  one human population in the United States, while Tay-Sachs disease is prevalent and polydactylism
  virtually absent in another?
  a. Natural selection has promoted these differences since humans live in many different
  environments.
  b. Mutation rates differ between different loci.
  c. There is little gene flow between the two populations.
  d. The populations are small, and therefore genetic drift is a major factor in the determination
  of allele frequencies.
  e. Genetics is an unpredictable science.

Question 2

One part of Darwin's theory is that individuals with certain traits have an increased competitive edge.
  The source of these traits in individuals is due to
  a. adaptation to the stress.
  b. development over a lifetime.
  c. inheritance from birth.
  d. mutation after birth.
  e. all of these.