2. Which of these is a factor needed for natural selection to occur? a. Different fitness levels of the offspring
b. Overproduction of offspring?
c. Variation is heritable
d. All of these
e. None of these

in the year 2850, humans successfully colonized mars. the martian modules that were constructed could hold only a small population of people. it is now a century later, and the population on mars has grown to 600 people. of the current mars population, 45 people express the recessive phenotype for phenylketon- uria (pku) syndrome (pp genotype).

explanation: