scientists think that two species with homologous structures probably had a common .
a. fossil
b. ancestor
c. offspring
d. environment

Name the part of the the brain labeled "e".

Which of the following was not a major animal on land during the carboniferous period? amphibians insects both a and b none of the above

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.