To observe natural selection's effects on a population, which of these must be true?
A. Members of the population must increase or decrease the use of some portion of their anatomy.
B. The population must contain genetic variation.
C. One must observe individual organisms undergoing adoption.
D. One must observe more than one generation of the population, and members of the population must increase or decrease the use of some portion of their anatomy.
E. One must observe more than one generation of the population, and the population must contain genetic variation.