Evolutionary change occurs:
a. whenever mutation occurs.
b. whenever allelic frequencies change from one generation to the next.
c. whenever genetic drift is eliminated.
d. both a and b.

D. Both a and b.

Explanation:

Evolution can be define as the heritable changes that occur in the biological population over a successive generation. The heritable changes involves the features and characteristics which are passed on from the parents to their offsprings after the process of reproduction. The evolution occurs due to mutation, genetic variation and genetic recombination. This also occurs when the allelic frequencies change in the gene pool of the species leads to formation of new species.

the law of original horizontality explains:   why rocks appear in layers. correct answer: b the law suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed.   the principle is used by geologists to make assumptions about the relative ages of sedimentary rocks.