Question

A trait exists in a population of a certain species. The trait has two variations, variation X and variation Y. The percentage of the population that has each variation over several generations are shown in the table below.

Generation 1 Generation 5 Generation 10
Variation X 50% 74% 92%
Variation Y 50% 26% 8%

Which statement correctly describes how and why the occurrence of the variations of the trait changed over time?
A.
Variation X became more common because it increases an individual's probability of surviving and reproducing.
B.
Variation Y became more common because it decreases an individual's probability of surviving and reproducing.
C.
Variation Y became less common because it increases an individual's probability of surviving and reproducing.
D.
Variation X became less common because it decreases an individual's probability of surviving and reproducing.

Answer 1

A.

Variation X increased from 50% to 92%, so it became more common. The most likely explanation is that X confers higher survival and/or reproductive success (greater fitness), so organisms with X left more offspring — natural selection favoring X.