Question

Babies with very low or very high birth weight are less likely to survive. The graph shows the percentage of babies born at different weights.

A graph entitled Percentage of Babies born at Different Weights has weight in pounds on the horizontal axis, and percentage on the vertical axis. A small percentage of babies are born at the low and higher birth weights, and a greater amount are around 7 to 8 pounds.

Which statement is a valid claim that could be made using the data in the graph?
Directional selection is occurring because the graph favors an extreme.
Stabilizing selection is occurring because the average is favored.
Disruptive selection is occurring because the two extremes are favored.
Biodiversity variation is occurring because there is an increase in trait variation.

Answer 1

Stabilizing selection is occurring because the average (intermediate) birth weight is favored. The graph shows most babies near 7–8 lb and fewer at the low and high extremes, and survival is lower at those extremes, so selection favors the intermediate phenotype.