Question

Which graph best represents disruptive selection?

Graph A has trait value on the horizontal axis and population of individuals on the vertical axis. The original population increases, decreases, increases, and then decreases again. The population after selection increases at the point that the original population drops.
Graph A

Graph B has trait value on the horizontal axis and population of individuals on the vertical axis. The original population and population after selection have similar curves, but the original population peaks before the population after selection.

Graph B

Graph C has trait value on the horizontal axis and population of individuals on the vertical axis. The original population peaks at the same time as the population after selection but the original population peaks higher and at a more rapid speed.

Graph C

Answer 1

Graph A.

Disruptive selection favors extreme trait values and selects against the intermediate, producing a bimodal distribution (peaks at both extremes and a dip in the middle). Graph A shows that pattern. (By contrast, Graph B illustrates directional selection — the whole peak shifts — and Graph C reflects stabilizing selection — a taller, narrower central peak.)