GED Science TestLife ScienceHard
A biologist is studying a population of deer in a newly introduced habitat. Over several generations, she observes that deer with longer legs are better able to escape predators, while deer with shorter legs are better able to navigate dense undergrowth to find food. This leads to a population with both very long-legged and very short-legged deer, while deer with medium-length legs become less common. What type of natural selection is occurring in this population?
- AArtificial selection
- BStabilizing selection
- CDirectional selection
- DDisruptive selection
Show answer & explanationAnswer & explanation
Correct answer: D. Disruptive selection
Disruptive selection favors individuals at both extremes of the phenotypic range over intermediate phenotypes. In this case, both very long legs (for predator escape) and very short legs (for foraging in dense undergrowth) are advantageous, leading to a decrease in the frequency of deer with medium-length legs.
Why the other options are wrong
- A. Artificial selection is selection imposed by humans, not by natural environmental pressures.
- B. Stabilizing selection favors intermediate phenotypes and acts against extreme variations, which is the opposite of what is described.
- C. Directional selection favors one extreme phenotype, leading to a shift in the population's average trait over time, not two extremes.
Disruptive Selection
A type of natural selection that favors individuals at both extremes of the phenotypic range over intermediate phenotypes.
- Favors extreme phenotypes
- Acts against intermediate phenotypes
- Can lead to speciation if extremes become reproductively isolated
Memory trick: SSD: Stabilize, Shift, Divide