GED Science TestLife ScienceHard
A marine biologist is studying a population of seals that exhibit varying fur thickness. Over several generations, she observes that seals with thicker fur are more likely to survive and reproduce in colder waters, while seals with thinner fur are more successful in warmer waters. This leads to two distinct groups of seals, each adapted to their respective environments. What type of natural selection is occurring in this population?
- AArtificial selection
- BDirectional selection
- CDisruptive selection
- DStabilizing selection
Show answer & explanationAnswer & explanation
Correct answer: C. Disruptive selection
Disruptive selection favors individuals at both extremes of the phenotypic range over intermediate phenotypes. In this case, both thick and thin fur are advantageous in different environments, leading to two distinct populations.
Why the other options are wrong
- A. Artificial selection is driven by human intervention, not natural environmental pressures.
- B. Directional selection favors one extreme phenotype, shifting the population mean in one direction, not creating two distinct groups.
- D. Stabilizing selection favors intermediate phenotypes, reducing variation, which is the opposite of what's described.
Disruptive Selection
A type of natural selection that favors individuals at both extremes of the phenotypic range over intermediate phenotypes.
- Increases genetic variance within a population.
- Can lead to speciation if the two extreme populations become reproductively isolated.
- Often occurs when different environmental conditions favor different traits within the same population's range.
Memory trick: Disruptive selection pushes populations apart, like a mountain range separating valleys.