GED Science TestLife ScienceMedium
A scientist is studying a population of rabbits in a grassland ecosystem. Over several generations, she observes that the average fur color of the rabbits shifts from predominantly light brown to a darker mottled brown. This change coincides with an increase in the population of predatory hawks in the area. Which of the following evolutionary mechanisms best explains this observed change in rabbit fur color?
- AMutation
- BGene flow
- CNatural selection
- DGenetic drift
Show answer & explanationAnswer & explanation
Correct answer: C. Natural selection
The scenario describes a selective pressure (predation by hawks) favoring rabbits with darker mottled fur, which are likely better camouflaged against the grassland background. This leads to increased survival and reproduction of darker rabbits, a classic example of natural selection.
Why the other options are wrong
- A. Mutation introduces new genetic variation, but it's the *mechanism* by which favored traits become more common (natural selection) that explains the *shift* in the population's average fur color.
- B. Gene flow involves the transfer of alleles between populations, which would typically introduce new variations or homogenize existing ones, not necessarily cause a directional shift due to predation.
- D. Genetic drift is random changes in allele frequencies, typically more pronounced in small populations, and doesn't explain a directional shift linked to a specific environmental pressure.
Natural Selection
The process whereby organisms better adapted to their environment tend to survive and produce more offspring, leading to an increase in the frequency of advantageous traits in a population over generations.
- Requires variation within a population.
- Involves differential survival and reproduction.
- Leads to adaptation to the environment.
- Driven by environmental pressures (e.g., predation, climate).
Memory trick: Natural Selection: Nature Selects the Strongest Survivors.