Question

The life that exists on Earth today likely arose from a single common ancestor. Judge each statement below and select the ones that explain how natural selection has played a role in the diversity of life on Earth from that single ancestor. Select all that may apply.
Responses
A Natural selection acted on phenotypes that were the result of new mutations in a population.Natural selection acted on phenotypes that were the result of new mutations in a population.
B Natural selection reduced the species numbers on a global scale since individual organisms did not mutate quickly enough.Natural selection reduced the species numbers on a global scale since individual organisms did not mutate quickly enough.
C Natural selection maintained the fitness of populations on a global scale, which maintained species numbers at a constant level.Natural selection maintained the fitness of populations on a global scale, which maintained species numbers at a constant level.
D Natural selection acted on isolated populations separately, allowing for those populations to diverge over time, allowing for speciation.Natural selection acted on isolated populations separately, allowing for those populations to diverge over time, allowing for speciation.
E Natural selection increased the fitness of certain populations as traits that were considered adaptations became more prevalent in the population.

Answer 1

Correct choices: A, D, and E.

- A — True. New mutations (and other sources of heritable variation) produce phenotypic differences, and natural selection acts on those phenotypes.
- D — True. Different selective pressures on geographically or reproductively isolated populations cause them to diverge, promoting speciation.
- E — True. Natural selection tends to increase the frequency of adaptive traits, raising the relative fitness of populations carrying them.

Why B and C are wrong:
- B is incorrect: natural selection can cause extinctions locally or globally, but it is not simply a global reduction of species numbers because organisms “did not mutate quickly enough,” nor is that the primary explanation for the origin of biodiversity.
- C is incorrect: natural selection can maintain fitness via stabilizing selection in some cases, but it does not hold species numbers constant globally and in fact contributes to both diversification and extinction depending on circumstances.