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MCAT Biology Question — Natural Selection

The Modern Synthesis in evolutionary biology reflects the current consensus about how evolution proceeds. According to the modern synthesis, which of the following is a correct characterization of a principle of natural selection?

A) Most mutations that occur in a species that is well-adapted to its niche are likely to be harmful.
B) Those individuals within a species that reproduce in the greatest numbers are fittest.
C) Genetic drift has no impact on the overall gene distribution in a population.
D) Ecosystems across all niches can only support a finite population of each organism.



One of the basic assumptions of natural selection is that organisms produce more offspring than the environment is capable of supporting. Then, some of those individuals survive to reproduce and others don’t – which survive are controlled by natural selection through environmental forces. That best matches choice (D).

A) False. Most mutations are silent or neutral as they occur in “junk DNA” or non-coding regions of the genome.
B) Tempting, but not technically true. Fitness is determined by the number of fertile offspring that survive to reproduce, not simply the total number of offspring.
C) Genetic drift is a form of random change in the gene distribution.
D) correct

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