For natural selection to occur in a population, which of the following conditions must be met?

Question

Accepted Answer

There must be heritable variation in traits that affect reproductive success. Natural selection requires three conditions: variation in traits among individuals in a population, heritability of those traits (meaning traits can be passed from parents to offspring), and differential reproductive success based on those traits (some variants leave more offspring than others in a given environment). When these conditions are met, alleles associated with traits that increase reproductive success will become more common in the population over generations, leading to adaptation.

If all individuals were genetically identical, there would be no variation for natural selection to act upon, and evolution by natural selection could not occur. While mutations do provide the raw material for genetic variation, they do not need to occur at a constant or predictable rate for natural selection to operate; selection acts on existing variation regardless of how it arose. The environment does not need to remain completely unchanged; in fact, environmental change is often what drives natural selection by altering which traits are advantageous. However, natural selection can also occur in stable environments through competition for limited resources.

Darwin's theory of natural selection, published in "On the Origin of Species" (1859), revolutionized biology and remains the central organizing principle of the discipline. Modern evolutionary biology has integrated Darwin's ideas with Mendelian genetics (the Modern Synthesis), molecular biology, and population genetics to provide a comprehensive understanding of how populations change over time. Understanding the mechanisms and evidence for evolution, including natural selection, genetic drift, gene flow, and mutation, is one of the most heavily tested areas on the CLEP Biology exam.

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