Which option best summarizes the basic concept of natural selection in evolutionary biology?

Introduction / Context:
Natural selection is one of the central mechanisms of evolution described by Charles Darwin and others. It explains how populations change over generations when some individuals leave more offspring than others. This question asks you to choose the statement that best summarizes the concept of natural selection, without adding unrealistic guarantees about adaptation or mutation.

Given Data / Assumptions:

Populations contain heritable variation in traits.
Environments present challenges and limited resources.
Reproductive success differs between individuals.

Concept / Approach:
Natural selection occurs when individuals with certain heritable traits have higher survival and reproductive success in a particular environment. As a result, those traits become more common in the population over time. This does not mean that organisms always adapt perfectly or that every mutation is beneficial. Many mutations are neutral or harmful, and some lineages go extinct despite selection. Therefore, the best summary emphasizes differential survival and reproduction linked to fitness, not automatic adaptation or guaranteed progress.

Step-by-Step Solution:
Step 1: Identify the essential elements of natural selection: variation, heritability, differential survival, and differential reproduction. Step 2: Examine each option to see whether it captures these ideas without exaggerating. Step 3: Recognize that the option stating that the fittest organisms survive and reproduce more is closest to the classic description of natural selection. Step 4: Reject options that claim organisms always adapt or that all mutations are beneficial, because these claims are not supported by evolutionary theory.

Verification / Alternative check:
Textbook definitions of natural selection often read that individuals with traits better suited to the environment tend to survive and reproduce in greater numbers. Over many generations, this leads to adaptation. None of these definitions guarantee success for every individual or suggest that every mutation improves fitness. This matches the wording of the correct option and confirms it as the best summary.

Why Other Options Are Wrong:
Organism will always adapt: Some species fail to adapt and become extinct; adaptation is not guaranteed for every lineage.
Organism will always mutate to survive: Mutations occur randomly with respect to need; they are not directed by survival requirements.
Mutation always makes species fitter: Many mutations are neutral or harmful. Only some improve fitness, and selection then favors those.

Common Pitfalls:
A frequent misconception is that evolution is progressive or goal directed, as if species always move toward perfection. Another error is to think that organisms intentionally change in response to environmental challenges. Natural selection is a blind process that acts on existing variation. Remember that it simply favors traits that, by chance, confer better reproductive success in a given environment.

Final Answer:
Natural selection is best summarized by the idea that the fittest organisms survive and reproduce more successfully than others, causing advantageous traits to become more common over time.