Question

Use the concept of natural selection to explain why organisms typically adapt over time.

Answer 1

Natural selection explains adaptation by the following logic:

- Individuals in a population vary in traits (e.g., size, coloration, metabolism). That variation arises from mutations, recombination, and genetic mixing.
- Some of those trait differences are heritable: offspring tend to resemble their parents.
- The environment (predators, climate, food, disease, mates, etc.) favors some traits over others: individuals with favorable traits survive and reproduce more successfully than those without them.
- Because favored individuals leave more offspring, the heritable traits that helped them become more common in the next generation. Over many generations, these changes accumulate and the population becomes better matched — “adapted” — to its environment.

Key points and clarifications
- Adaptation is a population-level, not an individual-level, process: individuals don’t change because they want to; allele frequencies change across generations.
- Natural selection is not goal‑directed; it acts on existing variation and is constrained by trade‑offs, genetic correlations, and available mutations.
- The speed of adaptation varies: microbes can adapt in days or weeks (e.g., antibiotic resistance), while larger organisms may take thousands or millions of years.
- Natural selection is one mechanism of evolution; others include genetic drift, gene flow, and mutation.

Example: If a bacterial population is exposed to an antibiotic, rare bacteria with mutations that confer resistance survive and reproduce. Over successive generations the resistant type becomes common — a clear, rapid case of adaptation by natural selection.