Practice Questions

Darwin emphasized that natural selection relies on the pre-existing, heritable variations that naturally occur among individuals within any wild population.

Stabilizing selection reduces phenotypic variation by selecting against both extremes (very light and very heavy birth weights), maintaining the intermediate phenotype.

Natural selection is the cause/mechanism, while adaptation (a phenotypic trait that improves fitness in an environment) is the evolutionary effect or outcome.

The selective pressure (tough seeds) favors birds with larger beaks. These individuals survive and reproduce more, increasing the average beak depth in the next generation.

This is natural selection operating through differential reproductive success driven by pollinator preference, leading to a higher frequency of red-flowered offspring.

While Darwin observed heritable variation, he lacked knowledge of Mendelian genetics, chromosomes, and DNA, and could not explain how traits were passed down or how new genetic variations arose.

This is the classic case of industrial melanism (peppered moth). The change in tree bark color causes directional selection, shifting the population curve toward the dark phenotype.

"Descent with modification" is Darwin's definition of evolution, indicating that species are related by common ancestry but have changed over time in response to natural selection.

When humans actively select which individual animals or plants reproduce based on desired traits, the process is known as artificial selection (selective breeding).

Lyell's principle of slow, ongoing geological processes made Darwin realize that the Earth is ancient, providing the vast timescales required for gradual biological evolution via natural selection.