MCQs

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.

Stabilizing selection favors intermediate variants by acting against extreme phenotypes, reducing variation and maintaining the status quo of a phenotypic trait.

Natural selection is a non-random, directional process that adapts populations to their environments, whereas genetic drift is random and non-adaptive.

Natural selection can only change the genetic makeup of a population over generations if the phenotypic variations being selected have an underlying heritable genetic basis.

The differing beak morphologies are adaptations developed over generations as ancestral finches colonized islands with distinct food resources (seeds, insects, nectar).

Under Darwinism, variation exists prior to environmental change. Penicillin acts as a selective agent, removing susceptible cells and allowing pre-existing resistant cells to populate.

Evolutionary fitness is defined by reproductive success; an organism must not only survive but also successfully pass its genetic material to fertile offspring.

Malthus's work on human populations made Darwin realize that in nature, overproduction of offspring coupled with limited food and space leads to a struggle for survival.

Natural selection is context-dependent; a trait that is highly beneficial in one environment (e.g., thick fur in the Arctic) may be detrimental in another (e.g., a hot desert).

Disruptive (or diversifying) selection occurs when environmental conditions favor individuals at both extremes of a phenotypic range over those with intermediate phenotypes.

Darwin noted that organisms have a massive reproductive potential (overproduction), yet environmental resources remain stable and limited. This discrepancy inevitably leads to competition or a struggle for existence.