BIO NMDCAT

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

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

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

Natural selection only acts on traits that influence differential reproductive success. If a trait is completely neutral with respect to fitness, natural selection does not influence it directly.

The inheritance of acquired characters is a postulate of Lamarckism, which Darwinism does not rely on (although Darwin did occasionally speculate on soft inheritance, it is not a core tenet of natural selection).

Because both phenotypic extremes (very long and very short tails) are selected against, stabilizing selection acts to maintain intermediate tail lengths.

Natural selection requires a choice of variants to "select" from. If all individuals are genetically identical, any differential survival is due to chance, and no evolutionary adaptation can occur.

Individuals do not adapt by mutating their own genomes in response to environmental demands. Mutations are random; natural selection simply filters pre-existing genetic variations.

Darwin argued that complex structures evolve via the gradual accumulation of many slight, heritable modifications, with each step improving the organism's fitness compared to the previous state.

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.

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

"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.

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.

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.

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.

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

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).

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.

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