Summary of Chapter Concepts

The process of evolution depends on genetic variation. Among and within populations, genetic variation is caused by the presence of different alleles, which can be dominant, codominant, or recessive. Genetic variation can be generated through mutation or recombination.

Evolution can occur through random processes or through selection. The four random processes that cause evolution are mutation, genetic drift, bottleneck effects, and founder effects. Evolution can also occur by selection, which can be stabilizing, directional, or disruptive. Whether evolution occurs by random processes or by selection, scientists can use similarities in traits to arrange hypothesized patterns of relatedness among different groups on phylogenetic trees.

Microevolution operates at the population level. Populations can evolve due to artificial selection to produce breeds of domesticated animals and plants. Populations can also evolve due to natural selection, such as when predators selectively consume prey and when pesticides and antibiotics selectively kill the most sensitive individuals, allowing the most resistant individuals to survive and reproduce.

Macroevolution operates at the species level and higher levels of taxonomic organization. The most common process causing macroevolution is allopatric speciation in which populations become geographically isolated and independently evolve to become distinct species over time. The less common process is sympatric speciation in which species become reproductively isolated without being geographically isolated, often by forming polyploids.

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