1. Biological evolution is change in allele frequencies in populations. Evolution has occurred in the past and is constant and ongoing.
2. Evolution consists of large-scale, species-level changes (macroevolution) as well as gene-by-gene changes (microevolution).
3. Before Darwin, attempts to explain life's diversity were human-centric and subjective. Lamarck was the first to propose a mechanism of evolution, but it was based on acquired rather than inherited traits.
4. Geology laid the groundwork for evolutionary thought. Some people explained the distribution of rock strata with the idea of catastrophism (a series of floods). The more gradual uniformitarianism (continual remolding of Earth's surface) became widely accepted. The principle of superposition states that lower rock strata are older, suggesting a time frame for fossils within them.
14.2 Charles Darwin's Voyage
5. During the voyage of the HMS Beagle, Darwin observed the distribution of organisms in diverse habitats (biogeography) and their relationships to geological formations. He noted that similar adaptations can lead to convergent evolution. After much thought, and considering input from other scientists, he synthesized his theory of the origin of species by means of natural selection.
6. The bountiful evidence in Darwin's treatise is organized as "one long argument." However, people who believed Earth to be young, humans to be unique, and nature to move toward perfection, had difficulty with his ideas.
7. Darwin's theory was based on the observations that populations include individuals that vary for inherited traits; that many more offspring are born than survive; and that life is a struggle for use of limited resources. According to the theory of natural selection, individuals least adapted to their environments are less likely to leave fertile offspring, and therefore their genes will diminish in the population over time. The genes of those better adapted to the particular environment will persist. Natural selection caused the diversification, or adaptive radiation, of finches on the Galápagos Islands.