Darwin's Evolutionary Theory: Core Concepts and Principles

Charles Darwin and the Theory of Evolution

Charles Robert Darwin (February 12, 1809 - April 19, 1882) was an English naturalist who postulated that all species of life have evolved over time from a common ancestor through a process called natural selection. The outcome was accepted as fact by the scientific community and much of the public in his lifetime, while his theory of evolution by natural selection was not seen as the primary explanation of the evolutionary process until 1930 and now forms the basis of modern evolutionary synthesis. In modified form, the scientific discoveries of Darwin are still the foundational pillar of biology as a science, since they constitute a logical explanation that unifies the observations on the diversity of life.

Key Evolutionary Concepts

Divergent Evolution

Divergent evolution occurs when natural selection pressures cause some populations to become isolated from the rest of their species, leading them to embark on a separate evolutionary path.

Convergent Evolution

Convergent evolution occurs when organisms occupy similar environments and develop similar traits, despite being genetically distant.

Parallel Evolution

Parallel evolution occurs when independent lineages evolve similar traits over time, often due to similar environmental pressures, resulting in descendants that resemble each other and their ancestral forms.

Adaptation

Adaptation is the process by which organisms adjust to their environment, developing traits that enhance their survival and reproduction.

Variations

All organisms possess variable characteristics that arise randomly within each natural population and are inherited by individuals.

Natural Selection

Natural selection is the differential change in the frequency of alleles within a population's gene pool, acting as a positive and creative force of evolution.

Stabilizing Selection

Stabilizing selection favors intermediate phenotypes within a range, while extreme variations are selected against. For example, human infants with birth weights significantly less or more than 3.4 kg often have higher rates of infant mortality.

Disruptive Selection

Disruptive selection favors individuals at both ends of the phenotypic range, selecting against intermediate forms. This leads to a discontinuity in variation, potentially producing two or more distinct phenotypes.

Directional Selection

Directional selection favors individuals at one extreme of the phenotypic range. It shifts the average phenotype of a population over time, leading to evolutionary change in a particular direction.