Let us begin with Darwin. Darwin provided two important concepts (in his The Origin of Species, 1859) for evolutionary theory: 1) descent with modification, and 2) natural selection acts on individual variation. These indicate that evolution (or change) occurs through the mechanism of natural selection acting on the variation present in a species. What Darwin didn't know was how variation was passed to the offspring from the parents. Mendel discovered how this happens through his work on pea …showed first 75 words of 353 total…

…showed last 75 words of 353 total…Evolutionary Biology (1998) textbook, about 20 tenets of the modern synthesis are listed. Here are some of the more important ones: 1) populations contain genetic variation (from either mutation or recombination), 2) populations evolve by changes in gene frequencies driven by natural selection or drift, 3) evolution commonly occurs through gradual phenotypic change (adaptive variations have small effects), 4) diversification results from speciation, which involves the evolution of reproductive isolation, and 5) all of the above generally occurs over long time periods