Genetics and Evolution - Modern Synthesis Ofevolutionary Genetics

Present-day theories of evolutionary genetics are indebted to Darwin for his groundbreaking descriptions of organisms, individuals, and speciation. Modern theory differs considerably in that it addresses evolutionary mechanisms at the level of populations, genes, and phenotypes—and incorporates understanding of actions, such as genetic drift, that Darwin had not considered.

The modern synthesis of evolutionary theory differs from Darwinism by identifying mechanisms of evolution that act in concert with natural selection, such as random genetic drift. It asserts that characteristics are inherited as discrete entities called genes, and that variation within a population results from the presence of multiple alleles of a gene. The most controversial tenet of modern evolutionary theory is its contention that speciation is usually the result of small, gradual, and incremental genetic changes. In other words, macroevolution is simply the cumulative effect of microevolution. Some evolutionary biologists have instead embraced the theory of "punctuated equilibrium" set forth by Niles Eldredge (1943–) and Stephen J. Gould (1941–2002) in 1972.

Punctuated equilibrium suggests that long periods of stasis (stability) are followed by rapid speciation. It posits that new species arose rapidly during a period of a few thousand years and then remained essentially unchanged for millions of years before the next period of adaptation. Punctuated equilibrium also proposes that change occurred in a small portion of the population, rather than uniformly throughout the population. Although it is different from Darwin's theory of speciation, it is not inconsistent with natural selection; it simply presumes different mechanisms and timetables for the development of new species.