1st ESO

3rd ESO

4th ESO

Biology 2nd Baccalaureate

Index by courses



Skip navigation

4.3.4. Other evolutionary theories

Other current theories about evolution

Some other theories about evolution are:

Theory of punctuated equilibrium or punctualism or intermittent equilibrium

When studying the fossil record, paleontologists questioned the gradualism asserted by the synthetic theory of evolution. If gradualism were true, there should be a multitude of fossils with intermediate characteristics between one species and another, showing a slow and continuous change in evolution. But in many cases, one species suddenly disappears and another appears.

According to some paleontologists, such as Stephen Jay Gould, they believe that the theory of punctuated or intermittent equilibrium (1972) is more correct. According to this theory, species spend a long time without any change or with minor changes (periods of time called stasis), but at certain times, some species have periods of very rapid change.

Punctualism should not be confused with saltationism. The saltationism postulates that appear new species in a single generation, and punctualism is not in favor of that.

The punctualism does not deny the neo - Darwinism, but proposes an explanation for cases in which a rapid diversification of species occurs.

For example, in the Cambrian there was a great diversification of species that could not be explained by the gradualism of Neo - Darwinism.

Comparación entre el gradualismo y el equilibrio puntuado

By Miguel Chavez, modified by wooptoo (Own work) [Public domain], via Wikimedia Commons

Neutralist theory or neutralism

The Japanese biologist Motoo Kimura, in 1968 proposed the neutralist theory, in which he tried to adjust the synthetic theory of evolution to the new knowledge of molecular biology. Kimura believes that most mutations are neither beneficial nor harmful, they are neutral. Therefore, natural selection does not influence mutations.

Although he does not deny the importance of natural selection in adaptive evolution, he believes that genetic drift of mutants is more important. That is, whether there are more or fewer alleles in a population depends on chance, in the form of genetic drift, not on selective pressure.

The neutralist theory speaks of a molecular level, since at the macroscopic level it continues to affirm that natural selection is the evolutionary engine.

Selfish gene theory

The selfish gene theory is similar to the neo-Darwinian one , but states that the fundamental evolutionary unit is the gene , rather than the individual. There is a competition between genes, not individuals, and the purpose of evolution is to increase the frequency of certain genes over others within the population.


Legal warning






Follow us if it has been useful to you

Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.