Evolution Forces, Species, Isolation and Speciation


Evolution is a complicated process relying on such forces as natural selection, mutation, gene flow, and genetic drift. These forces affect groups of populations known as species and cause variation, which may form a new species. This process is known as speciation. Isolation can ease or hinder this process.

Species, Population, and Variation

Species are the smallest taxon in the biological classification of living organisms. Species are defined as populations or groups of populations of organisms that are isolated from other such groups reproductively. The representatives of species can breed with each other and produce offspring, which is also capable of breeding (Haviland, Prins, Walrath, & McBride, 2013, p. 32). The concept of population is strongly connected with the concept of species, for a population is a group of similar individual living organisms capable of breeding with each other (Haviland et al., 2013, p. 43). As can be seen from the definition of species, in some cases the meanings of “species” and “population” can coincide. The population is the basic concept of genetics. Variation in a range of existing differences within one and the same population. It is known that isolated populations may have a lower level of variability than non-isolated ones. There would be no evolution without variation for the following reason: it leads to biological diversity, which is the goal of four evolutionary forces (Haviland et al., 2013, p. 42).

The Four Forces of Evolution

The term “four forces of evolution” unites natural selection, mutation, gene flow, and genetic drift. Natural selection refers to an evolutionary force that results in adaptation, which is a series of necessary changes to make an organism better adjusted to the environment, in which it lives. Natural selection provides an entire population with a means to survive in certain conditions (Haviland et al., 2013, p. 44). A mutation is a change occurring in genetic material that leads to a new variation (Haviland et al., 2013, p. 43). Unlike natural selection, it happens randomly and can be harmful to an individual (Haviland et al., 2013, p. 42). Similarly to the mentioned two forces, genetic drift results in a genetic change on the population level. Genetic drift is an outcome of random fluctuations in allele frequencies of an individual (Haviland et al., 2013, p. 42). Gene flow is a different way to start a genetic variation. This evolutionary force introduces new alleles to a certain population from other populations. Gene flow depends heavily on the geographic conditions of the environment, in which populations live (Haviland et al., 2013, p. 44).

Isolation and Speciation

The way, in which evolutionary forces are able to affect a population, depends on such conditions as isolation. The concept of isolating mechanisms refers to factors that initiate the separation of populations. If populations are separated, such evolutionary forces as natural selection, genetic drift, and mutation would affect them in a different way, which may lead to the appearance of a new species. By contrast, gene flow would hardly be impossible (Haviland et al., 2013, p. 47). Speciation refers to the whole process of forming new species, which is influenced by isolating mechanisms and directed by evolutionary forces. Speciation can occur in a branching way when two populations are separated by isolating mechanisms; such a process is called cladogenesis. Alternatively, a single population can go through mutations over time and then be recognized as a new species; in this case, the process is called anagenesis. In each case, speciation can occur at different rates (Haviland et al., 2013, p. 47).


In conclusion, species is the population or group of populations of organisms that can produce a new species under the influence of evolutionary forces that cause variation within a species. This process is called speciation. Isolating mechanisms can either facilitate or hinder speciation.


Haviland, W.A., Prins, H.E.L., Walrath, D. & McBride, B. (2013). The essence of anthropology (3rd ed.). Wadsworth, California: Cengage Learning.