VII.2 The presence and the nature of population structures is critical for the nature, speed and often also the direction of microevolutionary processes occurring within the species.
A whole range of evolutionary processes can advance only very slowly in non-structured panmictic populations. According to some theories, for example, the fixation of many patterns of altruistic behaviour is closely related to the existence of competing, gradually emerging and disappearing populations (Kimura 1983a; Koella 2000; van Baalen & Rand 1998; Kerr & Godfrey-Smith 2002). The process of speciation, as well as the ability of members of a species to adapt efficiently to local conditions through evolution, again requires the presence of structured populations. A population partly isolated in terms of reproduction, within which most evolutionary changes take place, is considered by some authors to be the basic unit of evolution, instead of the individual or the species. Thus, gene flow, facilitating exchange of genetic information between populations, is likely to have a crucial and so-far underestimated impact on the course of evolution (Rieseberg & Burke 2001).