BioConcepts

level of selectionSelektionsebene (ger.)

• A group of entities of similar complexity that is located on one of various niveaus within the hierarchy of biological organization (e.g. genes, cells, individuals, groups, species) and in which natural selection takes place.  
  category selection see also unit of selection

  1944

  It should be noted that Darwin (1859; 6th ed., 1872, p. 52) used the term “struggle for existence” to include not only the life of the individual but success in leaving progeny. That there need be no ambiguity here becomes clear when we consider that two different levels of selection are involved—that of the individual and that of the group. […] Increased competition at one level may therefore mean increased co-operation at a higher level of organization, which in turn means increased efficiency in intergroup competition at this higher level. Similarly, increased co-operation at the lowest levels may lead to increased efficiency in intergroup competition at higher levels, and the relationship just outlined is repeated.Competition andco-perationare each exerting such influences at every level of selection. Individuals are very often selected in terms of social values; and competition, provided it does not become excessive, is very often desirable froma social pointof view.Groups seem to be the usual units of selection.

  Collias, N.E. (1944). Aggressive behavior among vertebrate animals. Physiol. Zool. 17, 83-123: 107; 108. 

  1946

  the human species evolved in the social process, selection always taking place in terms of an integration of individuals to the environment. For individuals the integration with the group and adjustment to the environment through the cultural tradition constitute a total orientation which has its objective forms in the basic routines of mass life. It follows, therefore, that the disturbance of these routines must involve the reorganization of individual behavior at the level of selection that governs the survival of the group, and no individual can escape completely such a reorganization.

  Simpson, G.G. (1946). Notes on a definition of the folk for folk-regional sociology. Social Forces 25, 31-34: 32.
  

  1963

  Levels of Selection [...] The Primary Form of selection in nature, Darwinian selection, takes place between individuals in a population. But competition and selection can and do occur between reproducible biological units lower or higher than individuals on the scale of complexity. The purpose of the present chapter is to survey the operation of natural selection at various levels of organization.

  Grant, V. (1963). The Origin of Adaptations: 230.
  

  1965

  An entire chapter (Chapter 10) is devoted to Levels of Selection, from the gene and the chromosome up to the population.

  Mayr, E. (1965). [Rev. Grant, V. (1963). The Origin of Adaptations]. Evolution 19, 134-136: 134.