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Figure from:Patterns and Processes in Cultural Evolution

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There is some debate about the role of reaction norms as potential targets of natural selection (see Via et al. 1995) since, at any time, fitness- related traits (e.g., growth or reproductive traits) can vary in their phenotypic expression under different environments (e.g., a plant genotype may produce either large or small leaves if grown under high or low CO, levels, respectively). Thus, natural selection on a trait would be expected to operate on the fitness associated with that trait under a particular environment, rather than on the “potential” expression of the genotypes in different environments. In contrast, when considering behavioral or cultural norms of reaction, individuals may express distinct “behavioral” and “cultural phenotypes” throughout their lifespans, depending on their social/cultural context. In this case, the adaptive value for the capacity to respond differently under distinct environmental contexts (defined by the behavioral/cultural reaction norms) is obvious, particularly if individuals are exposed to variable environments (e.g., variable social or cultural contexts) The concept of “reaction norms” originated from a vast biological literature on phenotypic plasticity, which refers to the phenotypic expression/response of individual genotypes to different environmental conditions (Schlichting and Pigliucci 1998; Pigliucci 2001). Under different environments, individual genotypes may either show no plasticity, if the phenotypic trait under study remains the same (Panel A), or be plastic if trait values change (Panels B and C). The Figure depicts a classical representation of reaction norms associated to four genotypes (represented by distinct lines in the figure) in two different environments (1 and 2). Panel A shows a population with genetic variation (different genotypes) but no plasticity; i.e., each genotype produces the same phenotype in different environments (slope of reaction norms = Q). Panel B represents genetic variation with plastic genotypes that produce distinct phenotypes under different environments (slope of reaction norms # 0), but no genetic variation for plasticity as represented by parallel reaction norms (i.e., no genetic x environment interaction). Panel C shows a population with genetic variation, phenotypic plasticity, and genetic variation for plasticity (1.e., significant genetic x environment interaction)

Figure 1 There is some debate about the role of reaction norms as potential targets of natural selection (see Via et al. 1995) since, at any time, fitness- related traits (e.g., growth or reproductive traits) can vary in their phenotypic expression under different environments (e.g., a plant genotype may produce either large or small leaves if grown under high or low CO, levels, respectively). Thus, natural selection on a trait would be expected to operate on the fitness associated with that trait under a particular environment, rather than on the “potential” expression of the genotypes in different environments. In contrast, when considering behavioral or cultural norms of reaction, individuals may express distinct “behavioral” and “cultural phenotypes” throughout their lifespans, depending on their social/cultural context. In this case, the adaptive value for the capacity to respond differently under distinct environmental contexts (defined by the behavioral/cultural reaction norms) is obvious, particularly if individuals are exposed to variable environments (e.g., variable social or cultural contexts) The concept of “reaction norms” originated from a vast biological literature on phenotypic plasticity, which refers to the phenotypic expression/response of individual genotypes to different environmental conditions (Schlichting and Pigliucci 1998; Pigliucci 2001). Under different environments, individual genotypes may either show no plasticity, if the phenotypic trait under study remains the same (Panel A), or be plastic if trait values change (Panels B and C). The Figure depicts a classical representation of reaction norms associated to four genotypes (represented by distinct lines in the figure) in two different environments (1 and 2). Panel A shows a population with genetic variation (different genotypes) but no plasticity; i.e., each genotype produces the same phenotype in different environments (slope of reaction norms = Q). Panel B represents genetic variation with plastic genotypes that produce distinct phenotypes under different environments (slope of reaction norms # 0), but no genetic variation for plasticity as represented by parallel reaction norms (i.e., no genetic x environment interaction). Panel C shows a population with genetic variation, phenotypic plasticity, and genetic variation for plasticity (1.e., significant genetic x environment interaction)

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Fig. 1 A conceptual model for the causal relationships between the biological and cultural realms. Elements in the Biological Space represent individual genotypes. Elements in the Cultural Space represent cultural phenotypes as determined by the cultural norms of reaction of individual genotypes. The cultural norms of reaction provide a causal link between the cultural products and the biological elements that produce them (represented by the “causal cones” linking the Biological and Cultural Spaces). As with organic diversity, the individual panels (A, B and C) can represent temporal stages towards the evolution of cultural organisms from proto-cultural beings (hence the arrow of Evolutionary Time) or, alternatively, extant species with increasing levels of neural complexity, social organization and cultural development. Arrows within the Biological and Cultural Spaces represent evolutionary trajectories driven by selective processes operating at the gene level (Panel A), co- evolutionary processes between genotypes and phenotypes (Panel B), and independent processes of biological and cultural evolution (Panel C)
Fig. 1 A conceptual model for the causal relationships between the biological and cultural realms. Elements in the Biological Space represent individual genotypes. Elements in the Cultural Space represent cultural phenotypes as determined by the cultural norms of reaction of individual genotypes. The cultural norms of reaction provide a causal link between the cultural products and the biological elements that produce them (represented by the “causal cones” linking the Biological and Cultural Spaces). As with organic diversity, the individual panels (A, B and C) can represent temporal stages towards the evolution of cultural organisms from proto-cultural beings (hence the arrow of Evolutionary Time) or, alternatively, extant species with increasing levels of neural complexity, social organization and cultural development. Arrows within the Biological and Cultural Spaces represent evolutionary trajectories driven by selective processes operating at the gene level (Panel A), co- evolutionary processes between genotypes and phenotypes (Panel B), and independent processes of biological and cultural evolution (Panel C)