From cultural traditions to cumulative culture: parameterizing the differences between human and nonhuman culture

Abstract

Diverse species exhibit cultural traditions, i.e. population-specific profiles of socially learned traits, from songbird dialects to primate tool-use behaviors. However, only humans appear to possess cumulative culture, in which cultural traits increase in complexity over successive generations. Theoretically, it is currently unclear what factors give rise to these phenomena, and consequently why cultural traditions are found in several species but cumulative culture in only one. Here, we address this by constructing and analyzing cultural evolutionary models of both phenomena that replicate empirically attestable levels of cultural variation and complexity in chimpanzees and humans. In our model of cultural traditions (Model 1), we find that realistic cultural variation between populations can be maintained even when individuals in different populations invent the same traits and migration between populations is frequent, and under a range of levels of social learning accuracy. This lends support to claims that putative cultural traditions are indeed cultural (rather than genetic) in origin, and suggests that cultural traditions should be widespread in species capable of social learning. Our model of cumulative culture (Model 2) indicates that both the accuracy of social learning and the number of cultural demonstrators interact to determine the complexity of a trait that can be maintained in a population.Combining these models (Model 3) creates two qualitatively distinct regimes in which there are either a few, simple traits, or many, complex traits. We suggest that these regimes correspond to nonhuman and human cultures, respectively. The rarity of cumulative culture in nature may result from this interaction between social learning accuracy and number of demonstrators.

Evolution in leaps: The punctuated accumulation and loss of cultural innovations

“…Further, there could be a feedback process between the number of tools in a population and the population size: A larger population might be able to invent and retain more tools, but certain innovations also might support a larger population (44,45). Finally, the distribution of traits in the population (as a result, for example, of social stratification) might affect both stochastic and environmentally mediated cultural losses.Several models of the dynamics of cultural evolution explicitly incorporate appearance, transmission, and in some cases disappearance of cultural traits (14,35,40,(45)(46)(47)(48)(49)(50)(51)(52)(53). Sudden dramatic changes in cognition, morphology, or climate are not invoked in these models as a precursor to cultural change; instead, cultural change derives from endogenous properties of the models.…”

“…Further, intermediate-scale environmental change or migration to a new environment also could affect the accumulation and loss of traits that are primarily useful in specific environments (29)(30)(31)(32)(33). In addition, the relationship between the number of cultural traits in a population and population size has been debated (4,14,29,(34)(35)(36)(37)(38)(39)(40)(41); this relationship also might depend on the social learning strategies of the population (42,43). Further, there could be a feedback process between the number of tools in a population and the population size: A larger population might be able to invent and retain more tools, but certain innovations also might support a larger population (44,45).…”

“…Several models of the dynamics of cultural evolution explicitly incorporate appearance, transmission, and in some cases disappearance of cultural traits (14,35,40,(45)(46)(47)(48)(49)(50)(51)(52)(53). Sudden dramatic changes in cognition, morphology, or climate are not invoked in these models as a precursor to cultural change; instead, cultural change derives from endogenous properties of the models.…”

“…Most models of cultural evolution focus on the dynamics of the transmission of cultural traits (40,50,51), often omitting the details of the creative processes underlying the origin of these traits (e.g., refs. 14, 35, and 54).…”

Factors affecting Acheulean handaxe variation: Experimental insights, microevolutionary processes, and macroevolutionary outcomes

“…This does, however, bring the major question regarding the "stability" of the "Acheulean" back full circle. Indeed, as our discussion of the parameter of "heritability" demonstrates, in a situation where imitation is providing a means of social replication, yet sources of variation (i.e., artifactual mutation via copying errors) are ever present, then, profound change via drift and/or or selective "radiation" of new tool forms would be a predicted outcome (see e.g., Kempe et al, 2014), precisely due to the evolutionary mechanisms that we have outlined. Indeed, the combination of high mutation and high potential for variation to be heritable would lead to what biologists call a high capacity for "evolvability" (e.g., Ridley 2004:…”