How subcultures emerge

Abstract

Sympatric speciation is typically presented as a rare phenomenon, but urban subcultures frequently emerge even in the absence of geographic isolation. Is there perhaps something that culture has but biological inheritance does not that would account for this difference? We present a novel model that combines assortative interaction and multidimensional inheritance. Our computer simulations show that assortment alone can lead to the formation of cohesive clusters of individuals with low within-group and large between-group variability even in the absence of a spatial separation or disruptive natural selection. All it takes is a proportionality between the variance of inputs (cultural 'parents') and outputs (cultural 'offspring'). We argue that variability-dependent inheritance cannot be easily accomplished by genes alone, but it may be the norm, not the exception, in the transmission of culture between humans. This model explains the frequent emergence of subcultures and behavioural clustering in our species and possibly also other cultural animals.

Keywords: Galton–Pearson model; PVDI; cultural divergence; cultural evolution; sympatric speciation.

Graphical abstract

Figure 1.

Model comparison. Offspring distribution function is given by the arithmetic mean of parental values and phenotypic mutation, see Eqns (1) and (2). In a system with pure parental variability-dependent inheritance (PVDI), the proportion of offspring between parental values is constant. In a system with Galton–Pearson (GP) inheritance, the proportion depends on the distance between parental values.

Figure 2.

A graphical summary of the number of subcultures after 200 model generations. The points in the 10-dimensional culture space were normally distributed across all dimensions at the beginning of each simulation run, and 1000 simulation runs were executed for each parameter combination. Red crosses indicate the values of parameters used for single-run examples included in the main article. Blue crosses indicate examples available in the Supplementary Material.

Figure 3.

Two simulation runs, one of a system strongly influenced by GP inheritance (a) and one strongly influenced by PVDI (b). A configuration of points across the first three principal components is displayed at the beginning and after each third of the simulation run. The system with PVDI inhabits the culture space in a discontinuous manner and forms distinct clusters which are stable over time. (See also Supplementary animations 3A and 3B; all supplementary animations are deposited in a separate folder at https://doi.org/10.17605/osf.io/pvyhe, see S6B in the Supplement and the corresponding animation for an approximately intermediate case.) Standardised first three principal components (PC1–PC3 scaled space; for further elucidation see the Methods) rotated to minimise changes between adjacent images are used to visualise the 10-dimensional configuration in 3D scatterplots.