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.

The slopes of the Tågerup promontory in western Scania contain one of the largest known Mesolithic settlements that has ever been excavated in Scandinavia. The Tågerup site displays a unique combination of huts and houses, graves and wooden implements, flints and bones which constitute a 1500-year-long Mesolithic occupation sequence, dated 6500–5000 cal BC. During that time, there were gradual but far-reaching changes in settlement structure and organization, the use of the landscape, flint technology and food procurement strategies.