Plasticity-Led Evolution and Human Culture.

Some human traits arise via organic evolution while others are acquired from the prevailing culture via a process of social learning. A mainstream interpretation is that evolution amounts to a change in the relative frequency of gene variants in a population and that culture coevolves at arm's length. Matters look different if one starts instead from the view that organisms are modified during evolution because of changes in gene expression as much as changes in the relative frequency of gene variants. Gene expression, i.e. generation of the product encoded by a gene, is not under genetic control, for it requires location- and time-specific triggers, which cannot be provided by genes. The genes present in an individual are present in every cell, hence at all locations in the individual's body and at all times during the individual's life. The necessary location- and time-specific triggers are provided internally by developmental events and conditions, or externally by environmental events and conditions, i.e. non-genetically. Socially-learned traits, having no special connection with genes, may nevertheless influence evolution, as for any trait. Like organic traits generally, socially-learned traits can be positively or negatively selected, for they similarly influence survival and reproduction. Like learned traits generally, they can play an important role in evolution by providing repeated selective pressure. The resulting evolutionary change typically affects an associated trait (e.g. adult ability to digest the sugar contained in milk), not the socially-learned trait itself (e.g. dairying), which continues under the influence of cultural processes of change.