6 ideas
Culture is information stored in human brains and transmitted through teaching and imitation, and it changes over time through processes formally analogous to natural selection, mutation, and drift. Because cultural variants are differentially acquired and retained, populations can be modeled with the same mathematical machinery used for gene frequencies.
Human behavior results from two parallel inheritance channels — genes and culture — each with its own transmission rules, and the two can be tracked simultaneously with coupled equations. Modeling them together reveals dynamics neither channel produces alone, such as cultural traits driving genetic change and vice versa.
Cultural variants spread not randomly but through decision rules that bias which variants people adopt: direct bias (choosing a variant for its intrinsic appeal), frequency-dependent bias (copying the common or the rare), and indirect bias (adopting traits of admired models). These biases act as selective forces that can amplify some ideas and suppress others regardless of fitness consequences.
When people preferentially adopt whatever variant is most common in their group, a frequency-dependent bias kicks in that drives local populations toward uniformity. This conformist tendency maintains sharp behavioral differences between neighboring groups even when migration would otherwise blend them.
Copying others is favored by natural selection because individual learning is costly and error-prone, so relying on the accumulated trials of previous learners is often cheaper than figuring things out alone. This creates a trade-off: too much imitation makes a population unable to track environmental change, so the optimal strategy mixes imitation with some individual learning.
Because cultural transmission has its own selective pressures distinct from genetic fitness, traits can spread that reduce reproductive success — for example, when indirect bias makes prestige markers spread even as they impose costs on adopters. Culture is therefore not merely a tool for biological adaptation; it can pursue its own dynamics that work against the genes.