Each generation, individuals randomly copy someone from the previous generation. No preference, pure chance. Watch how drift alone can eliminate traits.
Cultural transmission doesn't require any preference or bias. When individuals simply copy a random person from the previous generation, chance alone shapes what survives.
Each new individual picks someone from the previous generation at random and adopts their trait. No evaluation, no preference.
By chance, some traits get copied more than others. Over time, this random variation can push traits to fixation or extinction.
Small populations drift faster. Large populations resist drift. The same force acts on both—only the magnitude changes.
Each colored line is an independent run. The white line shows the mean across all runs. Y-axis is p, the proportion with trait A.
Compare N=20 vs N=5000. Small populations lose diversity fast through drift. Large populations maintain it longer.
Without any preference for A or B, random copying alone can drive one trait to extinction. This is cultural drift—change without selection.
Small populations lose diversity fast. Large populations resist drift. The same random process acts on both—magnitude depends on numbers.
On average, unbiased transmission maintains whatever frequency it starts with. The mean stays near p₀, even as individual runs diverge wildly.