When some ideas are more compelling than others. Explore how content-based preferences shape cultural selection.
Some ideas stick. A memorable story, an effective technique, an intuitive explanation— these get copied more readily. This is direct bias: preference based on the trait itself.
Each person encounters a random demonstrator. But whether they copy depends on what they see—some traits are more compelling.
The difference between copying probabilities (s_a - s_b) determines selection strength. Larger gaps mean faster change.
Selection is weakest when the favoured trait is rare or dominant. It's strongest at 50-50—maximum variation, maximum pressure.
Each generation, everyone observes a random person. They copy with probability s_a (if they saw A) or s_b (if they saw B). Otherwise they keep their current trait.
Unlike the r-shaped curve of biased mutation (fast start, slow finish), biased transmission produces s-shaped curves: slow-fast-slow. Selection requires variation to act on.
Selection strength depends on s_a minus s_b, not their absolute values. s_a=0.1, s_b=0 behaves like s_a=0.6, s_b=0.5—just with more noise in the latter.
Unlike biased mutation, biased transmission cannot create traits from nothing. If A starts at 0%, it stays at 0%. The favoured trait needs to exist to spread.