Artificial intelligence systems distort upstream selection in human social learning

Humans are social learners who depend on observing others to acquire knowledge, norms, and behaviors, a capacity that underlies cumulative cultural evolution. Social learning unfolds in two stages: upstream selection determines what information becomes visible, and downstream selection determines what learners copy from that visible sample. Downstream selection occurs through biases such as conformity bias (copying what appears common) and prestige bias (copying those who appear highly respected). These downstream biases can be adaptive when upstream selection yields a sample that reflects the population's true distribution, so that what appears common is actually common and those who appear respected are actually competent. We argue that digital technologies disrupt this condition, creating an upstream selection problem. Engagement-based algorithms amplify the tails of the distribution, surfacing rare and extreme content, whereas generative AI collapses it toward the mode (of the population or the user), erasing the surrounding diversity. Crucially, in each system the optimization signal shapes both visibility and prestige. For engagement-based algorithms, the signal is engagement: creators who post extreme content become more visible and, through the likes, shares, and followers, appear more prestigious. For generative AI, the signal is statistical typicality: it makes a modal answer dominant and, with no alternatives shown, makes the model that produced it appear more prestigious. These distortions can give rise to emergent group-level phenomena, including pluralistic ignorance and illusory consensus. Synthesizing evidence across psychology, cultural evolution, and computational social science, we provide a framework for how digital technologies disrupt social learning and outline interventions for restoring functional cultural transmission.