Social media ranking algorithms typically optimize for users' revealed preferences, i.e. user engagement such as clicks, shares, and likes. Many have hypothesized that by focusing on users' revealed preferences, these algorithms may exacerbate human behavioral biases. In a preregistered algorithmic audit, we found that, relative to a reverse-chronological baseline, Twitter's engagement-based ranking algorithm amplifies emotionally charged, out-group hostile content that users say makes them feel worse about their political out-group. Furthermore, we find that users do