Does judging people by their group's reputation stabilize cooperation?

People often judge individuals based on their group's reputation rather than tracking everyone's personal history. A new mathematical model shows that when stereotyping targets strategy patterns rather than fixed group labels, it unexpectedly stabilizes eight new cooperation norms alongside the classical leading eight. These hybrid strategies become stable only above a critical stereotyping threshold, suggesting that group-level impressions, even crude ones, can sustain cooperation where individual reputation tracking alone fails.