Sexual jealousy is another cross-cultural human universal,27 giving rise to the phenomenon of mate-guarding.28 A couple out on a date, for example, will often use “tie-signs”—handholding, arm-on-shoulder, and so forth—to signal their romantic connection to their partner. These signals are intended not just for each other, but also for third parties, that is, potential rivals. One research team approached and interviewed couples waiting in line to buy movie tickets and found that men performed more tie-signs with their dates when the interviewer posed a greater romantic threat—when the
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