Positive forces that bring persons together, including combinations of behavior and physical features. One such force, at least in adults, is the support offered by another person when one encounters difficulties. Others identified include proximity (geographically including something as seemingly mundane as seating in a classroom), association (e.g., sharing the same opinions), similarity (e.g., in agreement about things in life generally), reciprocal liking (liking those who we feel like us), and physical attractiveness (e.g., others in who we perceive our own physical attractiveness). The latter, which plays a salient role in forming friendships but less so in choosing a mate, has also been shown in a number of studies to be evident in the visual preferences for faces in infants as young as 2 months of age.