Monkeys live in a complex social nexus and rich foraging habitat, and their social and intellectual skills develop in these arenas. Their tooluse and problem solving abilities put them on a different level from most mammalian clades (Beck, 1980; Antinucci & Visalberghi, 1986; Tomasello & Call, 1997; Parker & McKinney, 1999). Young monkeys must learn how to obtain sustenance, as well as how, when, and with whom they should groom, communicate, and play. They must learn to understand facial and vocal communication, recognize and manage their social bonds of kinship and friendship (even if the social ranks are asymmetric), and manoeuver in the field of their dominance relationships (which are asymmetric except for the highest and lowest ranking) (van Hooff, 1967; Stein, 1981; Fedigan, 1982; Gouzoules, Gouzoules & Marler, 1984; Smuts, 1985; Strum, 1987; Whiten & Byrne, 1988; Cheney & Seyfarth, 1990; King, 1994; Zeller, 1994, 1996).

Given the complexity of their world, the psychological complexity of monkeys is to be expected. When I watch free-ranging monkeys using directional gaze to signal an interest in food or approaching danger, or blocking others' views of a yawn (which could be perceived as a threat), I get the strongest impression that they comprehend the effects of their own actions and act intentionally. Take the following observation: