The prominence of reciprocal altruism is a testament to a vervet’s ability to recognize relationships among group members and predict their behavior. Reciprocal altruism is defined as "an exchange of beneficial acts between individuals, in which the benefits to the recipient exceed the cost to the altruist" (Vermeer 1993). Cooperation of this kind can only occur with frequent encounters between individuals. Most cooperative interactions occur between kin, while reciprocity between non-kin is quite rare. Grooming serves to develop a more affinitive relationship between non-kin, increasing their chances of cooperation. While grooming, the groomer removes ectoparasites by picking through the fur of the groomee. In fact, this behavior is considered to be the most common affinitive behavior among non-human primates. Vervets are known to be more likely to support an unrelated individual if he/she has previously behaved affinitively towards the potential supporter. A more dominant individual, for example, will form an alliance with a subordinate, who has groomed her before, against an aggressor who harasses the subordinate. Cooperative behavior of this kind could facilitate the establishment of long-term social bonds from which individuals could benefit from future reciprocal actions (Seyfarth and Cheney 1984). Higher-ranking matrilines receive more non-matrilineal support than other matrilines in the troop. As mentioned previously, high ranking matrilines are considered more valuable as reciprocators for future support in agonistic interaction. This is because the probability of future aid is higher if a high-

Allomothering is another form of cooperation that serves to benefit both mother and allomother. For a mother, reduced time and energy directed towards the rearing of an infant can lead to shorter inter-birth intervals, and thus greater reproductive success. An allomother is defined as an immature individual who is not yet physiologically capable of breeding. An allomother gains valuable maternal experience which readies her for the successful rearing of her first infant. Studies have demonstrated that females experienced in infant handling and caretaking, through allomothering as juveniles, are more likely to effectively raise their first born infant. Allomothering is found to be preferentially directed towards infant siblings and infants of higher-ranking females. The latter individuals are thought to have higher value as associates regarding reciprocal altruism, and are thus

station, but sits alertly, vigilant of any approaching predators. This behavior is termed altruistic since for a male, there is not much relatedness in the group because he is an immigrant. His main objects of protection are his offspring and potential mates in the group. The sentinel's primary purpose is to warn his troop members of impending predator attacks. This is conveyed through a series of visual, rather than vocal cues. His conspicuous position allows for maintaining visual contact with the group. Foragers are warned by reading the sentinel's actions. Vocalizations would alert the approaching predator to the presence of the troop. Refraining from this strategy would decrease the mortality risk of foragers and permit for only a temporary retreat, resuming foraging after the predator has gone. Vocalizations are only used in the cases of a surprise attack or knowledge that the predator has already spotted the troop. In these cases, vocalizations serve to distract the predator while alarming foragers. Visual signals rather than aural signals are the preferred media for these altruistic sentinels (Horrocks 1990).