text: One study found that slightly altering photographs to resemble the faces of study participants more closely increased the trust the participants expressed regarding depicted persons.Another cue is having the same family name, especially if rare, which has been found to increase helpful behavior.Another study found more cooperative behavior, the greater the number of perceived kin in a group.Using kinship terms in political speeches increased audience agreement with the speaker in one study.This effect was powerful for firstborns, who are typically close to their families.Vested interests.People are likely to suffer if their friends, allies and those from similar social ingroups suffer or disappear.Helping such group members may, therefore, also benefit the altruist.Making ingroup membership more noticeable increases cooperativeness.Extreme self-sacrifice towards the ingroup may be adaptive if a hostile outgroup threatens the entire ingroup.Reciprocal altruism.See also Reciprocity (evolution).Direct reciprocity.Research shows that it can be beneficial to help others if there is a chance that they will reciprocate the help.The effective tit for tat strategy is one game theoretic example.Many people seem to be following a similar strategy by cooperating if and only if others cooperate in return.One consequence is that people are more cooperative with one another if they are more likely to interact again in the future.People tend to be less cooperative if they perceive that the frequency of helpers in the population is lower.They tend to help less if they see non-cooperativeness by others, and this effect tends to be stronger than the opposite effect of seeing cooperative behaviors.Simply changing the cooperative framing of a proposal may increase cooperativeness, such as calling it a "Community Game" instead of a "Wall Street Game".A tendency towards reciprocity implies that people feel obligated to respond if someone helps them.