But most investigations in psychology have focused on interaction with strangers. Evidence of various types shows examples of relationship specific social psychologies. One area that illustrates this is interpersonal conflicts. She has looked at victim-killer patterns of homicides for context, nature and demography. Male sexual jealousy as the number one motive for murder appears to be cross cultural.
Children too are most at risk from unrelated males with whom they live.
In evolutionary terms this makes sense, the male is safe guarding his genetic future by eliminating those who would supplant his own offspring. This does not of course condone such behaviour but does show our mammalian heritage, where such behaviour occurs when a new male takes control. John Tooby proposed that human social life has formed pathways to the evolution of altruism that are alternate to kin selection and reciprocal altruism in explaining human love and friendship. Some distinguishing characteristics of altruism, specifically expecting a pay back, are seen in all cultures as a lack of friendship. He therefore maintains that humans have evolved risky behaviour which damages short term fitness but demonstrates long term commitment.