Multi-level Selection Theory

Within any one tribe, altruistic behaviour would be deselected by the dominance of selfish behaviour. However, if altruistic behaviour increased the overall fitness of the group, then the groups with the highest proportion of altruists would outperform the more selfish ones. Under appropriate conditions, this alternative selection pressure could dominate the disadvantage of altruism for the individual. Multi-level selection doesn't only occur on these two levels, since animals may be a part of various groups - close family group, extended family, tribe etc. We can consider evolutionary selection to happen on each level simultaneously.

This explanation of altruism finds more evidence from anthropological studies which support viewing of groups of humans as adaptive units. According to Sober and Wilson,   "the concept of human groups as adaptive units may be supported not only by evolutionary theory but by the bulk of empirical information on human social groups in all cultures around the world."

Although the case for the existance of multi-level selection (MLS) is quite compelling, this does not in itself provide evidence for MLS as an evolutionary mechanism of developing altruism, which is only one of many behaviour patterns that could evolve to increase the survival fitness of groups. Multi-level selection may be supplemented or replaced by other forms of intergroup interaction (e.g. 'Social control') that are more evolutionarily stable. It therefore seems likely that a proper understanding of the relationship between MLS and altruism requires consideration of other mechanisms such as kin selection and reciprocal altruism.