Indigenous Amazonians such as the Ashaninka tribe in Peru generally have large family units.  According to the Division of Statistics of the Peruvian Ministry of Health, the average indigenous mother has over eight children.  This is in contrast to a Peruvian woman in Lima who on the average has less than two children.  To make matters more complex, an indigenous man, such in the above photograph, can have more than one wife.  Often the women in a polygamous family are biological sisters and therefore, from a genetic and evolutionary viewpoint, each mother has a vested interest in the survival of the other children in the family, even though the children may not be her own.