Evolutionary psychologists have suggested that stepchildren should be over-represented as victims of lethal parental violence compared with children living with their two genetic parents, because of relatively more lapses in parental solicitude among stepparents. In our study, using data over a period of 35 years in Sweden (1965-1999), there was no overall over-representation of stepchildren as victims. For very young stepchildren there was a tendency for over-representation. In families with both stepchildren and children genetically related to the offender, genetic children tended to be more likely to be victims.
In this retrospective study, relevant demographic, social, and clinical variables were examined in 77 cases of paternal filicide. Between 1991 and 2001, all consecutive coroners' files on domestic homicide in Québec, Canada, were reviewed, and 77 child victims of 60 male parent perpetrators were identified. The results support data indicating that more fathers commit filicide than do mothers. A history of family abuse was characteristic of a substantial number of cases, and most of the cases involved violent means of homicide. Filicide was frequently (60%) followed by the suicide of the perpetrator and more so (86%) in cases involving multiple sibling victims. The abuse of drugs and alcohol was rare. At the time of the offense, most of the perpetrators were suffering from a psychiatric illness, usually depressive disorder. Nearly one-third were in a psychotic state. The proportion of fatal abuse cases was comparatively low. Many of the perpetrators had had contact with health professionals prior to the offense, although none had received treatment for a psychiatric illness.
Evolutionary psychologists have hypothesized, inspired by evolutionary biology, that parents should care less for children with whom they are not genetically related since these young do not contribute to the genetic fitness of the parents. Based on this, evolutionary psychologists have predicted that there will be an overrepresentation of step-parents as offenders in family-related killings of children. Data on child homicide, particularly from Canada, have supported this prediction in that the frequency of children killed was relatively high in families where one of the two parents was a step-parent. Here we present a survey of all child homicide that occurred in Sweden between 1975 and 1995. In contrast to the Canadian data, children in Sweden living in families with a step-parent were not at an increased risk compared with children living together with two parents to whom they were genetically related. In addition, there were no other indications that step-parents are overrepresented as offenders.