An assessment of some proposed exceptions to the phenomenon of nepotistic discrimination against stepchildren

Stepparents commit child abuse and homicide at much higher rates than genetic parents. Proposed exceptions, including a recent claim that there is no such "Cinderella effect" in Swedish homicides, are shown to be mistaken. The hypothesis that only "mothers' boyfriends" abuse children excessively, whereas married stepfathers do not, is tested and rejected in an analysis of Canadian homicides. De facto marriage and steprelationship are confounded, but each is a major risk factor when the other is controlled. Abuse is a rare and presumably non-adaptive manifestation of discrimination, but recent research confirms that stepchildren are more generally disadvantaged with respect to positive investments. There are no known exceptions to the ubiquitous phenomenon of parents discriminating, on average, against stepchildren, but there is cross-national variation in the magnitude of these effects, and the determinants of this variability warrant investigation.