Cinderella effect

In evolutionary psychology, the Cinderella effect is the phenomenon of higher incidence of different forms of child-abuse and mistreatment by stepparents than by biological parents. It takes its name from the fairy tale character Cinderella. Evolutionary psychologists describe the effect as a byproduct of a bias towards kin, and a conflict between reproductive partners of investing in young that are unrelated to one partner. There is both supporting evidence for this theory and criticism against it. In evolutionary psychology, the Cinderella effect is the phenomenon of higher incidence of different forms of child-abuse and mistreatment by stepparents than by biological parents. It takes its name from the fairy tale character Cinderella. Evolutionary psychologists describe the effect as a byproduct of a bias towards kin, and a conflict between reproductive partners of investing in young that are unrelated to one partner. There is both supporting evidence for this theory and criticism against it. In the early 1970s, a theory arose on the connection between stepparents and child maltreatment. 'In 1973, forensic psychiatrist P. D. Scott summarized information on a sample of 'fatal battered-baby cases' perpetrated in anger ... 15 of the 29 killers – 52% – were stepfathers.' Although initially there was no analysis of this raw data, empirical evidence has since been collected on what is now called the Cinderella effect through official records, reports, and census. For over 30 years, data has been collected regarding the validity of the Cinderella effect, with a wealth of evidence indicating a direct relationship between step-relationships and abuse. This evidence of child abuse and homicide comes from a variety of sources including official reports of child abuse, clinical data, victim reports, and official homicide data. Studies have concluded that 'stepchildren in Canada, Great Britain, and the United States indeed incur greatly elevated risk of child maltreatment of various sorts, especially lethal beatings'. Powerful evidence in support of the Cinderella effect comes from the finding that when abusive parents have both step and genetic children, they generally spare their genetic children. In such families, stepchildren were exclusively targeted 9 out of 10 times in one study and in 19 of 22 in another. In addition to displaying higher rates of negative behaviors (e.g., abuse) toward stepchildren, stepparents display fewer positive behaviors toward stepchildren than do the genetic parents. For example, on average, stepparents invest less in education, play with stepchildren less, take stepchildren to the doctor less, etc. This discrimination against stepchildren is unusual compared with abuse statistics involving the overall population given 'the following additional facts: (1) when child abuse is detected, it is often found that all the children in the home have been victimized; and (2) stepchildren are almost always the eldest children in the home, whereas the general ... tendency in families of uniform parentage is for the youngest to be most frequent victims.' Evolutionary psychologists Martin Daly and Margo Wilson propose that the Cinderella effect is a direct consequence of the modern evolutionary theory of inclusive fitness, especially parental investment theory. They argue that human child rearing is so prolonged and costly that 'a parental psychology shaped by natural selection is unlikely to be indiscriminate'. According to them, 'research concerning animal social behaviour provide a rationale for expecting parents to be discriminative in their care and affection, and more specifically, to discriminate in favour of their own young'. Inclusive fitness theory proposes a selective criterion for the evolution of social traits, where social behavior that is costly to an individual organism can nevertheless emerge when there is a statistical likelihood that significant benefits of that social behavior accrue to (the survival and reproduction of) other organisms whom also carry the social trait (most straightforwardly, accrue to close genetic relatives). Under such conditions, a net overall increase in reproduction of the social trait in future generations can result. The initial presentation of inclusive fitness theory (in the mid 1960s) focused on making the mathematical case for the possibility of social evolution, but also speculated about possible mechanisms whereby a social trait could effectively achieve this necessary statistical correlation between its likely bearers. Two possibilities were considered: One that a social trait might reliably operate straightforwardly via social context in species where genetic relatives are usually concentrated in a local home area where they were born ('viscous populations'); The other, that genetic detection mechanisms ('supergenes') might emerge that go beyond statistical correlations, and reliably detect actual genetic relatedness between the social actors using direct 'kin recognition'. The relative place of these two broad types of social mechanisms has been debated (see Kin selection and Kin recognition), but many biologists consider 'kin recognition' to be an important possible mechanism. Martin Daly and Margo Wilson follow this second mechanism, and expect that parents 'discriminate in favour of their own young', i.e. their actual genetic relatives. The most abundant data on stepchild mistreatment has been collected and interpreted by psychologists Martin Daly and Margo Wilson, who study with an emphasis in Neuroscience and Behavior at McMaster University. Their first measure of the validity of the Cinderella effect was based on data from the American Humane Association (AHA), an archive of child abuse reports in the United States holding over twenty thousand reports. These records led Wilson and Daly to conclude that 'a child under three years of age who lived with one genetic parent and one stepparent in the United States in 1976 was about seven times more likely to become a validated child-abuse case in the records than one who dwelt with two genetic parents'. Their overall findings demonstrate that children residing with stepparents have a higher risk of abuse even when other factors are considered. All organisms face trade-offs as to how to invest their time, energy, risk, and other resources, so investment in one domain (e.g., parental investment) generally takes away from their ability to invest in other domains (e.g. mating effort, growth, or investment in other offspring). Investment in non-genetic children therefore reduces an individual's ability to invest in itself or its genetic children, without directly bringing reproductive benefits. Thus, from an evolutionary biology perspective, one would not expect organisms to regularly and deliberately care for unrelated offspring. Daly and Wilson point out that infanticide is an extreme form of biasing parental investment that is widely practiced in the animal world. For example, when an immigrant male lion enters a pride, it is not uncommon for him to kill the cubs fathered by other males. Since the pride can only provide support for a limited number of cubs to survive to adulthood, the killing of the cubs in competition with the new male's potential offspring increases the chances of his progeny surviving to maturity. In addition, the act of infanticide speeds the return to sexual receptivity in the females, allowing for the male to father his own offspring in a timelier manner. These observations indicate that in the animal world, males employ certain measures in order to ensure that parental investment is geared specifically toward their own offspring.