Cinderella effect  

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The Cinderella effect is a term used by psychologists to describe the high incidence of stepchildren being physically abused, sexually abused, neglected or murdered, or otherwise mistreated at the hands of their stepparents at significantly higher rates than their genetic counterparts. It takes its name from the fairytale character Cinderella, who in the story was cruelly mistreated by her stepmother and stepsisters.


Daly and Wilson research

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.

Unlike the lion, however, humans in a stepparenting situation face a more complicated tradeoff since they cannot completely disown their partner's offspring from a previous relationship, as they would risk losing sexual access to their partner and any chance of producing potential offspring. Thus, according to Daly and Wilson, stepparental investment can be viewed as mating effort to ensure the possibility of future reproduction with the parent of their stepchild. This mating effort hypothesis suggests that humans will tend to invest more in their genetic offspring and invest just enough in their stepchildren. It is from this theoretical framework that Daly and Wilson argue that instances of child abuse towards non-biological offspring should be more frequent than towards biological offspring.

One would therefore expect greater parental responsiveness towards one's own offspring than towards unrelated children, and this will result in more positive outcomes and fewer negative outcomes towards one's own children than towards other children in which one is expected to invest (i.e., stepchildren). "If child abuse is a behavioral response influenced by natural selection, then it is more likely to occur when there are reduced inclusive fitness payoffs owing to uncertain or low relatedness". Owing to these adaptations from natural selection, child abuse is more likely to be committed by stepparents than genetic parents—both are expected to invest heavily in the children, but genetic parents will have greater child-specific parental love that promotes positive caretaking and inhibits maltreatment.

Daly and Wilson report that this parental love can explain why genetic offspring are more immune to lashing out by parents. They assert that, "Child-specific parental love is the emotional mechanism that permits people to tolerate—even to rejoice in—those long years of expensive, unreciprocated parental investment". They point to a study comparing natural father and stepfather families as support for the notion that stepparents do not view their stepchildren the same as their biological children, and likewise, children do not view their stepparents the same as their biological parents. This study, based on a series of questionnaires which were then subjected to statistical analyses, reports that children are less likely to go to their stepfathers for guidance and that stepfathers rate their stepchildren less positively than do natural fathers.

Daly and Wilson's reports on the overrepresentation of stepparents in child homicide and abuse statistics support the evolutionary principle of maximizing one's inclusive fitness, formalized under Hamilton's Rule, which helps to explain why humans will preferentially invest in close kin. Adoption statistics also substantiate this principle, in that non-kin adoptions represent a minority of worldwide adoptions. Research into the high adoption rates of Oceania shows that childlessness is the most common reason for adopting, and that in the eleven populations for which data was available, a large majority of adoptions involved a relative with a coefficient of relatedness greater than or equal to 0.125 (e.g., genetic cousins). It is also observed that parents with both biological and adopted children bias the partitioning of their estates in favor of the biological children, demonstrating again that parental behavior corresponds to the principles of kin selection.


In their 1985 Canadian sample, Daly and Wilson classify the frequencies of different living arrangements (two natural parents, one natural parent, one natural parent with one stepparent, or other) according to child age. This was accomplished by administering a randomized telephone survey.

Records of child abuse from children's aid organizations as well as police reports on runaways and juvenile offenders were then used to determine whether children from stepparental living situations were overrepresented as abuse victims when compared to the demographic data gathered from the telephone survey data. The results indicate that the only living situation that has a significant correlation to increased child abuse is one natural parent and one stepparent in the same household. While rates of running away and crime were comparable for children living with stepparents and children of single-parents, abuse rates for children living with stepparents were much higher.

Daly and Wilson examined several potentially confounding variables in their research, including socioeconomic status, family size, and maternal age at childbirth, however only minor differences between natural-parent and stepparent families with respect to these factors were found, indicating that none of these are major contributing factors to the observed Cinderella effect.

See also

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