Cinderella Effect
Encyclopedia
The Cinderella effect is a term used by psychologists to describe the high incidence of stepchildren being physically abused
, emotionally abused
, sexually abused, neglect
ed, murder
ed, or otherwise mistreated at the hands of their stepparents
at significantly higher rates than at the hands of their genetic parents. It takes its name from the fairy tale
character Cinderella
, who in the story was cruelly mistreated by her stepmother and stepsisters.
The effect has been called "one of the poster-children of evolutionary psychology
."
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". Studies have found that not biologically related parents are up to a hundred times more likely to kill a child than biological parents.
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 to 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."
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."
. 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.
s 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 the mother and any chance of fathering 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 mother. This mating effort hypothesis suggests that human males 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 childless
ness 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
.
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.
that the mother would normally form with her own child. This attachment bond must be formed before the age of two in order to become a secure bond, and adoption can often disrupt the development of this bond. An infant must be fed by the primary parental figure, usually the mother, and must have the mother present during severely physically painful events in order for a parental attachment bond to form, and either a consistent omission of the mother from this process or an alteration between two people (the original mother and the adoptive mother) can cause either an insecure attachment or disorganized attachment from the parent to the child. As a result, it is highly recommended by most psychologists that the adoptive mother be present very early in the infants life, preferably immediately after its birth, in order to avoid attachment disruptions and attachment disorders.
. Tooley et al. follow the argument of Daly and Wilson to extend the Cinderella effect from cases of abuse to incidences of unintentional fatalities. Children are not only vulnerable to abuse by their parents, but they are also dependent on their parents for supervision and protection from a variety of other harms. Given that parental supervision is fundamentally correlated to incidences of unintentional childhood injury as shown by Wadsworth et al. and Peterson & Stern, Tooley et al. posit that selective pressures would favor an inclination towards parental vigilance against threats to offspring well-being. Tooley et al. further argue that parental vigilance is not as highly engaged in stepparents as genetic parents, therefore placing stepchildren at greater risk for unintentional injury.
Based on data gathered from the Australia National Coroners’ Information System, stepchildren under five years of age are two to fifteen times more likely to experience an unintentional fatal injury, especially drowning, than genetic children. Additionally, the study finds that the risks of unintentional fatal injury are not significantly higher for genetic children in single parent homes versus two-parent homes. This difference suggests that removing one biological parent from the home does not significantly increase risk to the children, but that adding a nonbiological parent to the home results in a drastic increase in the risk of unintentional fatal injury. Despite the fact that adding a stepparent to the home increases the available resources in terms of supervision in comparison to a single-parent home, risk of unintentional fatal injury still significantly rises. This higher risk of injury for stepchildren can be attributed to the fact that stepparents occupy the same supervisory role as a genetic parent, yet they have a lower intrinsic commitment to protecting the child and therefore are less likely to be adequately vigilant. The authors conclude that the Cinderella effect applies not only to purposeful abuse by stepparents, but is also relevant to explaining increased rates of accidental fatalities among stepchildren.
Furthermore, a study of parental investment behaviors among American men living in Albuquerque, New Mexico
reveals a trend of increasing financial expenditures on genetic offspring in comparison to step-offspring, which also suggests that parents are less inclined to preserve the well-being of stepchildren. The study assesses paternal investment based on four measures: the probability that a child attends college, the probability that the child receives money for college, the total money spent on children, and the amount of time per week spent with children. Four different classifications of father-child relationships are examined and compared, including fathers living with their genetic children and fathers living with the stepchildren of their current mates. Though the study finds a clear trend of increasing investment in genetic children, the data also shows that fathers do still invest substantially in stepchildren. The authors explain the parental investment exhibited by fathers towards stepchildren as possibly motivated by the potential to improve the quality or increase the duration of the man’s relationship with the stepchildren’s mother. This studied corroborates the findings of Lynn White, that stepparents in general provide less social support
to stepchildren than their genetic children.
Though the general trend of the data from this study supports the Cinderella effect, Anderson and colleagues note that the observed differences between parental investment in genetic children and stepchildren might be slightly reduced by a few confounding factors. For example, the authors point out that stepparenting is a self-selective process, and that when all else is equal, men who bond with unrelated children are more likely to become stepfathers, a factor that is likely to be a confounding variable in efforts to study the Cinderella effect. Anderson and colleagues also conducted a similar study of Xhosa students in South Africa
that analyzes the same four classifications of paternal-child relationships, and this study offers similar results to those observed among fathers in Albuquerque.
Additionally, a study of Hadza foragers in Tanzania
by Marlowe also finds evidence of decreased care provided by fathers to stepchildren when compared with genetic children. The author uses the Mann-Whitney U-tests
to evaluate most of the observed differences in care exhibited towards genetic and stepchildren, and finds that Hadza men spend less time with (U=96), communicate less with (U=94.5), nurture less, and never play with their stepchildren. Marlowe further argues that any care that is provided towards stepchildren is likely attributable to the man’s mating efforts and not parental interest in the well-being of the stepchildren.
In further support of the Cinderella effect as elaborated by Daly and Wilson, a study conducted in a rural village in Trinidad
demonstrates that in households containing both genetic children and stepchildren, fathers devote approximately twice as much time to interaction with genetic offspring in comparison to stepchildren. Additionally, this study finds that the duration of the relationship between the stepfather and stepchildren is negatively correlated with the relative proportion of interaction time and positively correlated with the relative proportion of antagonistic interactions between the two. As a proportion of total time spent interacting with genetic and stepchildren, fathers are shown to have approximately 75 percent more antagonistic interactions with stepchildren. In this study, antagonistic interactions are defined as involving physical or verbal combat or an expression of injury. This includes, for example, spanking, screaming, crying, and arguing. The duration of the relationship between genetic fathers and children shows a positive correlation with both relative proportion of interaction time and antagonistic interaction. The author argues that these results show that in terms of time invested, fathers favor genetic children over stepchildren, and this preference is not attributable to the duration of the father-child relationship, a factor which is sometimes believed to be a confounding variable in the Cinderella effect. Though this study does claim a significant increase in antagonistic behavior between stepparents and stepchildren and therefore supports the Cinderella effect, it also notes that only six percent of all the observed parent-child interactions were considered antagonistic, and that the researchers never noticed any blatant physical child abuse.
s rather than “the evolutionary causes of psychological traits.” Buller also posits that the degree of abuse is exaggerated, since Daly and Wilson's 1985 Canadian sample included cases of sexual abuse as well as cases of unintentional omission, such as not buckling a child’s seatbelt in the car. Buller asserts that unintentional omission does not fall under the realm of dangerous acts, and rather should be designated “maltreatment”. He argues that since sexual abuse is not often accompanied by physical abuse, it is not actually a dangerous act committed against the child. Daly and Wilson respond to Buller’s criticism by stating that Buller confuses the empirical statistical findings, which define the Cinderella effect, with the proposed theoretical framework, which offers an evolutionary explanation for the data.
Buller also claims that Daly and Wilson’s findings are inherently biased since they use data from official documents, and the officials collecting that data are trained to take special notice of stepparents versus biological parents. Furthermore, Buller states that since Daly and Wilson rely on official reports (such as death certificates) for their data, and that this data is inherently biased against stepparents. He cites a Colorado
study, in which it was found that maltreatment fatalities were more likely to be correctly reported on death certificates when an unrelated individual was the perpetrator rather than when a parent was the perpetrator, suggesting that the data is empirically skewed to support the Cinderella effect. According to this study, by Crume et al., when the perpetrator of the murder was a parent, maltreatment was correctly noted on the death certificate only 46 percent of the time. Furthermore, they found that when the perpetrator was an “Other unrelated (including boyfriend)” individual, maltreatment was reported on the death certificate 86 percent of the time, significantly higher than for parents. Although these statistics seem to provide evidence of bias against stepparents, further review of the data undermines this conclusion. As Crume et al. and Daly and Wilson note, maltreatment was only likely to be reported on the death certificates 47 percent of the time in the case of “Other relatives (including step-parents),” which represents a marginal increase from the amount of parental maltreatment. Therefore, as Daly and Wilson respond to Buller’s critique, this does not seem to be a significant source of error in studying the Cinderella effect and does not provide evidence for inherent bias in their data.
between 1975 and 1995, which found that children living in households with a non-genetic parent were not at an increased risk of homicide when compared to children living with both genetic parents. The study, published in 2000 and conducted by Temrin and colleagues argued that when Daly and Wilson classified homicides according to family situation, they did not account for the genetic relatedness of the parent who actually committed the crime. In the Swedish sample, in two out of the seven homicides with a genetic and non-genetic parent, the offender was actually the genetic parent and thus these homicides do not support Daly and Wilson’s definition of the Cinderella effect.
Daly and Wilson attribute the contrasting findings of the Swedish study to an analytical oversight. Temrin and colleagues neglect to consider the fact that the proportion of children in living situations with a stepparent is not constant for all child age groups, but rather increases with age. After correcting for age differences, the Swedish data set produces results in accordance with the previous findings of Daly and Wilson. The Swedish sample does show, however, decreased risk to children living with a stepparent than do the North American samples collected by Daly and Wilson, suggesting that there is some degree of cross-cultural variation in the Cinderella effect.
Burgess and Drais propose that child maltreatment is too complex to be explained fully by genetic relatedness alone and cite other reasons for child maltreatment, such as social factors, ecological factors and child traits such as disability and age. However, they also note that these traits are simply indicative, and do not inevitably lead to child maltreatment. Temrin and colleagues also suggest that there may be other factors involved with child homicide, such as prior convictions, drug abuse problems, lost custody battles and mental health problems.
In 1984, Giles-Sims and David Finkelhor
categorized and evaluated five possible hypotheses that could explain the Cinderella effect: “social-evolutionary theory,” “normative theory,” “stress theory,” “selection factors” and “resource theory”. The social-evolutionary theory is based on the proposal that non-genetically related parents will invest less in costly parental duties, due to the fact that their genes are not being passed on by that individual. The normative theory proposes that, due to genetic repercussions, incest among genetically related individuals is a widespread taboo and would thus be less common among biological relatives. They propose that incest among stepfamilies would be less taboo, since there is no risk of genetic degradation. The stress theory proposes that increased stressors, which are inherently more common among stepfamilies, cause an increased risk of abuse. The selection factors theory proposes that individuals who are likely to be stepparents (divorcees) are likely to be inherently more violent due to emotional disturbances, aggressive impulses, and self-esteem issues. Due to this, stepparents as a group would have a higher proportion of individuals with violent-prone characteristics, which would suggest that the abuse is happening due to personality factors, rather than the stepparental relationship directly. Finally, according to resource theory, individuals who contribute resources are granted authority, while individuals that lack resources are denied authority and more likely to resort to violence to obtain authority. It is therefore hypothesized that stepparents who are able to contribute resources to a family and have those resources be accepted by the family are less likely to be abusive. However, this hypothesis had yet to be tested directly on stepfamilies. This paper of Giles-Sims and Finkelhor predates however practically all empirical studies on the Cinderella effect.
Physical abuse
Physical abuse is abuse involving contact intended to cause feelings of intimidation, injury, or other physical suffering or bodily harm.-Forms of physical abuse:*Striking*Punching*Belting*Pushing, pulling*Slapping*Whipping*Striking with an object...
, emotionally abused
Psychological abuse
Psychological abuse, also referred to as emotional abuse or mental abuse, is a form of abuse characterized by a person subjecting or exposing another to behavior that may result in psychological trauma, including anxiety, chronic depression, or post-traumatic stress disorder...
, sexually abused, neglect
Neglect
Neglect is a passive form of abuse in which a perpetrator is responsible to provide care for a victim who is unable to care for himself or herself, but fails to provide adequate care....
ed, murder
Murder
Murder is the unlawful killing, with malice aforethought, of another human being, and generally this state of mind distinguishes murder from other forms of unlawful homicide...
ed, or otherwise mistreated at the hands of their stepparents
Stepfamily
A stepfamily, also known as a blended family or reconstituted family, is a family in which one or both members of the couple have children from a previous relationship...
at significantly higher rates than at the hands of their genetic parents. It takes its name from the fairy tale
Fairy tale
A fairy tale is a type of short story that typically features such folkloric characters, such as fairies, goblins, elves, trolls, dwarves, giants or gnomes, and usually magic or enchantments. However, only a small number of the stories refer to fairies...
character Cinderella
Cinderella
"Cinderella; or, The Little Glass Slipper" is a folk tale embodying a myth-element of unjust oppression/triumphant reward. Thousands of variants are known throughout the world. The title character is a young woman living in unfortunate circumstances that are suddenly changed to remarkable fortune...
, who in the story was cruelly mistreated by her stepmother and stepsisters.
The effect has been called "one of the poster-children of evolutionary psychology
Evolutionary psychology
Evolutionary psychology is an approach in the social and natural sciences that examines psychological traits such as memory, perception, and language from a modern evolutionary perspective. It seeks to identify which human psychological traits are evolved adaptations, that is, the functional...
."
Background
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
Child abuse
Child abuse is the physical, sexual, emotional mistreatment, or neglect of a child. In the United States, the Centers for Disease Control and Prevention and the Department of Children And Families define child maltreatment as any act or series of acts of commission or omission by a parent or...
and homicide
Homicide
Homicide refers to the act of a human killing another human. Murder, for example, is a type of homicide. It can also describe a person who has committed such an act, though this use is rare in modern English...
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
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, Great Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
, and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
indeed incur greatly elevated risk of child maltreatment of various sorts, especially lethal beatings". Studies have found that not biologically related parents are up to a hundred times more likely to kill a child than biological parents.
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 to 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 psychology theory
Evolutionary psychologistsEvolutionary psychology
Evolutionary psychology is an approach in the social and natural sciences that examines psychological traits such as memory, perception, and language from a modern evolutionary perspective. It seeks to identify which human psychological traits are evolved adaptations, that is, the functional...
Martin Daly
Martin Daly
Martin Daly is a Professor of Psychology at McMaster University in Hamilton, Ontario, Canada and author of many influential papers on evolutionary psychology. Current research topics include an evolutionary perspective on risk-taking and interpersonal violence, especially male-male conflict and...
and Margo Wilson
Margo Wilson
Margo Wilson was Professor of Psychology at McMaster University in Hamilton, Ontario, Canada. Along with her husband and frequent research partner Martin Daly, she wrote many influential papers and books in the field of evolutionary psychology...
propose that the Cinderella effect is a direct consequence of the modern evolutionary
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
theory of inclusive fitness
Inclusive fitness
In evolutionary biology and evolutionary psychology, the inclusive fitness of an organism is the sum of its classical fitness and the number of equivalents of its own offspring it can add to the population by supporting others...
, especially parental investment theory
Parental investment
In evolutionary biology, parental investment is any parental expenditure that benefits one offspring at a cost to parents' ability to invest in other components of fitness...
. 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."
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 UniversityMcMaster University
McMaster University is a public research university whose main campus is located in Hamilton, Ontario, Canada. The main campus is located on of land in the residential neighbourhood of Westdale, adjacent to Hamilton's Royal Botanical Gardens...
. Their first measure of the validity of the Cinderella effect was based on data from the American Humane Association
American Humane Association
The American Humane Association is an organization founded in 1877 dedicated to the welfare of animals and children.The AHA's Film and Television Unit has monitored the welfare of animals during the production of films and television programs since 1940. They are the source of the familiar...
(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.
Explanation
All organisms face trade-offTrade-off
A trade-off is a situation that involves losing one quality or aspect of something in return for gaining another quality or aspect...
s as to how to invest their time, energy, risk, and other resources, so investment in one domain (e.g. parental investment
Parental investment
In evolutionary biology, parental investment is any parental expenditure that benefits one offspring at a cost to parents' ability to invest in other components of fitness...
) generally takes away from their ability to invest in other domains (e.g. mating effort
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
, 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
Infanticide
Infanticide or infant homicide is the killing of a human infant. Neonaticide, a killing within 24 hours of a baby's birth, is most commonly done by the mother.In many past societies, certain forms of infanticide were considered permissible...
is an extreme form of biasing parental investment that is widely practiced in the animal world. For example, when an immigrant male lion
Lion
The lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...
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
Competition (biology)
Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...
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 the mother and any chance of fathering 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 mother. This mating effort hypothesis suggests that human males 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
Inclusive fitness
In evolutionary biology and evolutionary psychology, the inclusive fitness of an organism is the sum of its classical fitness and the number of equivalents of its own offspring it can add to the population by supporting others...
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
Child murder
The murder of children is considered an abhorrent crime in much of the world; they are perceived within their communities and the state at large as being vulnerable, and therefore especially susceptible to abduction and murder. The protection of children from abuse and possible death often involves...
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
Adoption
Adoption is a process whereby a person assumes the parenting for another and, in so doing, permanently transfers all rights and responsibilities from the original parent or parents...
statistics also substantiate this principle, in that non-kin adoptions represent a minority of worldwide adoptions. Research into the high adoption rates of Oceania
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...
shows that childless
Childless
Childlessness describes a person who does not have any children. The causes of childlessness are many and it has great personal, social and political significance...
ness 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
Coefficient of relationship
In population genetics, Sewall Wright's coefficient of relationship or coefficient of relatedness or relatedness or r is defined as 2 times the Coefficient of Inbreeding...
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
Kin selection
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...
.
Methods
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
Confounding
In statistics, a confounding variable is an extraneous variable in a statistical model that correlates with both the dependent variable and the independent variable...
in their research, including socioeconomic status
Socioeconomic status
Socioeconomic status is an economic and sociological combined total measure of a person's work experience and of an individual's or family’s economic and social position in relation to others, based on income, education, and occupation...
, 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.
Attachment theory
Evolutionary psychologists have also suggested that one of the causes of stepchild abuse may be the lack of a parental attachment bondAttachment theory
Attachment theory describes the dynamics of long-term relationships between humans. Its most important tenet is that an infant needs to develop a relationship with at least one primary caregiver for social and emotional development to occur normally. Attachment theory is an interdisciplinary study...
that the mother would normally form with her own child. This attachment bond must be formed before the age of two in order to become a secure bond, and adoption can often disrupt the development of this bond. An infant must be fed by the primary parental figure, usually the mother, and must have the mother present during severely physically painful events in order for a parental attachment bond to form, and either a consistent omission of the mother from this process or an alteration between two people (the original mother and the adoptive mother) can cause either an insecure attachment or disorganized attachment from the parent to the child. As a result, it is highly recommended by most psychologists that the adoptive mother be present very early in the infants life, preferably immediately after its birth, in order to avoid attachment disruptions and attachment disorders.
Misunderstandings
It is sometimes argued that this evolutionary psychological account does not explain why the majority of stepparents do not abuse their partners' children, or why a significant minority of genetic parents do abuse their own offspring. However, their argument is based on a misunderstanding: the evolutionary psychological account is that (all else equal) parents will love their own children more than other people's children – it does not argue that stepparents will "want" to abuse their partner's children, or that genetic parenthood is absolute proof against abuse. Under this account, stepparental care is seen as "mating effort" towards the genetic parent, such that most interactions between stepparent and stepchildren will be generally positive or at least neutral, just usually not as positive as interactions between the genetic parent and the child would be.Supportive evidence
Strong support for the Cinderella effect as described by Daly and Wilson comes from a study of unintentional childhood fatal injuries in AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. Tooley et al. follow the argument of Daly and Wilson to extend the Cinderella effect from cases of abuse to incidences of unintentional fatalities. Children are not only vulnerable to abuse by their parents, but they are also dependent on their parents for supervision and protection from a variety of other harms. Given that parental supervision is fundamentally correlated to incidences of unintentional childhood injury as shown by Wadsworth et al. and Peterson & Stern, Tooley et al. posit that selective pressures would favor an inclination towards parental vigilance against threats to offspring well-being. Tooley et al. further argue that parental vigilance is not as highly engaged in stepparents as genetic parents, therefore placing stepchildren at greater risk for unintentional injury.
Based on data gathered from the Australia National Coroners’ Information System, stepchildren under five years of age are two to fifteen times more likely to experience an unintentional fatal injury, especially drowning, than genetic children. Additionally, the study finds that the risks of unintentional fatal injury are not significantly higher for genetic children in single parent homes versus two-parent homes. This difference suggests that removing one biological parent from the home does not significantly increase risk to the children, but that adding a nonbiological parent to the home results in a drastic increase in the risk of unintentional fatal injury. Despite the fact that adding a stepparent to the home increases the available resources in terms of supervision in comparison to a single-parent home, risk of unintentional fatal injury still significantly rises. This higher risk of injury for stepchildren can be attributed to the fact that stepparents occupy the same supervisory role as a genetic parent, yet they have a lower intrinsic commitment to protecting the child and therefore are less likely to be adequately vigilant. The authors conclude that the Cinderella effect applies not only to purposeful abuse by stepparents, but is also relevant to explaining increased rates of accidental fatalities among stepchildren.
Furthermore, a study of parental investment behaviors among American men living in Albuquerque, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
reveals a trend of increasing financial expenditures on genetic offspring in comparison to step-offspring, which also suggests that parents are less inclined to preserve the well-being of stepchildren. The study assesses paternal investment based on four measures: the probability that a child attends college, the probability that the child receives money for college, the total money spent on children, and the amount of time per week spent with children. Four different classifications of father-child relationships are examined and compared, including fathers living with their genetic children and fathers living with the stepchildren of their current mates. Though the study finds a clear trend of increasing investment in genetic children, the data also shows that fathers do still invest substantially in stepchildren. The authors explain the parental investment exhibited by fathers towards stepchildren as possibly motivated by the potential to improve the quality or increase the duration of the man’s relationship with the stepchildren’s mother. This studied corroborates the findings of Lynn White, that stepparents in general provide less social support
Social support
Social support can be defined and measured in many ways. It can loosely be defined as feeling that one is cared for by and has assistance available from other people and that one is part of a supportive social network...
to stepchildren than their genetic children.
Though the general trend of the data from this study supports the Cinderella effect, Anderson and colleagues note that the observed differences between parental investment in genetic children and stepchildren might be slightly reduced by a few confounding factors. For example, the authors point out that stepparenting is a self-selective process, and that when all else is equal, men who bond with unrelated children are more likely to become stepfathers, a factor that is likely to be a confounding variable in efforts to study the Cinderella effect. Anderson and colleagues also conducted a similar study of Xhosa students in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
that analyzes the same four classifications of paternal-child relationships, and this study offers similar results to those observed among fathers in Albuquerque.
Additionally, a study of Hadza foragers in Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
by Marlowe also finds evidence of decreased care provided by fathers to stepchildren when compared with genetic children. The author uses the Mann-Whitney U-tests
Mann-Whitney U
In statistics, the Mann–Whitney U test is a non-parametric statistical hypothesis test for assessing whether one of two samples of independent observations tends to have larger values than the other. It is one of the most well-known non-parametric significance tests...
to evaluate most of the observed differences in care exhibited towards genetic and stepchildren, and finds that Hadza men spend less time with (U=96), communicate less with (U=94.5), nurture less, and never play with their stepchildren. Marlowe further argues that any care that is provided towards stepchildren is likely attributable to the man’s mating efforts and not parental interest in the well-being of the stepchildren.
In further support of the Cinderella effect as elaborated by Daly and Wilson, a study conducted in a rural village in Trinidad
Trinidad
Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...
demonstrates that in households containing both genetic children and stepchildren, fathers devote approximately twice as much time to interaction with genetic offspring in comparison to stepchildren. Additionally, this study finds that the duration of the relationship between the stepfather and stepchildren is negatively correlated with the relative proportion of interaction time and positively correlated with the relative proportion of antagonistic interactions between the two. As a proportion of total time spent interacting with genetic and stepchildren, fathers are shown to have approximately 75 percent more antagonistic interactions with stepchildren. In this study, antagonistic interactions are defined as involving physical or verbal combat or an expression of injury. This includes, for example, spanking, screaming, crying, and arguing. The duration of the relationship between genetic fathers and children shows a positive correlation with both relative proportion of interaction time and antagonistic interaction. The author argues that these results show that in terms of time invested, fathers favor genetic children over stepchildren, and this preference is not attributable to the duration of the father-child relationship, a factor which is sometimes believed to be a confounding variable in the Cinderella effect. Though this study does claim a significant increase in antagonistic behavior between stepparents and stepchildren and therefore supports the Cinderella effect, it also notes that only six percent of all the observed parent-child interactions were considered antagonistic, and that the researchers never noticed any blatant physical child abuse.
David Buller
Philosopher of science David Buller, who dismisses evolutionary biology in general, argues that evolutionary psychology (EP) mistakenly attempts to discover human psychological adaptationPsychological adaptation
A psychological adaptation, also called an Evolved psychological mechanism or EPM, is an aspect of a human or other animal's psychology that is the result of evolutionary pressures. It could serve a specific purpose, have served a purpose in the past , or be a side-effect of another EPM...
s rather than “the evolutionary causes of psychological traits.” Buller also posits that the degree of abuse is exaggerated, since Daly and Wilson's 1985 Canadian sample included cases of sexual abuse as well as cases of unintentional omission, such as not buckling a child’s seatbelt in the car. Buller asserts that unintentional omission does not fall under the realm of dangerous acts, and rather should be designated “maltreatment”. He argues that since sexual abuse is not often accompanied by physical abuse, it is not actually a dangerous act committed against the child. Daly and Wilson respond to Buller’s criticism by stating that Buller confuses the empirical statistical findings, which define the Cinderella effect, with the proposed theoretical framework, which offers an evolutionary explanation for the data.
Buller also claims that Daly and Wilson’s findings are inherently biased since they use data from official documents, and the officials collecting that data are trained to take special notice of stepparents versus biological parents. Furthermore, Buller states that since Daly and Wilson rely on official reports (such as death certificates) for their data, and that this data is inherently biased against stepparents. He cites a Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
study, in which it was found that maltreatment fatalities were more likely to be correctly reported on death certificates when an unrelated individual was the perpetrator rather than when a parent was the perpetrator, suggesting that the data is empirically skewed to support the Cinderella effect. According to this study, by Crume et al., when the perpetrator of the murder was a parent, maltreatment was correctly noted on the death certificate only 46 percent of the time. Furthermore, they found that when the perpetrator was an “Other unrelated (including boyfriend)” individual, maltreatment was reported on the death certificate 86 percent of the time, significantly higher than for parents. Although these statistics seem to provide evidence of bias against stepparents, further review of the data undermines this conclusion. As Crume et al. and Daly and Wilson note, maltreatment was only likely to be reported on the death certificates 47 percent of the time in the case of “Other relatives (including step-parents),” which represents a marginal increase from the amount of parental maltreatment. Therefore, as Daly and Wilson respond to Buller’s critique, this does not seem to be a significant source of error in studying the Cinderella effect and does not provide evidence for inherent bias in their data.
Temrin et al. Sweden study
The findings of Daly and Wilson have been called into question by one study of child homicides in SwedenSweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
between 1975 and 1995, which found that children living in households with a non-genetic parent were not at an increased risk of homicide when compared to children living with both genetic parents. The study, published in 2000 and conducted by Temrin and colleagues argued that when Daly and Wilson classified homicides according to family situation, they did not account for the genetic relatedness of the parent who actually committed the crime. In the Swedish sample, in two out of the seven homicides with a genetic and non-genetic parent, the offender was actually the genetic parent and thus these homicides do not support Daly and Wilson’s definition of the Cinderella effect.
Daly and Wilson attribute the contrasting findings of the Swedish study to an analytical oversight. Temrin and colleagues neglect to consider the fact that the proportion of children in living situations with a stepparent is not constant for all child age groups, but rather increases with age. After correcting for age differences, the Swedish data set produces results in accordance with the previous findings of Daly and Wilson. The Swedish sample does show, however, decreased risk to children living with a stepparent than do the North American samples collected by Daly and Wilson, suggesting that there is some degree of cross-cultural variation in the Cinderella effect.
Alternative hypotheses
It has been noted by multiple researchers that child abuse is an intricate issue and is affected by other factors. Daly and Wilson state, however, that even if evolutionary psychology cannot account for every instance of stepparental abuse, this does not invalidate their empirical findings.Burgess and Drais propose that child maltreatment is too complex to be explained fully by genetic relatedness alone and cite other reasons for child maltreatment, such as social factors, ecological factors and child traits such as disability and age. However, they also note that these traits are simply indicative, and do not inevitably lead to child maltreatment. Temrin and colleagues also suggest that there may be other factors involved with child homicide, such as prior convictions, drug abuse problems, lost custody battles and mental health problems.
In 1984, Giles-Sims and David Finkelhor
David Finkelhor
David Finkelhor is an American sociologist known for his research into child sexual abuse and related topics. He is the director of Crimes against Children Research Center, Co-Director of the and Professor of Sociology at the University of New Hampshire in the US, from which he received his Ph.D....
categorized and evaluated five possible hypotheses that could explain the Cinderella effect: “social-evolutionary theory,” “normative theory,” “stress theory,” “selection factors” and “resource theory”. The social-evolutionary theory is based on the proposal that non-genetically related parents will invest less in costly parental duties, due to the fact that their genes are not being passed on by that individual. The normative theory proposes that, due to genetic repercussions, incest among genetically related individuals is a widespread taboo and would thus be less common among biological relatives. They propose that incest among stepfamilies would be less taboo, since there is no risk of genetic degradation. The stress theory proposes that increased stressors, which are inherently more common among stepfamilies, cause an increased risk of abuse. The selection factors theory proposes that individuals who are likely to be stepparents (divorcees) are likely to be inherently more violent due to emotional disturbances, aggressive impulses, and self-esteem issues. Due to this, stepparents as a group would have a higher proportion of individuals with violent-prone characteristics, which would suggest that the abuse is happening due to personality factors, rather than the stepparental relationship directly. Finally, according to resource theory, individuals who contribute resources are granted authority, while individuals that lack resources are denied authority and more likely to resort to violence to obtain authority. It is therefore hypothesized that stepparents who are able to contribute resources to a family and have those resources be accepted by the family are less likely to be abusive. However, this hypothesis had yet to be tested directly on stepfamilies. This paper of Giles-Sims and Finkelhor predates however practically all empirical studies on the Cinderella effect.
Ethical issues
Discussing the implications of this line of research, Australian psychologist Greg Tooley, author of a 2006 study confirming the existence of the effect, confessed that "It is certainly difficult to talk about because it is such a hot issue."Conclusion
Daly and Wilson, whose findings have been corroborated by a number of independent studies, have contributed to an ever-growing body of work related to the Cinderella effect. Of the researchers in disagreement with Daly and Wilson, some have a well-known skepticism of the field of evolutionary psychology, such as David Buller, while others have put forth studies that suffer from analytical error, such as Hans Temrin. While there are other hypotheses that attempt to debunk the Cinderella effect, or explain it in non-evolutionary terms, they remain largely untested and are unlikely to be able to fully account for the striking variation between genetic and stepparental instances of child maltreatment.See also
- ParentingParentingParenting is the process of promoting and supporting the physical, emotional, social, and intellectual development of a child from infancy to adulthood...
- Parental investmentParental investmentIn evolutionary biology, parental investment is any parental expenditure that benefits one offspring at a cost to parents' ability to invest in other components of fitness...
theory - FamilyFamilyIn human context, a family is a group of people affiliated by consanguinity, affinity, or co-residence. In most societies it is the principal institution for the socialization of children...
- Paternal bondPaternal bondA paternal bond refers to the relationship between a father and his child. In the U.S., legal paternity is presumed for the husband of the mother unless a separate action is taken; an unmarried man may establish paternity by signing a voluntary recognition of paternity or by taking court action...
- Maternal bondMaternal bondThe maternal bond is typically the relationship between a mother and her child.While it typically occurs due to pregnancy and childbirth, it may also occur between a woman and an unrelated child, such as in adoption...
- Nuclear familyNuclear familyNuclear family is a term used to define a family group consisting of a father and mother and their children. This is in contrast to the smaller single-parent family, and to the larger extended family. Nuclear families typically center on a married couple, but not always; the nuclear family may have...
- Cinderella complexCinderella complexThe Cinderella complex was first described by Colette Dowling, who wrote a book on women's fear of independence, as an unconscious desire to be taken care of by others...
- The WAVE Trust
Further reading
- Nigel Barber (June 1, 2009)Do parents favor natural children over adopted ones?, The Human Beast blog on Psychology TodayPsychology TodayPsychology Today is a bi-monthly magazine published in the United States. It is a psychology-based magazine about relationships, health, and related topics written for a mass audience of non-psychologists. Psychology Today was founded in 1967 and features articles on such topics as love,...
discussing the following - Mindelle Jacobs (July 4, 2010) The Cinderella effect is not just a fairy tale, Edmonton SunEdmonton SunThe Edmonton Sun is a daily newspaper published in Edmonton, Alberta, Canada. It is a division of Sun Media, a Quebecor company.It began publishing in 1978 and shares many characteristics typical of Sun Media tabloids, including an emphasis on local news stories, its conservative editorial stance,...