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==Research and Studies on the Cinderella Effect==
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In [[evolutionary psychology]], the '''Cinderella effect''' is the alleged higher incidence of different forms of [[child-abuse]] and mistreatment by [[Stepfamily|stepparents]] than by biological parents. It takes its name from the fairy tale character Cinderella. Evolutionary psychologists describe the effect as a remnant of an adaptive [[reproductive strategy]] among [[primate]]s where males frequently kill the offspring of other males in order to bring their mothers into [[estrus]], and give the male a chance to fertilize her himself. There is both supporting evidence for this theory and criticisms against it.
In the early 1970’s, a theory arose on the connection between stepparents and child maltreatment. “In 1973, forensic psychiatrist P. D. Scott had summarized information on a sample of ‘fatal battered-baby cases’ perpetrated in anger (…) fifteen of the twenty-nine killers – fifty-two per cent – were stepfathers.” (“Truth” 33) 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. Years of research have confirmed the hypothesis that stepchildren are significantly more likely to be abused in terms “from baby batterings (''sic'') to sexual molestation of older children” to murder.(“Truth” 30) 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”. (“Assessment” 288)
 
 
For over thirty years, data has been collected regarding the validity of the Cinderella Effect with all the evidence proving a direct relationship between step-relationships and abuse. All such evidence on child abuse and homicide “is derived entirely from official reports of child abuse or from clinical data.” (Gelles and Harrop 79) In Chicago, police homicide records show that “115 children under 5 years of age were killed by their putative fathers in 1965 through 1990, while 63 were killed by stepfathers (…) and because very few babies reside with substitute fathers, the numbers imply greatly elevated risk to such children.” (“Violence” 78) The most powerful evidence in support of the Cinderella Effect is the proof that when abusive parents have both step and genetic children, they generally spare their own children. In such families, stepchildren were exclusively targeted 9 out of 10 times in one study and in 19 of 22 in another.(“Cinderella” 5) This discrimination towards stepchildren is unusual due to “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.” (“Assessment” 288) The Cinderella Effect explains this discrimination of abuse among stepchildren.
 
   
==Studies and Their Findings by Martin Daly and Margo Wilson==
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==Background==
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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."<ref name=TAC33>Daly & Wilson (1999), p. 33</ref> 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.
   
The most profound data on the idea of 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. (“Truth” 26) These records led Wilson and Daly to conclude that “a child under three years of age who lived with one genetic parent and one step-parent in the United States in 1976 was about seven times more likely (…) to become a validated child-abuse case in the AHA records than one who dwelt with two genetic parents.”(“Truth” 27) Records in Great Britain were also examined and found that children were beat by stepfathers at a rate of 100 times more than genetic fathers. (“Cinderella” 2) Overall, their findings prove that children residing with stepparents had a higher risk of abuse even when socio-economic factors were considered.
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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.<ref name=DalyWilson2007>Daly & Wilson (2007) [http://psych.mcmaster.ca/dalywilson/Cinderella_Effect.pdf Is the "Cinderella Effect" controversial?] In Crawford & Krebs (Eds) Foundations of Evolutionary Psychology, pp. 383-400. Mahwah, NJ: Erlbaum.</ref> 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".<ref name="DalyWilson2001">{{cite journal|last=Daly|first=M.|coauthors=M. Wilson|title=An assessment of some proposed exceptions to the phenomenon of nepotistic discrimination against stepchildren|journal=Annales Zoologici Fennici|year=2001|volume=38|pages=287–296|url=ftp://psyftp.mcmaster.ca/dalywilson/Papers/ZoologicaFennica/daly.pdf}}</ref> Studies have found that not biologically related parents are up to a hundred times more likely to kill a child than biological parents.<ref name=Roach2011>{{cite doi|10.4236/psych.2011.24062}}</ref>
   
==Explanations for the Cinderella Effect ==
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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.<ref name="Crawford2008p387">Crawford (2008), p. 387</ref> 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.<ref name="Crawford2008p388">Crawford (2008), p. 388</ref> 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."<ref name="DalyWilson2001" />
   
The Cinderella Effect is best explained through [[evolutionary psychology]]. Its origin and evolution into the role of human behaviors is a direct effect of the Darwinian theory of natural selection as explained by Daly and Wilson. According to theory, “research concerning animal social behaviour (''sic'') provide a rationale for expecting parents to be discriminative in their care and affection, and more specifically, to discriminate in favour (''sic'')of their own young”. (“Truth” 8) Natural selection measures an organisms success by its reproductive ability, explaining why parents invest their resources in their genetic children. This evolved rationale is why parents have developed the desire to protect their own young for investment in their own fitness and to ensure “genetic posterity (inclusive fitness)”. (“Truth” 39)
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==Evolutionary psychology theory==
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{{See also|Infanticide (zoology)|Kin selection}}
As an evolved species, humans follow “the assumption that any evolutionarily successful organism must balance its allocation of time, energy, risk, and other resources to itself-its own growth and maintenance.” (Burgess and Drais 374) Therefore, in the position of step parent, one cannot be expected to care for their non-genetic children out of altruism because they are earning no reproductive benefits. “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.” (Burgess and Drais 376) Due to these adaptations from natural selection, child abuse is more likely to be committed by step-parents than genetic parents.
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==Studies Refuting the Cinderella Effect==
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[[Evolutionary psychology|Evolutionary psychologists]] [[Martin Daly]] and [[Margo Wilson]] propose that the Cinderella effect is a direct consequence of the [[Evolution|modern evolutionary]] theory of [[inclusive fitness]], especially [[Parental investment|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".<ref name="DalyWilson1985">{{cite doi|10.1016/0162-3095(85)90012-3}}</ref> 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".<ref name=TAC8>Daly & Wilson (1999), p. 8</ref>
   
Since the introduction of the theory of the Cinderella Effect, many psychologists have criticized and collected information, intending to refute the claim that stepparents and abuse in children are directly related. In one such study, John Harrop administered a survey via telephone, asking participants “whether they had ‘slapped’ certain family members (considered one by one) within the last year, had ‘punched’ them, and had ‘used a knife or gun on’ them and so forth, when they had a disagreement or were angry with them’.” (“Truth” 51) For this particular study, although the survey revealed that “the 117 stepparents who did not hang up (…) were no more likely to profess that they had assaulted the children under their care than were genetic parents” (“Truth” 51), the data is biased since those who do assault are unlikely to admit it or participate in such an interview via telephone.
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===Daly and Wilson research===
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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.<ref name=TAC26>Daly & Wilson (1999), p. 26</ref> 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".<ref name="TAC27">Daly & Wilson (1999), p. 27</ref> Their overall findings demonstrate that children residing with stepparents have a higher risk of abuse even when other factors are considered.<ref name="DalyWilson1985" />
   
==Alternative Explanations for Elevated Mistreatment of Stepchildren==
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====Explanation====
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All organisms face [[trade-off]]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|mating effort]], growth, or investment in other offspring).<ref name="Trivers1971">{{cite doi|10.1086/406755}}</ref> 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.
   
There are many skeptics who disregard the Cinderella Effect, convinced that step-relationships are not a direct cause of elevated abuse among children. One alternative explanation is that “a high incidence of abusive stepfamilies could, in principle, be a spurious result of biased detection or reporting.” (“Assessment” 288) Evidence against this shows that when higher criteria is required in the analysis of records, the risk for stepparents to be the perpetrators increases, contrary to skeptics beliefs. Others say that economic backgrounds could be an underlying cause and “one might hypothesize that the stress of poverty cause the poor to be especially likely to abuse and kill their children and also to experience high rates of divorce and remarriage, making steprelationship (''sic'') an incidental correlate of abuse.” (“Cinderella” 5) Although studies show that poverty increases the chances of child abuse, further analysis shows it has little connection to step-relationships. (“Cinderella” 5)
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Daly and Wilson point out that [[infanticide]] is an extreme form of biasing parental investment that is widely [[Infanticide (zoology)|practiced in the animal world]].<ref name="DalyWilson1980">{{cite doi|10.2307/351225}}</ref> For example, when an immigrant male [[lion]] enters a pride, it is not uncommon for him to kill the cubs fathered by other males.<ref name="Bertram1975">{{cite doi|10.1111/j.1469-7998.1975.tb02246.x}}</ref> Since the pride can only provide support for a limited number of cubs to survive to adulthood, the killing of the cubs in [[competition (biology)|competition]] with the new male’s potential offspring increases the chances of his progeny surviving to maturity.<ref name="Bertram1975" /> In addition, the act of infanticide speeds the return to [[Estrous_cycle#Estrus|sexual receptivity]] in the females, allowing for the male to father his own offspring in a timelier manner.<ref name="PackerPusey1983">{{cite doi|10.1086/284097}}</ref> 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.<ref name="DalyWilson1980" />
   
==Sources==
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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.<ref name="DalyWilson1996a">{{cite doi|10.1111/1467-8721.ep10772793}}</ref> 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.<ref name="DalyWilson1996a" />
*Burgess, Robert L., and Alicia A. Drais. "Beyond the "Cinderella Effect": Life History Theory and Child Maltreatment." ''Human Nature'' 10 (1999): 373-395.
 
   
*Daly, Martin, and Margo Wilson. "An Assessment of Some Proposed Exceptions to the Phenomenon of Nepotistic Discrimination Against Stepchildren." ''Annales Zoological Fennici'' 38 (2001): 287-296.
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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".<ref name="Burgess1999">{{cite doi|10.1007/s12110-999-1008-7}}</ref> 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, Martin, and Margo Wilson. "The "Cinderella Effect": Elevated Mistreatment of Stepchildren in Comparison to Those Living with Genetic Parents." ''Trends in Cognitive Sciences'' 9 (2005): 507-508.
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Daly and Wilson report that this parental love can explain why genetic offspring are more immune to lashing out by parents.<ref name="DWHomP.83">Daly & Wilson (1988), p. 83</ref> 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".<ref name="DWHomP.83" /> 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.<ref name="DWBussP.22">Buss (1996), p. 22</ref><ref name="Perkins1979">{{cite pmid|456500}}</ref> 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.<ref name="Perkins1979" />
   
*Daly, Martin, and Margo Wilson. ''TheTruth About Cinderella: a Darwinian View of Parental Love''. London: Orion House, 1998.
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Daly and Wilson’s reports on the overrepresentation of stepparents in [[child murder|child homicide]] and abuse statistics support the evolutionary principle of maximizing one’s inclusive fitness, formalized under [[Kin selection#Hamilton.27s_rule|Hamilton’s Rule]], which helps to explain why humans will preferentially invest in close kin.<ref name="DalyWilson1985" /><ref name="DalyWilson1988a">{{cite pmid|3175672}}</ref><ref name="Hamilton1964">{{cite doi|10.1016/0022-5193(64)90038-4}}</ref> [[Adoption]] statistics also substantiate this principle, in that non-kin adoptions represent a minority of worldwide adoptions.<ref name="DalyWilson1980" /> 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 relationship|coefficient of relatedness]] greater than or equal to 0.125 (e.g., genetic cousins).<ref name="Silk1980">{{cite doi|10.1525/aa.1980.82.4.02a00050}}</ref> 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]].<ref name="Silk1980" />
   
*Daly, Martin, and Margo I. Wilson. "Violence Against Stepchildren." ''Current Directions in Psychological Science'' 1996: 77-81.
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====Methods====
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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.<ref name="DalyWilson1985" />
   
*Gelles, Richard J., and John W. Harrop. "The Risk of Abusive Violence Among Children with Nongenetic Caretakers." ''Family Relations'' Jan. 1991: 78-83.
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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.<ref name="DalyWilson1985" />
   
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Daly and Wilson examined several potentially [[confounding| 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.<ref name="DalyWilson1985" />
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===Attachment theory===
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{{further2|[[Attachment Theory]]}}
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Evolutionary psychologists have also suggested that one of the causes of stepchild abuse may be the lack of a parental [[attachment theory|attachment bond]] 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.<ref name=Cooper1998>{{cite pmid|9599450}}</ref>
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===Misunderstandings===
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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.<ref name=TAC>Daly & Wilson (1999)</ref>
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==Supportive evidence==
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Strong support for the Cinderella effect as described by Daly and Wilson comes from a study of unintentional childhood fatal injuries in [[Australia]].<ref name="Tooley2006">{{cite doi|10.1016/j.evolhumbehav.2005.10.001}}</ref> 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.<ref name="Tooley2006" /><ref name="Wadsworth1983">{{cite doi|10.1136/jech.37.2.100}}</ref> 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.<ref name="Tooley2006" /><ref name="Wadsworth1983" /><ref name="Peterson1997">{{cite pmid|9125098}}</ref> 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.<ref name="Tooley2006" />
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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.<ref name="Tooley2006" /> 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.<ref name="Tooley2006" /> 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.<ref name="Tooley2006" /> 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.<ref name="Tooley2006" /> 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.<ref name="Tooley2006" /> 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.<ref name="Tooley2006" />
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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.<ref name="Anderson1999a">{{cite doi|10.1016/S1090-5138(99)00023-9}}</ref> 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.<ref name="Anderson1999a" /> 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.<ref name="Anderson1999a" /> 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.<ref name="Anderson1999a" /> 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.<ref name="Anderson1999a" /> This studied corroborates the findings of Lynn White, that stepparents in general provide less [[social support]] to stepchildren than their genetic children.<ref name="White1994">White (1994), pp. 109–137</ref>
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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.<ref name="Anderson1999a" /> For example, the authors point out that stepparenting is a [[self-selection bias|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.<ref name="Anderson1999a" /> Anderson and colleagues also conducted a similar study of [[xhosa people|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.<ref name="Anderson1999b">{{cite doi|10.1016/S1090-5138(99)00022-7}}</ref>
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Additionally, a study of [[Hadza people|Hadza]] foragers in [[Tanzania]] by Marlowe also finds evidence of decreased care provided by fathers to stepchildren when compared with genetic children.<ref name="Marlowe1999">{{cite doi|10.1007/s002650050592}}</ref> The author uses the [[Mann-Whitney U| 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.<ref name="Marlowe1999" /> 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.<ref name="Marlowe1999" />
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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.<ref name="Flinn1988">{{cite doi|10.1016/0162-3095(88)90026-X}}</ref> 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.<ref name="Flinn1988" /> 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.<ref name="Flinn1988" /> 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.<ref name="Flinn1988" /> 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.<ref name="Flinn1988" /> 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.<ref name="Flinn1988" />
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==Criticism==
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=== David Buller ===
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[[Philosopher of science]] David Buller, as a part of his general critique of evolutionary psychology <ref name="Holcomb2005">{{cite journal|last=Holcomb|first=H. R.|title=Book Review: Buller does to Evolutionary Psychology what Kitcher did to Sociobiology|journal=Evolutionary Psychology|year=2005|volume=3|pages=392–401|url=http://www.epjournal.net/filestore/ep03392401.pdf}}</ref> has reviewed Daly and Wilson's data. He argues that evolutionary psychology (EP) mistakenly attempts to discover human [[psychological adaptation]]s rather than "the evolutionary causes of psychological traits." Buller also argues that 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 unreasonable to assume that it is motivated by the same kind of psychological mechanism as child homicide. Buller also points out that the conclusion that non-biological parents are more likely to abuse children is contradicted by the fact that even if the rate of abuse among stepparents was disproportionate, most child abuse is in fact committed by biological parents, and that the lowest rate of child abuse is found among adoptive parents.<ref name="Buller2005a">{{cite doi|10.1016/j.tics.2005.04.003}}</ref> 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.<ref name="DalyWilson2005" />
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Buller also argues 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.<ref name="Buller2005b">{{cite doi|10.1016/j.tics.2005.09.008}}</ref> 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.<ref name="Buller2005b" /> 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.<ref name="Crume2002">{{cite pmid|12093940}}</ref> 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.<ref name="Crume2002" /> 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.<ref name="DalyWilson2005">{{cite pmid|16213186}}</ref><ref name="Crume2002" /> 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.<ref name="DalyWilson2005" />
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=== Temrin et al. Sweden study ===
  +
The findings of Daly and Wilson have been called into question by one study of child homicides in [[Sweden]] 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.<ref name="Temrin2000">{{cite doi|10.1098/rspb.2000.1094}}</ref>
  +
  +
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 compared to the North American samples collected by Daly and Wilson, suggesting that there is some degree of cross-cultural variation in the Cinderella effect.<ref name="DalyWilson2001" />
  +
  +
===Alternative hypotheses===
  +
It has been noted by multiple researchers that child abuse is an intricate issue and is affected by other factors.<ref name="Burgess1999" /><ref name="Temrin2000" /><ref name="Giles-Sims1984">{{cite doi|10.2307/584711}}</ref> 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.<ref name="DalyWilson2005" />
  +
  +
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.<ref name="Burgess1999" /> However, they also note that these traits are simply indicative, and do not inevitably lead to child maltreatment.<ref name="Burgess1999" /> 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.<ref name="Temrin2000" />
  +
  +
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.<ref name="Giles-Sims1984" /> 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,<ref name="Tooley2006" /> confessed that "it is certainly difficult to talk about because it is such a hot issue".<ref name=Trounson2008>Andrew Trounson,[http://www.theaustralian.com.au/news/health-science/children-safer-with-biological-parent/story-e6frg8y6-1111116267294 Children 'safer with biological parent'], ''[[The Australian]]'', May 07, 2008</ref>
  +
  +
==See also==
  +
* [[Parenting]]
  +
* [[Parental investment]] theory
  +
* [[Family]]
  +
* [[Paternal bond]]
  +
* [[Maternal bond]]
  +
* [[Nuclear family]]
  +
* [[Cinderella complex]]
  +
* [[The WAVE Trust]]
  +
  +
==Notes==
  +
{{inconsistent citations}}
  +
{{Reflist|30em}}
  +
  +
==References==
  +
*{{cite book|author1=Martin Daly|author2=Margo Wilson|title=Homicide|url=http://books.google.com/books?id=3p4br9FRAUgC|accessdate=4 November 2012|year=1988|publisher=Transaction Publishers|isbn=978-0-202-01178-3}}
  +
  +
*{{cite book|author1=Martin Daly|author2=Margo Wilson|title=The Truth about Cinderella: A Darwinian View of Parental Love|url=http://books.google.com/books?id=L58LY0bShdMC|accessdate=4 November 2012|date=11 October 1999|publisher=Yale University Press|isbn=978-0-300-08029-2}}
  +
  +
*{{cite book|last=Crawford|first=Charles|coauthors=Dennis Krebs|title=Foundations of Evolutionary Psychology|year=2008|publisher=Lawrence Erlbaum Associates|location=New York|isbn=978-0-8058-5957-7}}
  +
  +
*{{cite book|last=Buss|first=David|title=Sex, power, conflict: feminist and evolutionary perspectives|year=1996|publisher=Oxford University Press|location=New York|isbn=978-0-19-510357-1}}
  +
  +
*{{cite book|editor1-last=Booth|editor1-first=A.|editor2-last=Dunn|editor2-first=J.|author=White, Lynn|title=Stepfamilies. Who benefits? Who does not?|year=1994|publisher=Lawrence Erlbaum|location=Hillsdale|isbn=978-0-8058-1544-3}}
  +
  +
== Further reading ==
  +
*{{cite journal
  +
| last = Gelles
  +
| first = Richard J.
  +
| authorlink =
  +
| coauthors = John W. Harrop
  +
| title = The Risk of Abusive Violence Among Children with Nongenetic Caretakers
  +
| journal = Family Relations
  +
| volume = 40
  +
| issue = 1
  +
| pages = 78–83
  +
| publisher = [http://www.ncfr.org/ National Council on Family Relations]
  +
| month = January | year = 1991
  +
| doi = 10.2307/585662
  +
| jstor =585662
  +
}}
  +
* Nigel Barber (June 1, 2009), [http://www.psychologytoday.com/blog/the-human-beast/200906/do-parents-favor-natural-children-over-adopted-ones Do parents favor natural children over adopted ones?], ''The Human Beast'' blog on ''[[Psychology Today]]'', discussing:
  +
* {{cite doi|10.1177/000312240707200105}}
  +
* {{cite doi|10.1016/j.evolhumbehav.2009.01.001}}
  +
* Mindelle Jacobs (July 4, 2010), [http://www.edmontonsun.com/comment/columnists/2010/07/02/14594536.html The Cinderella effect is not just a fairy tale], [[Edmonton Sun]]
  +
  +
{{Parenting}}
  +
{{Cinderella}}
  +
  +
{{DEFAULTSORT:Cinderella Effect}}
 
[[Category:Child abuse]]
 
[[Category:Child abuse]]
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[[Category:Evolutionary psychology]]
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[[Category:Childhood]]
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[[Category:Abuse]]
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[[Category:Family]]
  +
[[Category:Foster care]]
  +
[[Category:Parenting]]
  +
[[Category:Kinship and descent]]
  +
 
{{enWP|Cinderella Effect }}
 
{{enWP|Cinderella Effect }}

Latest revision as of 14:39, September 7, 2013

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In evolutionary psychology, the Cinderella effect is the alleged 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 remnant of an adaptive reproductive strategy among primates where males frequently kill the offspring of other males in order to bring their mothers into estrus, and give the male a chance to fertilize her himself. There is both supporting evidence for this theory and criticisms against it.

BackgroundEdit

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."[1] 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.[2] 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".[3] Studies have found that not biologically related parents are up to a hundred times more likely to kill a child than biological parents.[4]

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.[5] 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.[6] 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."[3]

Evolutionary psychology theoryEdit

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".[7] 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".[8]

Daly and Wilson researchEdit

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.[9] 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".[10] Their overall findings demonstrate that children residing with stepparents have a higher risk of abuse even when other factors are considered.[7]

ExplanationEdit

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).[11] 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.[12] For example, when an immigrant male lion enters a pride, it is not uncommon for him to kill the cubs fathered by other males.[13] 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.[13] 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.[14] 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.[12]

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.[15] 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.[15]

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".[16] 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.[17] 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".[17] 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.[18][19] 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.[19]

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.[7][20][21] Adoption statistics also substantiate this principle, in that non-kin adoptions represent a minority of worldwide adoptions.[12] 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).[22] 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.[22]

MethodsEdit

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.[7]

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.[7]

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.[7]

Attachment theoryEdit

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Evolutionary psychologists have also suggested that one of the causes of stepchild abuse may be the lack of a parental attachment bond 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.[23]

MisunderstandingsEdit

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.[24]

Supportive evidenceEdit

Strong support for the Cinderella effect as described by Daly and Wilson comes from a study of unintentional childhood fatal injuries in Australia.[25] 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.[25][26] 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.[25][26][27] 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.[25]

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.[25] 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.[25] 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.[25] 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.[25] 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.[25] 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.[25]

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.[28] 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.[28] 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.[28] 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.[28] 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.[28] This studied corroborates the findings of Lynn White, that stepparents in general provide less social support to stepchildren than their genetic children.[29]

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.[28] 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.[28] 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.[30]

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.[31] 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.[31] 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.[31]

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.[32] 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.[32] 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.[32] 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.[32] 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.[32] 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.[32]

CriticismEdit

David Buller Edit

Philosopher of science David Buller, as a part of his general critique of evolutionary psychology [33] has reviewed Daly and Wilson's data. He argues that evolutionary psychology (EP) mistakenly attempts to discover human psychological adaptations rather than "the evolutionary causes of psychological traits." Buller also argues that 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 unreasonable to assume that it is motivated by the same kind of psychological mechanism as child homicide. Buller also points out that the conclusion that non-biological parents are more likely to abuse children is contradicted by the fact that even if the rate of abuse among stepparents was disproportionate, most child abuse is in fact committed by biological parents, and that the lowest rate of child abuse is found among adoptive parents.[34] 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.[35]

Buller also argues 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.[36] 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.[36] 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.[37] 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.[37] 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.[35][37] 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.[35]

Temrin et al. Sweden study Edit

The findings of Daly and Wilson have been called into question by one study of child homicides in Sweden 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.[38]

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 compared to the North American samples collected by Daly and Wilson, suggesting that there is some degree of cross-cultural variation in the Cinderella effect.[3]

Alternative hypothesesEdit

It has been noted by multiple researchers that child abuse is an intricate issue and is affected by other factors.[16][38][39] 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.[35]

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.[16] However, they also note that these traits are simply indicative, and do not inevitably lead to child maltreatment.[16] 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.[38]

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.[39] This paper of Giles-Sims and Finkelhor predates however practically all empirical studies on the Cinderella effect.

Ethical issuesEdit

Discussing the implications of this line of research, Australian psychologist Greg Tooley, author of a 2006 study confirming the existence of the effect,[25] confessed that "it is certainly difficult to talk about because it is such a hot issue".[40]

See alsoEdit

NotesEdit

Template:Inconsistent citations

  1. Daly & Wilson (1999), p. 33
  2. Daly & Wilson (2007) Is the "Cinderella Effect" controversial? In Crawford & Krebs (Eds) Foundations of Evolutionary Psychology, pp. 383-400. Mahwah, NJ: Erlbaum.
  3. 3.0 3.1 3.2 Daly, M., M. Wilson (2001). An assessment of some proposed exceptions to the phenomenon of nepotistic discrimination against stepchildren. Annales Zoologici Fennici 38: 287–296.
  4. DOI:10.4236/psych.2011.24062
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  5. Crawford (2008), p. 387
  6. Crawford (2008), p. 388
  7. 7.0 7.1 7.2 7.3 7.4 7.5 DOI:10.1016/0162-3095(85)90012-3
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  8. Daly & Wilson (1999), p. 8
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  40. Andrew Trounson,Children 'safer with biological parent', The Australian, May 07, 2008

ReferencesEdit

  • Crawford, Charles; Dennis Krebs (2008). Foundations of Evolutionary Psychology, New York: Lawrence Erlbaum Associates.
  • Buss, David (1996). Sex, power, conflict: feminist and evolutionary perspectives, New York: Oxford University Press.
  • White, Lynn (1994). Stepfamilies. Who benefits? Who does not?, Hillsdale: Lawrence Erlbaum.

Further reading Edit

Parenting
Brain animated color nevit

Types of parent
Articles concerning parents
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