Thread by @RTerriers2

Cinderella effect

In evolutionary psychology, the Cinderella effect is the phenomenon of higher incidence of different forms of child abuse and mistreatment by stepparents than by biological parents. It takes its name from the fairy tale character Cinderella,

which is about a girl who is mistreated by her stepsisters and stepmother. Evolutionary psychologists describe the effect as a byproduct of a bias towards kin, and a conflict between reproductive partners of investing in young that are unrelated to one partner.

There is both supporting evidence for this theory and criticism against it.

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 and homicide comes from a variety of sources

including official reports of child abuse, clinical data, victim reports, and official homicide data. Studies have concluded that "stepchildren in Canada, Great Britain, and the United States indeed incur greatly elevated risk of child maltreatment of various sorts, especially

lethal beatings".

Powerful evidence in support of the Cinderella effect comes from the finding that when abusive parents have both step and genetic children, they generally spare their genetic children. In such families, stepchildren were exclusively targeted 9 out of 10 times

in one study and in 19 of 22 in another. In addition to displaying higher rates of negative behaviors (e.g., abuse) toward stepchildren, stepparents display fewer positive behaviors toward stepchildren than do the genetic parents. For example, on average, stepparents invest less

in education, play with stepchildren less, take stepchildren to the doctor less, etc. This discrimination against stepchildren is unusual compared with abuse statistics involving the overall population given "the following additional facts: (1) when child abuse is detected,

it is often found that all the children in the home have been victimized; and (2) stepchildren are almost always the eldest children in the home, whereas the general ... tendency in families of uniform parentage is for the youngest to be most frequent victims."

Evolutionary psychology theory

Evolutionary psychologists Martin Daly and Margo Wilson propose that the Cinderella effect is a direct consequence of the modern evolutionary theory of inclusive fitness, especially parental investment theory. They argue that human child rearing

is so prolonged and costly that "a parental psychology shaped by natural selection is unlikely to be indiscriminate". According to them, "research concerning animal social behaviour provide a rationale for expecting parents to be discriminative in their care and affection,

and more specifically, to discriminate in favour of their own young". Inclusive fitness theory proposes a selective criterion for the evolution of social traits, where social behavior that is costly to an individual organism can nevertheless emerge when there is a statistical

likelihood that significant benefits of that social behavior accrue to (the survival and reproduction of) other organisms whom also carry the social trait (most straightforwardly, accrue to close genetic relatives). Under such conditions, a net overall increase in reproduction of

the social trait in future generations can result.

The initial presentation of inclusive fitness theory (in the mid 1960s) focused on making the mathematical case for the possibility of social evolution, but also speculated about possible mechanisms whereby a social trait could

effectively achieve this necessary statistical correlation between its likely bearers. Two possibilities were considered: One that a social trait might reliably operate straightforwardly via social context in species where genetic relatives are usually concentrated in a local

home area where they were born ('viscous populations'); The other, that genetic detection mechanisms ('supergenes') might emerge that go beyond statistical correlations, and reliably detect actual genetic relatedness between the social actors using direct 'kin recognition'.

The relative place of these two broad types of social mechanisms has been debated (see Kin selection
en.m.wikipedia.org/wiki/Kin_selec…
 and Kin recognition en.m.wikipedia.org/wiki/Kin_recog…), but many biologists consider 'kin recognition' to be an important possible mechanism.

Martin Daly and Margo Wilson follow this second mechanism, and expect that parents "discriminate in favour of their own young", i.e. their actual genetic relatives.

Daly and Wilson research

The most abundant data on stepchild mistreatment has been collected and interpreted by

psychologists Martin Daly and Margo Wilson, who study with an emphasis in Neuroscience and Behavior at McMaster University. Their first measure of the validity of the Cinderella effect was based on data from the American Humane Association (AHA), an archive of child abuse reports

in the United States holding over twenty thousand reports. These records led Wilson and Daly to conclude that "a child under three years of age who lived with one genetic parent and one stepparent in the United States in 1976 was about seven times more likely to become a

validated child-abuse case in the records than one who dwelt with two genetic parents". Their overall findings demonstrate that children residing with stepparents have a higher risk of abuse even when other factors are considered.

Explanation

All organisms face trade-offs as to

how to invest their time, energy, risk, and other resources, so investment in one domain (e.g., parental investment) generally takes away from their ability to invest in other domains (e.g. mating effort, growth, or investment in other offspring).

Investment in non-genetic children therefore reduces an individual's ability to invest in itself or its genetic children, without directly bringing reproductive benefits. Thus, from an evolutionary biology perspective, one would not expect organisms to regularly and deliberately

care for unrelated offspring.

Daly and Wilson point out that infanticide is an extreme form of biasing parental investment that is widely practiced in the animal world. For example, when an immigrant male lion enters a pride, it is not uncommon for him to kill the cubs fathered

by other males. Since the pride can only provide support for a limited number of cubs to survive to adulthood, the killing of the cubs in competition with the new male's potential offspring increases the chances of his progeny surviving to maturity.

In addition, the act of infanticide speeds the return to sexual receptivity in the females, allowing for the male to father his own offspring in a timelier manner. These observations indicate that in the animal world, males employ certain measures in order to ensure that parental

investment is geared specifically toward their own offspring.

Unlike the lion, however, humans in a stepparenting situation face a more complicated tradeoff since they cannot completely disown their partner's offspring from a previous relationship, as they would risk losing

sexual access to their partner and any chance of producing potential offspring. Thus, according to Daly and Wilson, stepparental investment can be viewed as mating effort to ensure the possibility of future reproduction with the parent of their stepchild.

This mating effort hypothesis suggests that humans will tend to invest more in their genetic offspring and invest just enough in their stepchildren. It is from this theoretical framework that Daly and Wilson argue that instances of child abuse towards non-biological offspring

should be more frequent than towards biological offspring.

One would therefore expect greater parental responsiveness towards one's own offspring than towards unrelated children, and this will result in more positive outcomes and fewer negative outcomes towards one's own

children than towards other children in which one is expected to invest (i.e., stepchildren). "If child abuse is a behavioral response influenced by natural selection, then it is more likely to occur when there are reduced inclusive fitness payoffs owing to uncertain or low

relatedness". Owing to these adaptations from natural selection, child abuse is more likely to be committed by stepparents than genetic parents—both are expected to invest heavily in the children, but genetic parents will have greater child-specific parental love that promotes

positive caretaking and inhibits maltreatment.

Daly and Wilson report that this parental love can explain why genetic offspring are more immune to lashing out by parents. They assert that, "Child-specific parental love is the emotional mechanism that permits people to

tolerate—even to rejoice in—those long years of expensive, unreciprocated parental investment". They point to a study comparing natural father and stepfather families as support for the notion that stepparents do not view their stepchildren the same as their biological children,

and likewise, children do not view their stepparents the same as their biological parents. This study, based on a series of questionnaires which were then subjected to statistical analyses, reports that children are less likely to go to their stepfathers for guidance and that

stepfathers rate their stepchildren less positively than do natural fathers.

Daly and Wilson's reports on the overrepresentation of stepparents in child homicide and abuse statistics support the evolutionary principle of maximizing one's inclusive fitness, formalized under

Hamilton's Rule, which helps to explain why humans will preferentially invest in close kin. Adoption statistics also substantiate this principle, in that non-kin adoptions represent a minority of worldwide adoptions. Research into the high adoption rates of Oceania shows that

childlessness is the most common reason for adopting, and that in the eleven populations for which data was available, a large majority of adoptions involved a relative with a coefficient of relatedness greater than or equal to 0.125 (e.g., genetic cousins).

It is also observed that parents with both biological and adopted children bias the partitioning of their estates in favor of the biological children, demonstrating again that parental behavior corresponds to the principles of kin selection.

If you're interested in continuing to read about this, click here; en.wikipedia.org/wiki/Cinderell… and scroll to "Methods".

I've read more than enough. My Step-father is a perfect example of this.

@threadreaderapp unroll please