The Cinderella Effect: Just a Fairytale?

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The Cinderella Effect: Just a Fairytale?

#1  Postby Mr.Samsa » Dec 28, 2010 11:05 pm

The Cinderella Effect is often regarded as one of the great successes of Evo Psych research. It attempts to explain the observation that parents are more likely to kill their stepchildren than their biological children using evolutionary logic - as described by Daly and Wilson: "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". Essentially, the idea is that there are stronger selection pressures for parents to care for their biological children (and their genes) as opposed to non-related children, hence the allusion to Cinderella's treatment by her evil stepmother (and stepsisters).

Unfortunately, some new research seems to suggest that not only is this explanation wrong, but that there might not even be a true observation that needs explaining. Temrin, Nordlund, Rying and Tullberg looked at data in Sweden from 1965-2009 to answer the question of whether this apparent effect is the result of parents being more likely to kill stepchildren, or whether it is simply a result of stepfamilies having higher rates of violence which would skew the data.

Our results show that crime rates are higher among parents in stepfamilies than in families with two genetic parents,
both in the general population and among perpetrators of child homicide in our data set. This indicates that parents in
stepfamilies have characteristics that can increase the risk for child maltreatment, and we regard our results as support
for the hypothesis that the higher incidence of parental child homicide in stepfamilies is an effect of a negative
selection into stepfamilies of individuals who have a higher risk, on average, for committing child homicide. This
explanation for the higher incidence of child homicides in stepfamilies cannot easily be placed in the classical scheme
of ultimate and proximate explanations, but can rather be seen as a confounding or spurious factor that explains the
pattern.


Their results appear to be a perfect falsification of the Cinderella effect: of 27 homicides committed in stepfamilies, 13 stepchildren were killed, 13 biological children, and 1 case of both.

Of course, the research here is still fairly young and needs to be replicated in other areas with different sample populations, but at the very least we have reason to think that the horse and carriage outside the party have just turned back into a mouse and pumpkin.
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Re: The Cindarella Effect: Just a Fairytale?

#2  Postby Thommo » Dec 28, 2010 11:21 pm

:coffee:
jamest wrote:Taken as a whole, I've talked quite a lot of bollocks.
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Re: The Cindarella Effect: Just a Fairytale?

#3  Postby virphen » Dec 28, 2010 11:26 pm

Isn't that just covering homicide though? (just playing devil's advocate)
That wouldn't address whether or not there is such an effect in regard, say, to sexual abuse. (and might there not be the absence of the incest taboo to potentially explain it?)
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Re: The Cindarella Effect: Just a Fairytale?

#4  Postby Mr.Samsa » Dec 28, 2010 11:43 pm

virphen wrote:Isn't that just covering homicide though? (just playing devil's advocate)
That wouldn't address whether or not there is such an effect in regard, say, to sexual abuse.


Indeed, this research was only looking at homicide so it's possible that there would be still be significant differences in other areas like sexual abuse, neglect, etc, but (assuming that the findings in that article are valid) the Cinderella effect would still struggle to explain these findings. It requires us to accept that there is an evolutionary adaptation that causes us to treat our biological children differently from non-biological children, and then it would have to account for the fact that this adaptation does not apply to homicide. It's not impossible for it to be able to adapt to these findings, but it would make it less parsimonious and it's predictive power would suffer a fair bit, I'd imagine.

virphen wrote:(and might there not be the absence of the incest taboo to potentially explain it?)


Indeed, that would be the other issue - if we eliminate homicide from the Cinderella effect, then what we're left with could potentially be explained in better ways. Instead of appealing to a nebulous desire to pass on one's genes, it would clearly be easier to explain any differences in rates of sexual abuse by an incest taboo. Or if we still wanted an evolutionary explanation, we could invoke the Westermarck effect as an explanation for why the parents are less likely to sexually abuse their own children.
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Re: The Cindarella Effect: Just a Fairytale?

#5  Postby Dracena » Dec 29, 2010 2:49 am

:coffee:
Bukhari Volume 8, book 82, hadith 803
Narrated Ash-Sha´bi; from Ali when the
latter stoned a lady to death on a Friday:
Ali said "I have stoned her according to
the tradition of Allah´s Apostle."
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Re: The Cindarella Effect: Just a Fairytale?

#6  Postby Thommo » Dec 29, 2010 10:53 am

Mr.Samsa wrote:
virphen wrote:Isn't that just covering homicide though? (just playing devil's advocate)
That wouldn't address whether or not there is such an effect in regard, say, to sexual abuse.


Indeed, this research was only looking at homicide so it's possible that there would be still be significant differences in other areas like sexual abuse, neglect, etc, but (assuming that the findings in that article are valid) the Cinderella effect would still struggle to explain these findings. It requires us to accept that there is an evolutionary adaptation that causes us to treat our biological children differently from non-biological children, and then it would have to account for the fact that this adaptation does not apply to homicide. It's not impossible for it to be able to adapt to these findings, but it would make it less parsimonious and it's predictive power would suffer a fair bit, I'd imagine.

virphen wrote:(and might there not be the absence of the incest taboo to potentially explain it?)


Indeed, that would be the other issue - if we eliminate homicide from the Cinderella effect, then what we're left with could potentially be explained in better ways. Instead of appealing to a nebulous desire to pass on one's genes, it would clearly be easier to explain any differences in rates of sexual abuse by an incest taboo. Or if we still wanted an evolutionary explanation, we could invoke the Westermarck effect as an explanation for why the parents are less likely to sexually abuse their own children.


Just to dive in with the devil's advocate stuff: The sample size (27 murders, with treated data) is far too small to state with any degree of confidence that no significant difference exists between murder rates for biological children and non biological children, only that no significant difference was found for it. If (and this is the mighty big supposition you were discussing) there was a general pattern of abuse towards non-biological children as compared to towards biological children I don't think it would be reasonable to say that this finding was significantly against the trend - you'd likely need far bigger sample to make it improbable (depending on effect size).
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Re: The Cindarella Effect: Just a Fairytale?

#7  Postby Mr.Samsa » Dec 29, 2010 11:14 am

Thommo wrote:Just to dive in with the devil's advocate stuff: The sample size (27 murders, with treated data) is far too small to state with any degree of confidence that no significant difference exists between murder rates for biological children and non biological children, only that no significant difference was found for it. If (and this is the mighty big supposition you were discussing) there was a general pattern of abuse towards non-biological children as compared to towards biological children I don't think it would be reasonable to say that this finding was significantly against the trend - you'd likely need far bigger sample to make it improbable (depending on effect size).


Unfortunately the sample size is small given that it's a fairly rare event that they're looking at but I suppose there are a few things we need to keep in mind:

1) the numbers are big enough to reach significance in the chi square test
2) the data were taken using information spanning from 1965-2009, which is a huge population to take from (and to sort through), so it will be costly and very time consuming trying to do research on larger populations
3) the research supporting the Cinderella effect uses comparable (and sometimes smaller) sample sizes, and
4) the research supporting the Cinderella effect doesn't take into account the confound of increased violence in stepfamilies (which makes their conclusions very shaky).

So I do agree that before we can make any substantive claims about the "demise of a paradigm" we need to replicate this research, check that it generalises to other populations, etc, but on the other hand, the research supporting the Cinderella effect wasn't exactly concrete so it wouldn't take much to topple it.
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