Is the 'Cinderella effect' real or a damaging myth?
Evolutionists trying to understand why stepdads kill at a disproportionate rate say the 'evil' step-parent is no fairytale - but a killer instinct borne of resentment at nurturing someone else's genepool. Others say it's not so simple. Talia Shadwell reports as part of Stuff's Faces of Innocents series.
James Whakaruru, Coral-Ellen Burrows, Saliel Aplin and Olympia Jetson's names are marks on a long and sorry rollcall of children brutally slain by their stepfathers.
A provocative theory applied to New Zealand's figures for the first time to explain why a violent few fatally batter their partners' small children - yet spare their own- suggests it's not just that they are mad, bad or sad.
The so-called "Cinderella effect" says humans are not biologically programmed to raise other people's offspring.
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However, a family living expert says the theory fuels a damaging stereotype that men who step up to raise another bloke's child are killers in waiting.
Although fewer stepdads kill children than biological fathers, it is frequently reported they kill at a vastly higher rate around the world - because fewer small children live with stepfathers than with their birth parents.
Studies in Australia showed fatal batterings of small children were 300 times more likely to occur at the hands of a stepfather than a genetic parent.
British children were also 100 times more likely to be murdered by their stepfather.
Figures assembled by Stuff for the Faces of Innocents project, show 33 men have been convicted of killing their partner's children since 1992, compared to 56 mothers and 50 fathers.
THE 'CINDERELLA EFFECT'
Why stepfathers kill their lovers' small children but spare their own has troubled Canadian evolutionary psychologist Martin Daly for decades.
He and his late wife Margo Wilson founded the Cinderella theory in the 1980s, researching the deaths of 700 Canadian children.
What they found suggested the unconditional love a parent feels for a screaming child who has soiled their nappy, is not innate for a stepparent - and makes them more likely to lash out.
Evolutionary psychologist Dr Martin Daly, professor at Canada's McMaster University, who discovered the "Cinderella Effect."
The Cinderella theory excluded adoptive or foster parents, as they had invited the child into their homes, unlike step-parents who found their new wards part of the romance package.
Building on Darwin's theory of evolution, the relationship between the new man on the scene and his lover's child is forged by biological altruism, Daly and Wilson found.
That means humans, like other animals, are programmed to investing their time into reproducing their own genes - not someone else's - and sometimes that resentment becomes deadly.
But as the children grew older, and the step parents invested more time in the bond, fewer killed, Daly and Wilson found.
"We've got a phenomenon - and it's the same with animals, such as with birds - where a mother is abandoned and someone steps in, in a parenting role," he explained, from McMaster University in Canada.
"My argument, in psychology - and it's the same with those other animals who engage in step-parenting - is the step-parent is doing it as a courting step.
"People love their own children more than they love someone else's child. That's not to say they don't love them... [but] generally, they're not going to throw themselves in front of a truck for them."
In the Canadian research, birth parents overwhelmingly smothered or shot their children, and a third of fathers committed murder-suicide.
Stepfathers usually beat children to death and just 1 in 67 killed themselves too, Daly and Wilson found.
NOT ALL ABOUT DAD
To determine whether having a "stepdad" - or a mother with a new boyfriend - was a risk factor for Kiwi kids, researchers would need to know how many lived in blended families versus with birth parents, and for how long, Daly said.
A 2009 Government survey found one in five Kiwi children had lived in a stepfamily household before they turned 17, but crime statistics about blended families are limited.
A cursory analysis of New Zealand's murder rates suggested a "Cinderella effect" possibly explained why almost as many stepdads as biological fathers killed here, Daly said.
"I think there is no question that there is a huge over-representation that would be statistically significant if you had that information."
Critics of the "Cinderella Effect" claimed Daly and Wilson minimised dysfunctional household factors like poverty, drug, and alcohol abuse.
Those were additional risk factors for child homicide - but none explained why an abusive step-parent almost always spared their own children, Daly said.
His Canadian study found when an abusive man's kids lived in the household too, in 9 out of 10 cases only the stepchildren were abused.
The poverty theory was troubling as the public used it to judge solo mothers who invited violent boyfriends into their homes, Daly said.
"If the middle classes won't say 'there but for the grace of God go I' - they say, 'Oh, these lower class people are a sorry lot.' They can say that. But there's nothing to say that's why there was an increased risk of abuse from the step-parent."
Daly cautioned against interpreting the research to support views that marriage should be sacrosanct.
"We have not got research for what the outcome is for kids if their parents stay together when they are unhappy. I think there's a fairly strong case that it's not likely to be safe for the kids or the parents for them to stay together."
Benny Haerewa, who beat his stepson James Whakaruru to death in 1999 has since been released from jail.
MAKING A CONNNECTION
Victoria University family psychology adjunct professor Jan Pryor, who has written a book about stepfamily life, said the concept of a "Cinderella Effect" undermined stepdads' usually successful efforts to love and care for their wards.
The average age for a New Zealand child to be killed by their stepfather is three years old.
For that reason, Pryor said many of the men who killed a lover's small child should not be defined as "stepfathers."
She echoed Daly and Wilson's finding that the risk of murder lessened as a stepchild aged - surmising the men who killed in fits of rage were probably new boyfriends with little attachment to the baby.
"In a sense it is more appropriate to say 'the man the mother was sleeping with,' or 'the man the mother was in a relationship with'," Pryor said.
She pointed out that if the drive to nurture a child was biological, men raising a child they were unaware was not actually theirs should feel an innate resentment towards them they themselves could not explain.
The theory also did not explain whether solo-mothers living financially strained lifestyles were targeted by men who preyed upon them and their children, Pryor said.
Most stepfamilies functioned successfully - and the key was to try slowly to build a relationship with them, Pryor said.
"They work hard to make it work because step-parenting is a big ask. But just because they are not theirs doesn't mean they are going to kill the kids. So many stepfathers do the best they can for those kids."
Daly said it was wrong to label every stepdad a potential killer.
"Most stepparent families do function pretty well."
"I think everybody is capable of evil intent. If you look deep inside your black soul even you are capable of evil intent today. Whether you're going to actually going to carry it out is a whole other question."