FAMILY VIOLENCE
A DARWINIAN
PERSPECTIVE
By: Nicole Kessler
Fairy Tales


The narrative histories of western cultures
have been rife with evil step-parent tales
(Hansel and Gretel, Sleeping Beauty,
Snow White, & Cinderella).
Are these stories completely fiction or are
they representative of a real
phenomenon?
Class Predictions


Are step children treated the same as biological
children?
Given what we know now about evolutionary
psychology what would you predict?
Concepts to Consider

Inclusive Fitness: Is an organism's direct fitness
(how many of its own offspring it produces and
supports) plus it’s indirect fitness (the fitness
individuals derived from increasing the survival of
their relatives' offspring, whom share some
percentage of their genes).
Concepts to Consider

Parental Investment: Any expenditure that benefits
the offspring at the cost of the parents well being,
other offspring, or future parental reproductive
abilities.
Compelling Examples from the Animal
World


Male yellow-headed
blackbirds will adopt the
offspring of another male,
only when this allows the new
male access to the female.
It is considered a mating
display for the male to show
what a great parent he would
be.
Compelling Examples from the Animal
world


But male barn
swallows kill the
offspring of other
male swallows.
This scenario is
significantly more
common in the
animal kingdom.
Compelling Examples from the Animal
World



When a male lion acquires a
new pride, he will often kill
offspring that are not his own.
Cubs are in the most danger
This is advantageous to the
male lion for two reasons
1. Resources will not be
diverted to raising a nonrelated cub.
2. Female lions will enter
estrus more quickly, allowing
the new male lion to
impregnate her.
Humans



Except in rare cases, such an overt and brutal
practice would not be accepted.
Murdering your new spouses children will generally
limit your access to your new spouse and hence your
ability to produce more offspring.
Are humans so rationally and humanely evolved
that this effect has disappeared?
Daly & Wilson



In the 1970’s two Canadian Psychologists, Martin
Daly and Margo Wilson, began researching the
question of variations in parental solicitude.
Daly & Wilson predicted that step-parents would
feel less inclined to care for their step-children than
natural parents.
Lack of care towards a child increases the
likelihood of abuse. Abuse is what Daly & Wilson
measured.
Disclaimer



We are not talking about every step-parent, stepchild relationship.
Most step-parents are not abusive.
Daly & Wilson are looking at the extreme
malfunction of the step-parent step-child
relationship to see if there is a pattern of stepparents having less parental solicitude.
Daly & Wilson
7
6
5
4
Two Natural Parents
3
One Natural and one
step-parent
2
1
0
Age 0-2 Age 3-5 Age 6-9 Age 10- Age 1413
17

Child abuse cases validated by American Humane Association in 1976
expressed as rated per thousand like-aged children in the reporting
areas.
Daly & Wilson

Daly and Wilson also looked at
child abuse in homes in Hamilton
Ontario in the early 1980’s.
Daly & Wilson
14
12
10
8
Two Natural Parents
6
One natural and one step
parent
4
2
0
Age 0-4
Age 5-10
Age 11-16
Child Abuse Cases handled by the children’s aid societies of Hamilton-Wentworth
expressed as rates per thousand like-aged children in the region.
Daly & Wilson Conclusions


As you can see the Canadian child abuse data
showed a very similar distribution to the American
child abuse data.
Results showed that children in homes with one
step-parent and one biological parent were 40
times more likely to be abused than children in
homes with two biological parents.
Possible Confounds?



People who get divorced (and hence
remarried) are just more violent.
Poverty
Reporting Bias
People who divorce are more violent
overall.



This argument does not stand up in the
face of selective abuse.
In the Hamilton study there were 10
homes that had both step-children and
children from the current marriage. In 9
out of the 10 ONLY the step child was
abused.
Lightcap, Kurland and Burgess (1982)
gathered observational data on known
abusive families in rural Pennsylvania,
and consistently found ONLY stepchildren being abused.
Poverty

Daly and Wilson found that the SES status of
two biological parent households showed a
similar distribution to households with one step
and one biological parent. Poverty is not a
confound.
Reporting Bias


Reporting Bias—It’s possible that step-parents don’t
actually abuse more often just that it is reported
more often. This is a difficult confound to overcome
when doing archival research.
Daly and Wilson argue that reporting bias is almost
eliminated in homicide cases.
Homicide Data



In an analysis of data
from1974-1983 there were
43 Canadian 1 year old killed
by ‘parents’.
11 of the 43 (25.6%) were
killed by step-parents.
If step and natural parents
killed at the same rate the
expected rate would be under
1%. (Daly & Wilson ’85)
Homicide Data


Daly & Wilson analyzed all homicides of pre-school
aged children in Detroit in 1972.
Their analysis revealed that 4 of the 7 murders
were committed by step-fathers that’s 57%. (Daly &
Wilson ’82)
Homicide Data



Scott reviewed data on British ‘fathers’ who killed
their children (under 5 years old)
He found that 15 out of 29 British ‘fathers’ who
killed their children were in fact step-fathers, again
52%. (Scott ‘73)
Over representation of step-parents in infanticide
cases.
Why young children?



They are more vulnerable and less
able to defend themselves.
From the step-parents point of view
infants will demand the most
resources (as compared to say
adolescents).
The bond with children grows as
they get older (remember Selena’s
presentation), maybe the natural
parent is more likely to protect
older children.
Summary


It’s been shown that children living in homes with
both step and natural parents are at a higher rick
for abuse and homicide than children living with two
natural parents.
Younger children are at an even higher risk for both
abuse and homicide.
Summary






Taking into consideration…
Inclusive Fitness & Kin Selection,
Parental Investment Theory
Animal Models
And the data presented today
It follows from a Darwinian framework that…
Summary




Parental solicitude varies as a factor of relatedness
to the child.
People don’t like others children as much as they
like their own so…
People are not willing to make as many sacrifices
for others children
and in extreme cases will harm or kill those children.
Conclusion

Fairy Tales are true!
Sources Cited







Daly, M, and Wilson, M. "The Darwinian Psychology of Discriminative Parental Solicitude."
Nebraska Symposium on Motivation 35(1988):91-144.
Daly, M, and Wilson, M. "Violence against stepchildren." Current directions in psychological
science 5.3 (1996):77-81.
Daly, M, and Wilson, M. “Discriminative Parental Solicitude - A Biological Perspective." Journal
of Marriage and Family 42.2 (1980):277-288.
Daly, M, and Wilson,M.. "Some Differential Attributes of Lethal Assaults on Small Children by
Stepfathers versus Genetic Fathers." Ethology and sociobiology 15.4 (1994):207-217.
Daly, M, and Wilson, M. "An assessment of some proposed exceptions to the phenomenon of
nepotistic discrimination against stepchildren." Annales zoologici Fennici 38.3-4 (2001):287296.
Hamilton, L., Cheng, S, and Powell, B. "Adoptive parents, adaptive parents: Evaluating the
importance of biological ties for parental investment." American sociological review 72.1
(2007):95-116.
Lightcap, J.L., Kurland, J.A., and Burgess, R.L. Child Abuse: A test of some predictions from
evolutionary theory. Ethology and Sociobiology, 1982, 3:61-67
Sources Cited




Daly, M, and Wilson,M.. "Some Differential Attributes of Lethal
Assaults on Small Children by Stepfathers versus Genetic Fathers."
Ethology and sociobiology 15.4 (1994):207-217.
Daly, M, and Wilson, M. "An assessment of some proposed
exceptions to the phenomenon of nepotistic discrimination against
stepchildren." Annales zoologici Fennici 38.3-4 (2001):287-296.
Hamilton, L., Cheng, S, and Powell, B. "Adoptive parents, adaptive
parents: Evaluating the importance of biological ties for parental
investment." American sociological review 72.1 (2007):95-116.
Lightcap, J.L., Kurland, J.A., and Burgess, R.L. Child Abuse: A test of
some predictions from evolutionary theory. Ethology and
Sociobiology, 1982, 3:61-67
Questions, Comments, Concerns?
…FIN