Trivers stated “ that resource allocation that
would maximise parental fitness are not
always the same as those which maximise
Kin Selection Theory (Hamilton 1964) states that we
tend to behave more altruistically towards people we
are related to.
So why are so many families experiencing conflict?
We only have to look at the Jeremy Kyle show to see
that families are very often in conflict with each other.
Children desire greater investment than their parents
are willing to provide.
Parents try to allocate resources to their offspring in
order to ensure that the maximum number of
However, conflict occurs when each child wants more
resources than the parent is prepared to give.
As we have discussed last lesson, parents invest significant
amount amounts of time to their offspring to ensure their
survival. We noted that mothers’ investments were more
emotional and nurturing, whereas the fathers’ investment
tended to be more financial and protecting.
Part of the mother’s ‘nurturing’ job is to ensure the baby is
adequately fed. Mothers today tend to breast feed from
birth to around a year old. The child is then ‘weaned’
around 6 months old, although this is different among
So where does the weaning conflict come in?
Benefits of breast feeding
Mother- child bond is formed and strengthened.
If a mother is breast feeding one child it delays the
birth of any more children.
Preventing the mother from having more children is a
big benefit to the child as they will have all their
parent’s investment and resources.
Badcock (2000)- found that the birth of a subsequent
child within the first four to five years of a child’s life is
the biggest threat to that child’s continued existence!
Freud on breast feeding!
Freud’s psychoanalysis theory places great importance
on the oral stage of development.
It is very difficult for a mother to maintain and nourish
two babies that are born close together.
Constant sucking of a mothers’ nipples by the baby
inhibits the re-establishment of the mothers
menstrual cycle therefore preventing another baby
being born (another child to share their valuable
resources with which could be detrimental to their
survival in some countries and in our past).
Evolution on breast feeding!
Survival of the fittest!
If babies learn to suck their mother’s nipples
constantly and thus prevent the mother from
producing any subsequent children the baby is more
likely to save as they won’t have to compete for their
life source (their food).
Therefore the babies that are the best ‘suckers’ will
survive and pass this survival trait onto the next
Trivers (1974) argues two problems exist
Parents and children will be in conflict about when a
child should be weaned, with the child wanting to get
the resources for longer, while the parents will want
to have more children to ensure the maximum
survival of their genes.
Parents encourage children to value siblings more
than they are naturally inclined to.
Competition between siblings
According to Buss (1999)
The child will want to delay
weaning as long as
possible, often in contrast to
Parents encourage their
children to value their
siblings more than they
Parents punish conflict
between siblings and reward
co-operation, against the
child’s natural instincts.
A parent shares 50% of her genes with each child
and is inclined to spread resources equally among
all children in the family.
However a child shares 50% of genes with a sibling
but 100% with him/herself so may not always be
inclined to share.
Conflict exists before and after
During pregnancy – the potentially fatal condition
At some point when a new child is born the parent has to
transfer investment from the older child to more
Sibling rivalry also exists in the animal kingdom. For
example the black eagle- An extreme type of sibling rivalry
occurs when young animals kill their siblings. For
example, a black eagle mother lays two eggs, and the firsthatched chick pecks the younger one to death within the
first few days.
In humans sibling rivalry is usually more intense when
the children are closer in age and of the same gender
What is your position in the family?
If you are the oldest what are your first memories of a
sibling being born?
How do your parents view your personalities, how would
they describe the differences between you?
How often do you fight or argue?
Do you believe birth order influences your personality?
Do parents have favourites?
How much do you know about middle child syndrome?
Freud saw sibling rivalry as an extension of the
Oedipus complex with brothers competing for the
mother’s attention or little girls competing for their
father’s attention. In the case of little Hans his phobia
was linked to the jealousy of the birth of his young
Alder – saw siblings as striving for significance and
felt birth order was an important aspect of
Some famous siblings
Noel and Liam Gallagher
Kylie and Dannie Minogue
David and Ed Miliband
What do the Psychologists say?
Search David and Ed Miliband brothers in arms
or brothers at war? - Telegraph
Evolutionary theory predicts that women would want to
become grandmothers, the problem with this concept is
that grandchildren are only 25% of their genes unlike their
own children who are 50%.
Therefore it is more beneficial for a woman to have her own
children rather than grandchildren.
According to this concept mothers and daughters will be in
a state of conflict with their young daughters for the right
to reproduce. If the mother has to invest in the upbringing
of the grandchild their resources are being withdrawn from
the children that are 50% their genetic make-up.
Mother-daughter conflict continued…
Workman and Reader (2008) suggest that a
‘reproduction suppression mechanism’ may exist and
is responsible for controlling the likelihood of a
daughter becoming pregnant while their mother is still
of a reproductive age.
It is thought that as daughters will share the same
percentage of genetic make-up with subsequent
siblings or children of their own. So they don’t feel the
need to reproduce while they are still young and
inexperienced and would struggle to provide enough
investment into the child for them to survive.
Evaluation of the parent-offspring
Lack of evidence among human groups
Small sample sizes of human participants therefore
not particularly generalisable.
Read the studies used to evalute the P-O conflict on
page 119-120 and make your own notes.
Describe and evaluate evolutionary explanations of
parental investment (for example, sex
differences, parent-offspring conflict) 24 marks
Swap your essay and using the AO1/AO2 sheet tick all
the points you have mentioned and put an AO1/2 on
Accurate and welldetailed.
Generally accurate and Range
Rudimentary and may
be muddled and/or
Very brief or
The AO1 mark I would give is ______________
Not effective May be
No creditworthy material
Type up your notes and add other studies to enhance
Re-write your essay to improve the grade.
Due in Wednesday 20th November