Families and Development Flashcards
What are families?
Families are collections of individuals who share many genes by common descent
Why does Evolutionary theory predict a certain amount of conflict within families?
Each individual’s fitness inevitably conflicts to some degree with others in the family
Each individual is related more closely to himself or herself than anyone else
Because family members are not identical, they are bound to disagree to some extent
How is relatedness the basis of conflict within families?
100% to self
50% to immediate family members (assuming no step-parents)
Mother and father
Siblings (on average)
Each family member sees him/herself as more valuable than another
Parents are sources of investment and resources
This can be distributed equally or unequally
Parent-Offspring conflict revolves around the distribution of this investment
Even though parents and offspring are closely related, they are not genetically identical
There will be one distribution that maximizes mom’s genes
There will be a different distribution that maximizes each offspring’s genes
Simple case: Parental Investment
The distribution of investment between two sequential offspring of one mother
For any maternal investment, the mother has a choice
Invest in the current offspring
Ex. Weaning
Prepare her body for another pregnancy
All of the mother’s offspring will carry 50% of her genes
She will favor an equal distribution among offspring
Anytime the benefits of giving investment to a present child do not outweigh the costs of withholding for future offspring, a mother should invest in future offspring
Parent-Offspring Conflict: Offspring View
The offspring’s viewpoint is different from the mother’s
When the mother compares a child to a future child, she sees two equally valuable genetic entities
When the child makes this comparison, he/she reaches a different conclusion
100% related to himself
50% related to his siblings
In terms of spreading his genes, he is twice as good as any sibling he could ever have
Offspring should have been shaped by natural selection to devalue the costs his/her own rearing inflicts on his siblings
Sibling devaluation
Sibling devaluation is not fixed at 0.5, it is variable.
Full siblings are related 50%
Half siblings are related 25%
Half siblings will devalue each other more steeply than full siblings
Parent-offspring conflict will be more intense in mating systems that produce lots of half siblings
Parent-Offspring Conflict / universal
This conflict is universal among mammals
Babies of all species will demand nursing long after mother becomes reluctant
There is no “mutually beneficial” time for weaning to take place
Each party sees the situation differently
The offspring is active in eliciting the investment from the mother
This helps explain the regression to less mature behavior when a new baby appears
This manipulates the mother’s impression of where the offspring might be on the developmental curve
Parent-Offspring Conflict begins before birth
The mother is designed to weigh the value of investing in this particular fetus against the value of potential future fetuses
Negative maternal evaluation
Believed to explain why nearly half of all fetuses are spontaneously aborted
The fetus is more interested in its own survival than the mother
The fetus has evolved hormonal means of manipulating the mother
This provides the fetus with more resources than are in the mother’s best interests
This causes a number of different problems during pregnancy
Maternal diabetes, maternal high blood pressure
Sharing
A parent’s fitness is served by getting as many of her genes as possible into future generations
A parent is equally related to all of her children, so she should invest equally in them
Thus, parents should want their children to share more often than their children would want to
Sibling Rivalry
Children share some genes
Thus, we would expect that children would show concern for the welfare of their siblings.
Children do not share all of their genes. There will inevitably be some conflict
Sibling Rivalry: Twins
Identical twins share 100% of their genes.
One might expect that they are completely unselfish towards each other.
The occurrence of identical twins may have been too rare in human history for this unselfishness to have evolved.
There does exist some evidence that identical twins are less selfish towards each other
Neglect and Infanticide: Mother’s Evaluation
Begins in the womb and continues into childhood. The mother has a motive to evaluate each child as a vehicle for her fitness
A younger child needs more care than an older child
A sick child needs more care than a well child
Should a mother invest in a child that is so sick that it has little chance of making her a grandmother?
Should a mother invest highly in a child during a period of famine, or withhold resource until a better time?
Discriminative parental solicitude
investment in offspring that is conditional on parental resources and offspring’s relatedness, need, health, etc.
Daly and Wilson (1988)
Propose that post-partum blues and post-partum depression are mechanisms to give the mother an objective frame of mind
If the mother were euphoric at birth, she would not be able to ask herself difficult, but adaptive questions
Should I invest in this baby at this time?
In many societies, babies are not named until they are several days old. When it become certain that the are viable
Infanticide is condemned in our society, but has vestigial remains
Women who kill their babies are mostly young, poor, and unmarried
These are the exact conditions in the EEA that would predict low success in raising a child
Scheper-Hughes (1992)
Similar practices occur today, and not just in tribal societies.
Documented parental solicitude in a Brazilian shanytown.
Poverty is so high that 46% of all children die before age 5
Children seen as “little winged angel, fragile bird…”
Conflict Between Father and Mother
The degree of conflict between the father and mother depends on the father’s confidence that his mate’s children are his
Conflict Between Father and Mother: Lions
In some species it is common for the male that has taken a new female to kill all her existing dependent offspring
And sometimes all those born before the required gestation time
The incentive is to get the female to stop investing in another male’s offspring and to become pregnant with his offspring as soon as possible
Step-parent Conflict Over Investment in Children
Provides a clear case of conflict of interest
The stepparent knows for certain that the stepchild is unrelated
Different than in cases of paternal uncertainty because both women and men can become stepparents
Much research exists showing that stepparents disagree with the child’s natural parent over the optimal investment of children
Cinderella has a clear evolutionary basis
Child abuse
The standard explanation of child abuse is that child abusers learned bad parenting skills from their own parents.
This does not explain why stepchildren are at much greater risk than biological children.
Lightcap et al. (1982)
Studied families with 2 parents who each had a biological child and a stepchild.
If bad parenting was the explanation, both children should be equally abused.
Found that adults abused 12 of 21 stepchildren (57%), but 0 of 20 (0%) biological children
Daly and Wilson (1988)
Studied homicides of children.
Extreme cases of abuse.
A child living with one natural and one stepparent is as much as 100 times more likely to be killed than a child living with two natural parents!
This is an extremely strong finding
The results cannot be explained by poverty or other social factors
Perception of Paternity
Evolutionary considerations suggests that
A father should be interested in determining whether the baby is his before investing in its care
A mother should be interested in convincing a potentially investing male that the child is indeed his
Handicapped Children / Lightcap et al. (1982)
Handicapped children are abused more often than non-handicapped children.
Children with physical handicaps would have had a difficult time competing in the EEA.
Handicapped children were less likely to convert maternal investment into grandchildren.
Another example of discriminative parental solicitude that may have been adaptive for our ancestors.
Divorce
Bertzig (1989)
Looked at cross cultural data on divorce from 186 societies
Found that in every region, infidelity and infertility were the most common bases for divorce
These led by a high margin over personality differences, economic problems, problems with in-laws, etc.
These two major causes of divorce involve threats to the reproductive fitness of one or both partners
What is Childhood for?
Why do humans take such a long time to develop?
It isn’t just a matter of growing, many other animals grow to similar adult sizes very rapidly
It has been suggested that childhood allows for time to learn the many skills necessary to function in society
Linguistic skills, social skills, practical skills, etc.
Play
Children’s play changes with age
Infants’ play consists largely of manipulating single objects
Shaking rattles, banging blocks, mouthing dolls, etc.
During the second year, children begin pretend play
Feeding dolls, resting dolls with naps, driving model cars around, etc.
Suggested that play serves the purpose of giving the child practice at skills that would be necessary as an adult
For the infant, this means learning the nature of physical objects. What happens when I bang this?
Older children are learning about social relations
Immaturity
Bjorklund (1997)
Suggests that immaturity may play an adaptive role in a child’s life and development.
Some aspects of childhood are designed by evolution to adapt the child to its current environment, not its future one.
Chicks have temporary structures on their beaks called an “egg tooth” that helps it break out of its shell. It disappears soon afterwards.
Children are oblivious to how poor they are at tasks
A lack of awareness of limitations may prevent them from being discouraged
Allows children to keep attempting to learn necessary life skills
This contributes to a child’s optimism and willingness to compete
This also may be related to children’s failure to detect sarcasm
Reproductive value
the number of future children a person can be expected to produce
Reproductive value is not the same as fertility
A child has zero fertility, but high prospects for producing children in the future.
Reproductive value increases until puberty, when it then begins to decrease with age.
The older you are the fewer children you can expect in the future.
In hunter gatherer societies, reproductive value increases markedly up to about age 15
Grief for LOST Children Depends on Their Age
Maximum grief was reported for children who died at an age corresponding to the peak of reproductive value for hunter-gatherers
This pattern is consistent with conditions in the EEA, not today
The Grandmother Hypothesis
proposes that a time comes when women can further their fitness more by investing in existing kin (i.e. grandchildren) than in trying to produce more of their own children
Menopause may have evolved to switch women from investing in producing children of their own to investing in kin
This hypothesis still needs further evidence
Life History Theory (LHT)
A framework that addresses how (in the face of trade-offs) organisms should allocate time and energy to tasks and traits in ways that maximize their fitness
Optimal allocations vary across the life course
LHT concerns the evolutionary forces shaping the timing of life events involved in
Development
Growth
Reproduction
Aging- SENSES-
