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Problems of Parenting

Dawkins: Family Planning

Optimal Clutch Size

a. costs of producing too many offspring

1. food spread too thin

2. parenting spread too thin

b. adaptations that limit offspring production:

evolve NOT for benefits of the group, rather

FOR benefit of mother (i.e., genes of the mother)

in maximizing number of surviving children

Conclusions on Family Planning

Genes for having too many children are NOT passed on to next generation, since fewer of the children bearing these genes reach adulthood.

Therefore: Adaptations to produce optimal number of offspring, NOT maximum number of offspring.

Dawkins: Battle of Generations

Parental Investment: Investment

that increases one offspring’s RS

at cost of parent’s ability to invest

elsewhere.

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Should parents invest more

in older child?

a. more costly to get younger one up to

reproductive age

b. but . . . units of PI more beneficial to

younger one

Why do mothers

provide more parental care

than fathers?

The paternity uncertainty

hypothesis

Mothers are 100% “sure” of genetic contribution to offspring

Strongest in species with internal fertilization

Makes parental investment less profitable for fathers than mothers

Mating opportunity cost hypothesis

Higher for males than females

Parental effort versus mating effort– men benefit more from securing

additional mates

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Mating Opportunity Cost

Hypothesis May Explain Individual

Differences Among Men in

Parenting

When surplus of men, men have trouble pursuing ST mating

Men attractive as ST mates predicted to do less parenting.

Population density should lower men’s parenting effort due to more ST mating opportunities

Conclusions about Why Mothers

Invest More than Fathers

Paternity uncertain hypothesis and mating

opportunity cost hypothesis are both

promising.

What are parenting adaptations

sensitive to, theoretically?

Genetic relatedness of

offspring

Ability of offspring to convert

parental care into fitness

Alternative uses of the

resources

Issue #1

Genetic relatedness to child.

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Parents’ investment in children

Different levels of

fathers’ investment in

college education,

depending on:

– Genetic relatedness

– Paternity certainty

– Children of current or

former mate

Two ways of assessing paternity

Partner’s sexual fidelity during the period in which she conceived

Perceptions of the child’s resemblance to him

– Mother’s comments after childbirth

– Relative’s reports of resemblance

Martin Sheen – Apocalypse Now

Charlie Sheen – Platoon

Empirical Evidence

fMRI study: more cortical activation when men look at images of children whose faces resemble their own.

Men whose children look more like them invest more time and attention.

Men who perceive that their wives are loyal and trustworthy invest more in kids.

Sex Differences in Parenting

Women spend more time than men looking at images of infants.

Women are more skilled than men at recognizing emotional expressions of infants

Women are more likely to tend to infants—a cross-cultural universal

Women are more likely to “befriend” others for the goal of helping to protect their infants

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Child abuse and other risks of not

living with both parents

1. Children living with one genetic and one step-parent are roughly 40 times more likely to be physically abused

– "Step-parenthood per se remains the single most powerful risk factor for child abuse that has yet been identified." --Daly & Wilson (1988)

Child abuse risks of not living with

both parents

Child homicide as a function of

genetic relatedness to offspring

Child Murder More Common by

Step Parents

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Thought Experiment

Why do stepparents abuse and kill

stepchildren so much more often than

genetically related children?

Infanticide in Lions

Two Hypotheses About Step-

parental Abuse

1. Byproduct hypothesis: Abuse as byproduct of failure of stepchildren to “engage” the normal psychological mechanisms of parental love (Daly & Wilson).

2. Adaptation hypothesis: Adaptations to inflict costs on, or eliminate, unrelated cost-absorbing kids (Buss & Duntley)

Issue #2

Offspring’s ability to convert parental care

into reproductive success

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Evidence

1. parental neglect and abuse of children

with congenital abnormalities

2. greater maternal care of healthier twin

3. young kids, who are therefore less

reproductively valuable, are killed more

Parental neglect and abuse of children

with congenital abnormalities

12% (16,000) of institutionalized children are never visited

22% (30,000) are visited once a year

As many as 60% of children with congenital abnormalities who live at home are abused

Maternal care based on the health

of the child

Study of maternal behavior

toward twins

– At 4 months, mothers

directed same amount of

positive behavior toward

both twins

– At 8 months, mother

directed more positive

behavior toward healthier

twin with no reversals

Age of child and risk of

infanticide

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Thought Experiment

Why do mothers kill young infants?

Two Competing Hypotheses

Byproduct hypothesis: Because parents feel more love for kids better able to convert parental care into RS, and less love to others, killing is a rare and extreme byproduct of lack of love (Daly & Wilson)

Adaptation hypothesis: Mothers have adaptations to kill infants who are deformed, etc. (Buss & Duntley)

Issue #3

Alternative uses of parental resources.

Age of mother and infanticide

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Women’s marital status and

infanticide

Puzzling Cases of Mothers Who

Kill Children

Parental Effort v. Mating Effort

1. fathers spend less time with kids than mothers, even among the Aka tribe.

2. Women have greater pupillary dilation to pictures of infants [a measure of interest]

Women can read infant facial expressions more accurately and quickly than men.

Conclusions

Young unwed mothers who lack an

investing father are far more likely to kill

infants.

Byproduct or adaptation? -- need

evidence of special design.

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The Trivers-Willard Hypothesis

"In species with a long period of parental investment after birth of young, one might expect biases in parental behavior toward offspring of different sex, according to the parental condition; parents in better condition would be expected to show a bias toward male offspring."

Trivers, R.L., and Willard, D.E., 1973.

Trivers’s Theory of Parent-

Offspring Conflict

Parent-Offspring Conflict

Mother-offspring conflict in utero

Mother and fruit example of diminishing returns

Predictions of parent-offspring conflict

– parents and children will get into conflict about the time the child should be weaned

– parents will encourage children to value their siblings more than they are naturally inclined to do

Mother-Offspring Conflict In Utero

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Oedipal Complex

Freud and his mother

Class Thought Experiment

Would you let you parents choose

your LT mate?

Conflict over mating

Offspring value beauty more than parents:

parents value family background

Conflict over short-term strategies,

particularly for daughters

Conflict over parents choosing a new

mate

Homicide Data

Homicide as assay of conflict: logic of (tip

of iceberg)

No evidence of same-sex contingency

during preschool years

– 21 boys killed by father, 21 boys killed by

mother

– 27 girls killed by father, 27 girls killed by

mother

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Adulthood: evidence of same-sex

contingency

– 60% male-male familial homicides (father or

son victim)

– 27% male killer, female victim

– 5% female killer, male victim

– 9% female killer, female victim

d. In sum: adulthood same-sex contingency

in familial homicides, but this is a decade

after end of Oedipal stage.

Asymmetry of Valuing Parents

and Children

Asymmetry of Valuing Parents

and Children

Genetic r = .50 between parents and children

It does not follow that they value each other

equally

As parents age, they become less and less

valuable to kids

Simultaneously, kids become more valuable to

parents, as other avenues for parent’s fitness

diminish.

Asymmetry of Valuing Parents and

Children, continued…

Prediction: Those less valuable are at more

risk of getting killed

82% of father-son homicides were son killing

father v. 18% father kill son

Perhaps explains why your parents want to see

you more than you see them!

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