Lecture 7 (Parental Investment & Parent-Offspring Conflict) - Slides

Question 1

Parental Investment
(Why do mothers provide more care than do fathers? 2 Hypothesis)

Answer 1

• Females give more care because the sexes have different goals.
• These hypothesis are not mutually exclusive.
  1) Paternity Uncertainty Hypothesis
• Females are sure of maternity but there is always a chance of cuckoldry for males (due to internal fertilization)
• Therefore, less advantageous for males to invest compared to moms

2) Mating Opportunity Hypothesis
- Parental effort reduces available mating effort for both men/women
- Mating opportunity is more important for males and missing chances is more costly
- Paternal care should track availability of mates

Question 2

Benefits of Paternal Investment

Answer 2

• 45% mortality if father leaves before 15th birthday, 20% if stays in hunter-gatherers
• Correlated with academic, social skills and later SES

Question 3

Factors Influence Parental Care

Answer 3

1 ) Genetic relatedness to offspring

• Selection favours discriminative parental investment, phenotypic resemblance should therefore influence investment more in fathers than mothers
• Platek, Alvergne, Daly & Wilson, Step-parenting evidence, Anderson

2) Ability to convert parental care into fitness
- Homicide, high/low risk infants, Tribers-Willard Hypotehsis, status

3) Alternative uses of the resources available to invest
- Effort allocated to one activity must take away from others (i.e. future reproduction)
- Wilson/Daly(infanticide and moms age and marital status), Marlowe

Question 4

Platek et al. 2002

Answer 4

1) Genetic Relatedness to Offspring
- Morphed photos of men with an unrelated child
- Presented participant with 3 photos (1 being the self-morph)
- Asked who would you adopt/punish/other questions
- Males across almost all questions have a preference for the self-morph
- Phenotypic resemblance effects males more than females

Question 5

Alvergne et al. 2009

Answer 5

1) Genetic Relatedness to Offspring
- Hunter-Gatherer polygynous subsitence farmers in senegal
- Gathered parental investment info through interviews and child physical condition (BMI, Biceps), took pictures of family and children
- Asked people to look at 3 adults and decide which of the 3 is the childs father (also did t-shirt smell test)
- Facial resemblance was detectable, odour was not.
- Father child resemblance predicted paternal investment and investment predicted health/size
- Facial cues and odour may be a backup cue of relatedness.

Question 6

Step-Parenting

Feelings, resources, cinderella

Answer 6

1) Genetic Relatedness to Offspring
- Step parents spend less $ on tuitino for steps
- Step-moms spend less $ per child, and less likely to have dental/doctor visits
- Preferential reproduction of relatedness
- 57% of step-dads and 25% of step-moms report parental feelings for step kids
- Step-kid/parent interactions are less frequent and more aggressive
- Cinderella effect: step-moms are more emotional distance and punitive to step-kids.
- Hunter-gatherers (see slide)

Question 7

Step-Parenting (hunter-gatherer)

Answer 7

• Step-dads: spend less time with steps, dont play with them, help less with homework, and some are required to be killed as a condition of marriage.

Question 8

Anderson et al 1999

Answer 8

• The likelihood of going to university depends on whether dad co-resides with mom and whether he is a step dad
• Step kid living with dad and related kids not living with dad go to uni at equal rates
• Related kid living with dad is highest and step kid without is the worst

Question 9

Wilson/Daly (Step-parenting & homicide)

Answer 9

• Families with step kids only or with some step kids go to shelters much more
• Uxorcides are substantially higher if mom has only step kids in care, second to mixed family
• Also, step-parents kill step-kids at alarmingly higher rates, especially between years 0-5 compared to genetically related families
• Murders of children by fathers almost double for step dads than for genetic dads. Suicides at the scene for genetic dads is inordinately higher though and implies mental health issues or guilt of actions

Question 10

Ability to convert care into fitness (homicides, high/low risk infants)

Answer 10

• Homicides for non-relatives go up only at 17 (when they become reproductive)
• Homicides by relatives is highest at youngest age (cuckoldry and best time to do it since you haven’t invested much care)
• Children with congenital abnormalities are more abused and neglected (60% vs. 1.5), Healthy infants receive more positive maternal attention
• 0% parental investment = much less likely to survive
• When fewer resources, high risk infants receive less, but with many resources they will receive more (Once you satisfy basic investment needs you will invest more in high risk to better allocate and maximize fitness)

Question 11

Trivers-Willard Hypothesis

and evidence

Answer 11

• Parents will produce/invest in sons when parental/environment conditions is good. Daughters when poor
• Poor conditions more costly to males than females (due to variance in reproductive success)
• Among higher classes, girls more likely to be killed.
• Hunter-gatherers: poorer families invest more in daughter’s education
• Sons of high status men attained more years of education than did daughters
• High status men desire sons over daughters

Question 12

Wilson & Daly (Evidence for 3)

Also married vs. unmarried

Answer 12

• Moms commiting infanticide with their own children MUCH higher when mom is very young.
• When women are young, they have a greater reproductive POTENTIAL, and having a child may be more costly to their future potential as a result
• Might be better to invest in future opportunities at that age
• Infanticide rises again around 35, may be due to congenital effects or slim-pickings
• Unmarried young women commit infanticide way higher than married
• Married old women may have more infanticide because due to marriage are likely to have another opportunity for reproduction if defects occur

Question 13

Marlowe

what hypothesis does it support

Answer 13

• Studied parental care of children less than 8 y/o in Hadza
• Have polygynous marriages, but divorce is very common resulting in serial monogamy and step parenting
• The less reproductively available women, the more paternal caring supporting Mating Opportunity hypothesis

Question 14

Parent-Offspring Conflict

parent/offspring perspective w/ 2+ offspring

Answer 14

• Inescapable in sexually reproducing organisms because parent and offspring are not genetically identical thus, what will maximize parental fitness will be different than what maximizes offspring

Parent Perspective: Because offspring have equal reproductive value and relatedness, they are equally valuable to my fitness. Offspring are excessively selfish and should value sibling more than they seem to.
Offspring Perspective: My own future will reproduction will do twice as much for my fitness as my siblings, so I’m more valuable

• High investment demand of current offspring reduces potential investment in future offspring
• If supplementation/weaning is late, mom pays more cost and infant gets more benefit. Vice versa if early (because mom can invest more in other kids)
• Table, Trophoblast, breast feeding, Hunter-gatherers, Perilloux

Question 15

POC Fitness table

NEED TO KNOW THIS!!

Answer 15

See slide 38

- Investing meal resources into offspring and the benefits to each

Question 16

Trophoblast

consequences of the behaviour

Answer 16

• Outer layer of cells of embryo attach to fertilized ovum and diverts nutrient/blood flow and occurs mom knows she is pregnant
• Trophoblast changes walls of spiral arteries so that mom loses control of these arteries and they ignore blood flow signal changes.
• Spontaneous abortion = 78% of fetal death
• A fetal tactic for controlling maintenance of pregnancy (may not be a fitness benefit in mothers eyes because they may want a spontaenous abortion for better prospects. Fetus will do everything it can to keep surviving though)

Conequences

• Blood flow no longer under control of mom. Only way she could cut off flow to infant is to reduce resources to herself
• Fetal cells manipulate blood cells, and this creates costs for mom (preclampsia can kill mom/shutdown kidneys)
• Direct access allows fetus to dump hCG into mom to manipulate mothers physiology (creating other manipulative effects)

Question 17

Human Chorionic Gonadotropin

Answer 17

• Fetus dumps these hormones into mom, these hormones keep uterus environment hospitable for development
• Also stimulates progesterone production
• Eventually mom produces enough progesterone to maintain pregnancy even if ovary stops producing
• HCG gives fetus a backup plan until mom (and some of her biology) is aware of pregnancy

Question 18

Breast Feding

Answer 18

• Replaces placenta as primary source of nutrition and immunity
• After 6 months, infant is bigger than they can intake calories (2-3k cal/day) - can lead to maternal depletion syndrome (progressive deterioration of moms physical status
• Carrying breast-feeding infant reduces labour efficiency and get harder to carry as they get older.
• Surpresses ovarian function and fertility (this is in offsprings best interest)
• Cost for mothers in poor condition/environments higher than for better

Question 19

POC Hunter-Gatherers

Answer 19

• In Africa, price of formula = 1/3 of family income. Women prolong breastfeeding and kin networks/social status can extend breastfeeding or take it over
• Zimbabwe: mother cannot stop breastfeeding without dad or mom-in-law consent (For dad and dads relatives, it’s in their best interest to prolong it)
  Mende: Extramartial affairs are believed to taint milk, women supplement earlier to not have infant malnutrition

Question 20

Perilloux et al. 2008

Answer 20

• POC can occur in adulthood over mating related behaviour
• P’s Perspective: want O to have a more conservative mating strategy to have higher quality mates.
  O Perspective: Hardwired to mate early as possible
• Parents/students rated how likely parents would have been to allow their child to engage in sexual activities
• O think that parents will be more permissive of mating scenarios
• Female O think their parents will be less likely to approve (and they are) - Daughter Protection Hypothesis: Because bad decisions for daughters is more costly.
• Doesn’t mean parents want their sons to have sex, they are just less prohibitive of it.

Question 21

Protectiveness of parents (based on sex) and sex of o

Answer 21

• Mothers are more protective of sons (because they know there son is theirs
• Fathers act differently and care more
• Sex difference in sons is paternal uncertainty.
  Daughters think their parents value attractiveness of their partner more than their partners actually do.

Question 22

Sibling Conflict

Answer 22

• Logical consequence of POC
• I’m twice as valuable as my bro/sis from my perspective
• Children with younger half sib report higher levels of conflict with their mothers
• Adult half sibs show less social investment in one another than full sibs
• Maternal half sibs have more social investment than paternal, more likely to be raised again.
• Co-residence can interact with genetic relatedness

Question 23

Birth Order
(what does it influence? and prenatal environment)

Answer 23

• Over-represented in prestige occupations (Astronaughts, presidents, nobel laureates) = first borns and more likely to get vaccinated
• Birth order influences: 1) differential ability of children to compete for PI. 2) differential allocation of care from parents
• See investment chart. First born and last born receive more investment because offspring eventually leave and allocation of resources can be more intense for last in order when everyone leaves
• Once a woman has given birth, cells of fetal genotype remain active in moms system for years which has effects that at still unknown.
• Maternal age influences quality of care given
• Fraternal Birth Order Effect

Question 24

Why can firstborns attain higher fitness?

Answer 24

1 ) More likely to survive adulthood as they have already survived first years when mortality is highest

2) likely to reproduce earlier, shortening generatino time
- Parents can realize reproductive payoff faster for firstborns than subsequents

• But birthorder is linked to family size (2 kid family you have 50% chance of being firstborn as opposed to 5-kid)
• May be an effect that they come from smaller families, not that firstborns have more prestigious qualities
• Firstborns are better at math, but when corrected for maternal age, the influence is gone

Question 25

Birth Order Hunter-Gatherer

Answer 25

• Preferential treament of firsborn children is widespread
• Camel-herding pastoralists (patrilocal, patrinlineal society
• Household wealth correlated to number of children especially for men (because inheritance goes to some)
• Birth order has a large impact on wealth and marriageability of men
• Firstborn has more resources available when they get married and thus can marry earlier
• Dowry for firstborn daughter is also higher (No advantage at any other point of birth order)

Question 26

Birth-Order Personality

Answer 26

• Firstborn daughters are more ambitious
• Firstborns tend to be more conservative (because traditional order suits them fine), laterborns derive fewer benefits from status quo and are more rebellious

Question 27

Middleborns

disadvantages and familial closeness

Answer 27

1 ) Middleborn US highschool boys rate parents as less supportive, reasonable and more punitive than first/last borns

2) Less likely to attend university and get less support from parents
3) Report more delinquent acts and less parental supervision

• Middleborns report parents as the person they are closest to MUCH less for men and women
• They report non-relatives much more
• Based on family size. The bigger the family, the less likely offspring will nominate mother (May imply they feel less closeness because they receive less resources)

Question 28

Using Kin Terms as Metaphors

Answer 28

• It exists in our literature
• Subjects filled out political attitude questionnaire, heard same speech with a few words changed “Kin/friends/fellow citizens” - then see if attitudes changed
• Overall kinship terms work, but not for middleborns.
• Middleborns find kin speech less effective than first/ast borns and find friendspeech best

Question 29

Fraternal Birth Order Effect

Answer 29

• Male pregnancies influence the development of subsequent male fetus
• The more older brothers a man has, the more likely he is to be gay
• No effect for sisters, parents ages or step/adoptive sibs
• Each additional brother increases odds by 33% and ~1/7 of homosexual men owes to FBO
• Maternal Immune Hypothesis attempts to explain this
• Homosexual males with older brothers weigh less (without more older brothers, no effect)

Question 30

Maternal Immune Hypothesis

Answer 30

H-Y antigens are produced by male, but not female fetus

• Mother produces antibodies to HY that enter fetal brain
• May prevent fetal brain from developing male-typical pattern
• Strength of immunization increases with each fetus

Question 31

POC Summary

Answer 31

• Birth order effects a by-product of sib conflict
• May result in stable personality styles
• Influences emotional closeness, responsiveness to kinship cues