Evolution and Family Life

Sex and reproductive variance:Males: bigger gamble; hi risk/hi rewardFemales: better odds, lower payoff

Trivers/Willard Hypothesis

• Good conditions: invest in boys• Not so good conditions: invest

in girls• Humans?

– Medieval Portugal church records – more boys conceived during years when rains were good (Jolly, 1999, p. 122)

– High income mothers breastfeed sons more than daughters, vice-versa low income.

– IBI longer for hi income after son; vice-versa for low income

– However, other contemporary studies have found mixed or negative results

Primate infanticide

• Sara Hrdy: Langur Monkey infanticide• Also documented in lions and gorillas. • New male has limited time as alpha, no time to spend on non-

genetic offspring.• Adaptive value of female promiscuity: “seeds of confusion”

theory

©John Wiley & Sons, Inc. 2007 Huffman: Psychology in Action (8e)

Risks of step-parenting. Note: Violent step parents represent less than 1% of step families

• Cross-culturally (60 different societies; Daly & Wilson, 1988) most common reasons for killing or abandonment of newborns/infants:

• Questionable paternity; low reproductive value of infant (weak, sick, abnormal; poor maternal circumstances (unmarried, little family/social support; poor resources)

Birth vs. step children: education, health; nutrition

• Anne Case – economist at Princeton Plight of Cinderella (children and step

mothers)• Sig decrease in food expenditure when

non-bio mother in home• Children raised with non-bio mother sig

less educational attainment compared to bio mothers

• In mixed families, exclusively non-bio offspring that suffer reduced educational levels (see graph left)

• Non-bio mother: fewer visits to doc, dentist; reduced expenditures on fruits, vegetables, milk, more on alcohol, tobacco.

Sibling rivalry

• Mom is equally related to all her offspring

• Sibs are 100% related to themselves; only half (genetically) related to each other

• All things being equal (which often they aren’t) Mom has natural incentive to be “fair” to offspring

• Each sib has incentive to extract more resources from Mom then sibs

• “That’s not fair”

Sexually Dimorphic Maturation Rates

• Put simply – girls mature faster than boys. Why?• Females: Secondary sexual development

precedes gametogenesis (fertility); they look sexually mature before they are fully mature (probably more exaggerated in ancestral past then today, in most traditional societies there’s 2-3 year period of infertility after onset of secondary sexual traits)

• Boys: vice-versa• 14 year-old boy vs. 14 year old girl

Sexually Dimorphic Maturation Rates

• Males: Evolved divergent mating strategies: Early maturing – Alpha strategy; more short-term mating opportunities. Late maturing -- stealth strategy; sexually fertile but physically non-threatening.

• Females: “Practice” for mothering skills• Evidence mixed: Faster maturing boys = higher status, more popular,

slower maturing boys = more creative• Girls do more babysitting, child care, but does this mean maturation rates

selected for this purpose, jury still out.

Future stability and female maturation rates

• K vs. r reproduction strategies: unstable future – live fast, reproduce early and often (r)

• Factors related to faster maturation rate in human females: (1) domestic instability and stress; (2) father absence; (3) lack of grandparental figures, esp grandfathers; (4) economic deprivation.

• Male investment unreliable; reproduce early while familial support present

Sex ratio, poverty, and reproduction• Operational sex ratio: ratio of sexually active males to sexually receptive females. • <1; more females than males; intense female mate competition. Few investing

males; marital instability; more single moms; promiscuity, etc • >1; more males than females; intense male mate competition. Low status males

lose out; greater marital stability; higher crime.

For lower socio-eco females (dashed and dotted lines) as osr decreases (fewer males) birth rate increases for younger women. But higher s-e women have lower birth rate at younger ages as osr decreases and higher birth rate at older ages. With few investing males, poor women “speed up” life history; rich women “slow down.”Ref: Chipman & Morris, 2013 study

Crazy Bastard Hypo

• Young male propensity for risk-taking: signal of formidabilty.

• Signal to whom? Male rivals and allies• Males who take risks are perceived as taller,

bigger, more muscular more prone to violence. • Turn off to females as long-term mate, but may be

desirable as “protector” in dangerous environment.

• Absence of fathers usually produces more violence among boys. Does propensity toward risk taking increase if boys do not see many older male role models around?

• In other words, where there is long-term mating (evidenced by fathers) a boy's mating strategy shifts toward attracting long-term mates and thus reduced risk-taking.

• Self-Reinforcing Cycle: violent social context -> risk taking males for allies -> less long term mating -> female preference for formidable male (genetics, protection) -> more risk taking -> more violence

Parental Grief

• Correlates with reproductive value curve for children more so than just age.

• Tends to peak at early adolescence. Max investment at threshold of reproductive payoff.

• Matches life history pattern of traditional hunter-gatherers, more so than contemporary life history curves.

Demographic Transition

• DT: Wealthy countries have below replacement birthrates

• Evo paradox. Why?• Greater investment per child

to maintain status• Status seeking conflicts with

parental investment• However, in long run higher

investment reduces fitness!• Genetic/personality factors

important: Extro males and agreeable females more fertile

• High status males more fertile; high status females less fertile.

Religion & Fertilitysource: last three slides see*

Data Source: Dominik Enste, Institut der deutschen Wirtschaft Köln 2007

Worship Attendance Adults / No. of Children 82 Nations & Germany

World Value Surveys 1981 - 2004, IW 2007

1,661,8

1,67

2,012,23

2,5

1,98

1,441,39

1,78

11,21,41,61,8

22,22,42,6

never onHolidays

once perMonth

once perWeek

> more often

Children Germany Children globally

Swiss Census 2000Denominational category

(CFR) Births per woman

% academiceducation

% higher occupational class

Hinduism* 2,79 (1) 17,0% (12) 7,4% (14)

Islam* 2,44 (2) 11,4% (15) 6,1% (15)

Jewish 2,06 (3) 42,7% (1) 42,4% (1)

Other (smaller) Protestant 2,04 (4) 20,1% (5) 19,2% (6)

New Pietism / Evangelical 2,02 (5) 19,2% (6) 17,9% (8)

Pentecostal 1,96 (6) 17,1% (11) 15,7% (10)

Other (smaller) Christian 1,82 (7) 39,1% (2) 31,8% (2)

Didn’t answer 1,74 (8) 19,1% (7) 5,3% (16)

Christian-Orthodox* 1,62 (9) 18,0% (10) 9,8% (13)

Swiss Average 1,43 19,2% 19,6%Buddhist* 1,42 (10) 20,3% (4) 13,4% (11)

Roman-Catholic 1,41 (11) 16,8% (13) 18,5% (7)

New Apostolic 1,39 (12) 13,9% (14) 17,6% (9)

Reformed Protestant 1,35 (13) 18,9% (8) 22,2% (4)

Yehova’s Witnesses 1,24 (14) 6,8% (16) 11,2% (12)

Christian-Catholic 1,21 (15) 18,4% (9) 22,2% (5)

Non-affiliated 1,11 (16) 30,6% (3) 26,7% (3)

r / Spearman Rank Correl. 0,054 -0,269

Religiosity is offering POTENTIALS to culturally diverse, reproductive strategies

We still found NO demographically successful non-religious population!

Hutterites, Haredim, Old

Order Amish etc.

Shakers

Non-Affiliated

USA, China, France,

Sweden, Austria etc.

*Why are the Non-Religious lacking ChildrenExploring the Evolutionary Adaptivity of Religion

Dr. Michael Blume( www.blume-religionswissenschaft.de )

„Philosophical Anthropology of Religion“, Wuppertal University, March 2014