L14- C+C in Humans

Evolutionary Psychology (sociobiology)-

• the study of the effects of genes on human behaviour

• has caused controversies in past e.g. Darwin’s theory

  • simplistic arguments

  • abuse of darwinism (social darwinism)- eugenics movement in late 1800-1960s, phylosophical justification for apartheid, etc.

  • motivation- don’t think about inclusive fitness when behaving

• talking about evolved behaviours consistent with some kind of adaptive functions

Menopause-

• life history theory→ natural selection should make soma (body) and germ (reproductive) function run out at the same time

• menopause→ loss of reproductive potential followed by long post-reproductive life

• isn’t a product of extended lifespan, same pattern is seen in current hunter-gatherers and historical populations

• few other species that experience this e.g.

  

• seen in one population of chimpanzees-

  • new population in West Africa found that female Ngogo live long after they stop reproduction, whilst other populations of chimps die at age of end of reproduction

    

Theories:

1. Mother hypothesis

   • Avoid risky reproduction and mortality in later life and ensure survival of existing offspring

2. Grandmother hypothesis

   • Kin selection – gain inclusive fitness by helping existing offspring to reproduce 

pre-modern population of Finns and Canadians (before modern contraception and medicine)

Mother hypothesis

• affect of mother’s death on fitness of offspring

• very little affect, slight reduction of lifespan on pre-weened offspring in Finland

• little affect of breeding success on offspring

  

  → no strong evidence for the mother hypothesis

• beyond weening age, the care from mother is compensated for by other family members

Grandmother hypothesis-

• additional number of granchildren in realtion to lifespan of grandmother after menopause

• the longer a grandmother stays alive, the more offspring their children have

• 2 extra grandchildren for every 10 years post-menopause

  

• having a mother alive means:

  • higher fecundity

  • higher lifetime reproductive success of offspring

  • more kids if grandmother remained local

  • earlier reproduction

  • shorter intervals between successive births, less effect with the more children they have

  • increased survival to 15

    

  → grandmother can relieve burden on mother

• similar results found in orchas→ surviving matriach ahs a positive effect on survival on grandoffspring, especially grandsons

• hypothesis grandfathers are less effective at this, no sig effect of grandfather alive or dead on lifetime reproductive success of offspring, survival probabilty is slightly lower

  

• analysis- fitness effects of grandmothers

  • argue kin selection of helping as a grandmother did not outweigh continued reproduction

  • suggest menopause was also driven by reproductive competition between mothers and daughters/daughters in law

  • Finn population-

    • timing of reproduction by grandmothers and children- nearly no overlap→ there is a mutually exclusive reproductive activity

    • offspring survival- overlap means decrease in offspring survival- negative effect on productivity

      

→ grandmother effect is true but with the added conflict

Cooperative Breeding

• historical Finn population-

  • do unmarried siblings act as helpers? NO

  • do aunts and uncles help? NO

  • had lots of co-breeding (siblings marrying and living in same house)- did co-breeding wives positively affect offspring? NO, if they overlapped, there was a negative effect

    

→ no evidence for cooperative breeding in historical Finn populations

• categorised parental care patterns across societies:

  • some societies have strong evidence that individuals other than parents provide significant amounts of offspring care

  

• is the pattern of care influenced by ecology?

  • Cooperative care more frequent in unpredictable climates with low rainfall and low temperatures, and when starvation risk is low.

• males typically have higher reproductive potentials than females

• highest reproductive successes:

  

• mating system diversity→ in 849 societies:

  • 0.5% are polyandrous

  • 16% are monogamous

  • 84% are polygynous

  → most societies have some level of polygyny

Polyandry:

• very rare

• most investigated in Buddhist communities in Kashmir+Tibet

  • usually have 2-3 co-husbands per wife, usually brothers

  • in typical community→ 33%of males aged 10-59 in polyandrous marriages, 31% of females aged 20-59 unmarried

  • big effect on reproductive potentials→ 0.7 children per unmarried woman, 3.3 children per married woman  

• is influenced by 2 factors:

  • environment→ live in harsh, high altitude environments, only agriculture is possible in small community deltas→ maintaining integrity of units of land

    

  • culture→ buddhism, some sons were dispatched to the monastry, usually second son

    • number of children produced by brothers, sisters, grandfathers if they dispatched a son to be a monk

    • sons- 0 monks, low fitness, 1 or more sent off

    • sisters- 1 or more monks dispatched to monestry- high reproductive success, same

    • fathers- higher when dispatching son

      

• are so stable because

  • kinship→ marrying brothers reduces conflict

  • age hierarchy→ second son is often dispatched as they are the most likely to compete for paternity

Monogamy-

• common in hunter-gatherer and western societies

• is not strict due to:

  • extra care paternity- ~1% of offspring

  • serial monogamy

    • average number of children according to number of spouses

    • more marrigages with women had no effect but men had a sig increase with number of children

      

Polygyny-

• norm in most cultures

• e.g. mormons, ishmael the bloodthirsty

• resource defence polygyny

• polygyny is higher in wealthier men- positive correlation

• pattern of inheritance of wealth and financial transactions at the time of marriage- european- wifes family to pay a dowry to groom, grooms family pays brides family is more common- more common as polygyny increases- almost always occurs, affects the way resources are inherited- fairly even in monogamy, polygynous is predominantly by sons

used dataset from pacific and SE Asia

• classified every society according to 4 levels of social complexity

  • acephalous- no head person, families living togethe

  • simple chiefdom→ single chief

  • complex chiefdom→ multiple layers below chiefs

  • state→ civil service

• investigated

• evolution of language across the societies, how transitions of social complexity mapped on

• asked if these transitions were all equally likely

  

  • increases in political complexity→ occur in sequential jumps, no big transitions

  • decreases in political complexity→ some are sequential but there are also major jumps in societal structure- were typically associated with major environmental destruction by people e.g. Easter Island

    

→ ruining the environment can get a total collapse in society