Human Sociobiology 1

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Human Sociobiology 1

• MSc ACSB module 2006/07
• SB week 6

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Contributions from animal SB ??

• Aid-giving explained by kinship/ inclusive
  fitness, reciprocation, (? reputation, etc.)
• Mate choice, mating strategies
• Parental investment, step-parents, sex ratio
  adjustment
• Life history strategies
• Evolved mental modules e.g. cheat detection
• Evolutionary analysis of man as a primate

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Changes since early HSB

• Helena Cronin The ant and the peacock
• Two separate puzzles for Darwin
• Early HSB emphasized IF, aid-giving, kin
  relations in warfare, etc.
• But we now know that IF is only one (?minor)
  factor accounting for animal cooperation
• In ASB and HSB, mate choice and mating strategies
  have become more sexy topics
• Even things such as jealousy that were originally
  explained in terms of sex difference in PI can be
  ?better understood in terms of mating
  opportunities

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Problems with HSB

• Kitcher (1985) Vaulting ambition
• HSB tries to explain too much. Predictions
• may trivialise important issues (rape, child
  neglect)
• legitimise bad behaviour, or appear to do so
• Are vague, are often changed if they dont work
  (dont definitively test theory), are poorly
  worked-out
• Buller (2005) TICS article and Adapting minds
• Poor-quality evidence needs higher standards of
  scientific argument
• Quibbles about details, many of them well-merited

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An evolutionary psychology of rape?

• Can sociobiology offer a useful perspective on
  sexual harassment and rape?
• Does taking this perspective justify'
  unacceptable behaviour?
• Wilson, FM (1995) Organisational Behaviour and
  Gender. McGraw Hill, Chapter 7
• Thornhill NW and Thornhill R (1997) An
  evolutionary analysis of psychological pain
  following rape 1. The effects of age and marital
  status. In Betzig, L. Human Nature. OUP,
  Chapter 24.
• Thornhill, R. (1997) Rape victim psychological
  pain revisited. Betzig, L. Human Nature, OUP,
  Chapter 25
• Thornhill Thornhill (1992) Behavioral and Brain
  Sciences, 15, 363-375 and 376ff.
• Thornhill, R Palmer, CT (2000) A natural
  history of rape Biological bases of sexual
  coercion. MIT press
• Class discussion later in the session

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Society-level characters do obey evolutionary
rules

• Mace Pagel (1995) Latitudinal gradient in
  density of N Amer languages PRSB 261, 117-121
• Gradients in (i) density of species pole (low) ?
  equator (high) and (ii, Rapoports rule) species
  geographic range (high?low)
• Similar trends in N Amer native languages trends
  confirmed as present separately in all 3 language
  families Amerind, Eskimo-Aleut, Na Dene

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Kinship aid in warfare

• Chagnon Burgos (in Kitcher, p. 307-315)
• In Yanomamo axe fight, CB say aid given by close
  kin of opponents
• But Kitcher makes a strong case that the
  differences are better explained by village
  loyalties, etc.
• Sahlins Use and abuse of biology makes
  distinction between human kinship systems vs.
  geneticists measures of relatedness

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Why is kinship so complicated?

• Chagnon (1982) Ch. 14 in Current problems in
  sociobiology ed. by Kings College Sociobiology
  Group
• Parents arrange marriages and seek liaisons which
  will maximise benefit to the family
• Because of different M, F generation time,
  complex relationship between relatives
• Men will re-define kinship (by changing way in
  which they speak of someone) to permit them to
  arrange beneficial marriages for their children

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Tibetan polyandry John Crook

• Crook Crook in Betzig et al. (ed) Human
  Reproductive Behaviour
• Wife with 2 husbands, typically brothers
• Farming in low-productivity environment
• Ideal is 3 males cultivate, herd, trade
• Farms passed down undivided to single family
• Crook sought explanation in inclusive fitness
  if family size from joint paternity is above a
  certain threshold, sharing a wife can be
  explained by IF
• p gt (2hm)/(h1),
• where m children in monogamy, p children
  in polyandry, and h number of husbands assumes
  all husbands have equal chance of fathering the
  offspring

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Tibetan polyandry (2)

• Mean family sizes for polyandry
• Major dwelling 1 2 3 4 mean
• 3.8 4.8 4.7 9
  5.2 poly
• Minor dwelling 2.0
  3.1 monog
• Benefit in fitness units (0.25no_of_grandchildren
  )
• Monog Polyandry
• Woman 3.3 4.3
• Man 3.3 1.9
• Crook assumes a Tasmanian Native Hen model of
  human polyandry

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Tasmanian native hen

• 2 males (brothers) breed with 1 female
• Experienced pair, alone 1.1 young
• Experienced pair, 1 helper 3.1 young
• Benefit from helping 2.0 young
• Helper (beta) is brother of breeder (alpha)
  achieves 1/3 of copulations
• r(helper) is (1/3).5 (2/3).25 .33
• r(breeder) is (2/3).5 (1/3).25 .42
• For helper, 2.33 (.66) is gt 1.1.5 (.55)
• For breeder, 2.42 (.84) is gt 1.1.5 (.55)

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Tibetan polyandry (3)

• But is this the right approach?
• Assumes the Tasmanian Native Hen model
• Alternative model I exploitation by family
• White Fronted Bee-Eater model
• Younger brothers in Tibet may have little
  leverage, so open to exploitation by parents/
  elder brothers
• Alternative interpretation II non-random
  allocation of families to good/poor farms
• Alternative explanation III society / taxation

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Polyandry (4)

• Non-random allocation of family-sizes to farms
• Suppose
• Largest marriages are arranged on poor farms
  (where 1- or 2-husband families cant survive)
• Smallest marriages on best land (where viable)
• Increase in offspring by adding extra husbands
  will be offset by the reduction in quality of the
  land so comparisons of number of children will
  be misleading
• Cant perform proper experimental study on humans
  cant allocate marriages to farms at random,
  then look at offspring vs. marriage size

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Polyandry (5)

• Tibetan taxation system requires each separate
  family unit to exceed a threshold productivity
  most add to the number of members until viable,
  or re-absorb it into unit from which budded off
  off
• But kinship must improve stability of large
  family units youngest brothers can be exploited
  by kin (either elder brothers, or parents), so SB
  helps us understand how these families work
• See also Barrett et al, Human evolutionary
  psychology, p. 224-234

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Societies with the avunculate are puzzles

• In societies showing this arrangement (MoBr
  societies), the mothers brother, not the childs
  putative father, is responsible for the childs
  support. Kitcher P299 ff.
• If women mate with many men, confidence that a
  child has been fathered by a particular male
  partner will be low.
• The mothers brother (childs uncle) will have a
  low but certain relatedness to the child via its
  mother (his sister/ half sister)
• This can justify the uncle, rather than the
  father, investing in its rearing
• If p is prob. that a womans child is sired by
  her husband, Kitcher derives p2 4p 1 lt 0
  (giving p0.268) as a paternity threshold below
  this, men should invest in their nephews/nieces
  rather than in their wifes children

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The avunculate (2)

• Kitcher considers the richest man in the society,
  then the next richest, etc. Each in turn is
  better to invest in nephews/nieces below this
  threshold
• But why does a woman not adopt the Calpurnia
  strategy
• offer the wealthiest man to guarantee his
  paternity (e.g., to be supervised by his female
  relatives) in return for his direct investment in
  her children
• this strategy would expand down the wealth chain
  once those at the top adopted it
• But EPCs indicate benefits of multiple-mating.
  Women who do this may follow a strategy to
  maximise the genetic diversity of the children,
  and guarantee survival of at least some in the
  face of epidemic disease or other biological
  hazards.

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Dickemanns explanation of Rajput infanticide
doesnt work

• See Kitcher, Vaulting ambition, p. 315
• Indian societies polygyny hypergyny
• Upper caste infanticide a striking fit to
  Trivers Willards predictions
• Problems (I) Logical
• Trivers-Willard model has no. of offspring
  constant, and offspring sex ratio shifts
• Dickemann has daughters killed but ?? are sons
  born to replace them
• Economic not reproductive costs. Daughters cost
  money to rear and to marry-off

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Dickemanns explanation doesnt work (II)

• Problems (II) Marriage and rearing costs
• For infanticide to be worthwhile, Kitcher shows
  that the bridegroom price must be
  unrealistically high (why not let daughters stay
  unmarried?)
• Infanticide works in the upper caste in model
  only if rearing/marriage costs are so high that
  male infanticide predicted in lower/middle caste
• Wealth, power and influence, not Darwinian
  payoffs, are key to understanding the cultural
  practice of infanticide

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Diamond Guns, germs and steel

• Jared Diamond on history of European expansion to
  America, Australia, etc.
• Why did small parties of Europeans conquer and
  displace native peoples?
• Diseases kill populations who are not immune
• Good luck with domestic animals and plants
  Eurasia is E-W continent, easy trade routes, use
  of horses in warfare
• Geography sets ground rules for evolution
  RFTC
• Of all our human hallmarks, the one that has
  been derived most straightforwardly from animal
  precursors is genocide RFTC

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Thornhill on Rape

• Can sociobiology offer a useful perspective on
  sexual harassment and rape?
• Does taking this perspective justify'
  unacceptable behaviour?
• Do men employ coercive sex when they are unlikely
  to attract a mate otherwise?
• Distress of victim (wrt age, type of sexual
  assault, physical injury) tracks risk of
  pregnancy loss of partners support
• Does evolutionary perspective provide a
  justification for this repugnant behaviour?

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References

• Helena Cronin The ant and the peacock
• Kitcher Vaulting ambition
• Betzig Human nature
• Buller Adapting minds
• Diamond The rise and fall of the third
  chimpanzee
• Diamond Guns, germs and steel
• Levine, N (1988) The dynamics of polyandry
• Levine Silk (1997) Current Anthropology, 38
  (3), 375-398 tibetan polyandry