Human sociobiology 2

1
Human sociobiology (2)

• MSc ACSB 2005/06
• Session 16

2
HSB vs competing explanations

• Kitcher Vaulting Ambition Chapter 9 Hypotheses
  Non Fingo
• Is conventional wisdom (EFP) equally good?
• SB predictions weak, or maths doesnt work
• Dickemanns prediction of upper-caste female
  infanticide requires an unrealistically high
  bridegroom price, and maths predicts male
  infanticide in the middle and lower castes
• Avunculate where childrens support is
  responsibility of the mothers brother, women
  should adopt the Calpurnia strategy

3
Why Mildred Dickemanns explanation of
infanticide among the Rajputs doesnt work

• See Kitcher, 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

4
Dickemanns explanation of Rajput infanticide
doesnt work (II)

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

5
Tibetan polyandry John Crook

• 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_gchildren)
• 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)

8
Tibetan polyandry (3)

• But is this the right approach?
• Assumes the Tasmanian Native Hen model
• Alternative model I exploitation of 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

9
Polyandry (4)

• Non-random allocation of family-sizes to farms
• Suppose
• Largest marriages on very 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 N. children will be
  misleading
• Cant perform the proper experimental study on
  humans - allocate marriages to farms at random,
  then look for a difference in average family size

10
Polyandry (5)

• Taxation system requires each separate family
  unit to be above a certain productivity
  increase the number of members until viable, or
  reclaim it into the unit from which separate off
• But kinship must increase stability of large
  family units, and youngest brothers can be
  exploited by kin (either elder brothers, or
  parents), so sociobiology can help 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 womans brother
  (childs uncle) will have a low but certain
  relatedness to the child via its mother (his
  sister/ half sister), and 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 an equation defining a
  paternity threshold below which men should invest
  in nephews/nieces, not 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 (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.
  Are women who do this following 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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More than one female strategy?

• Women may play a mixed strategy
• Differences between behaviour of women who score
  high vs. low on scale of sociosexuality
• Differences in womens preference between the
  period of high conception-risk and the rest of
  menstrual cycle. (Pill users resemble the latter)

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Pupil sizes and mate choices

• Tombs Silverman (2004) EHB 25, 221-228
• Expanded pupils enhance attractiveness in both
  sexes
• But some women prefer men with large pupils,
  others prefer medium pupils
• Large-pupil preference linked to womens tendency
  to select bad boys rather than nice guys for
  dates
• Suggests a strategy-differences among women in
  their response to the male attention/attraction
  implied by the largest pupil size
• Some evidence (UoE, unpublished) that in
  high-fertility part of menstrual cycle, large
  pupils preferred

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Womens rating of mens displays

• Gangestad et al. (2004) Psychological Science
  15(3), 203-207
• Men videoed in competitive date-choice context
  women see 1 min of video, rate man as for short-
  or long-term relationship
• Social presence composed, athletic, eye contact,
  no self-deprecation, no downward gaze, doesnt
  present self as nice guy
• Direct intra-sexual competitiveness e.g., slags
  off competitor, asserts superiority, not just
  himself, no laughter, doesnt say he has a nice
  personality
• Composite Sp-Dic rating peaked at day 11 of
  menstrual cycle, but only for short-term
  relationships

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Lonely hearts studies

• Huge literature on what men and women want in a
  sexual partner as shown by offers and
  requirements in personal ads
• Women ask for resources, offer good looks
• Men ask for good looks, offer resources
• Kindness, humour, etc., also important
• Bressler (2006) EHB (two papers) Humorous or
  non-H autobiographical sketches -gt men produce,
  women judge
• Women chose humorous males for relationships men
  preferred partners who appreciated their own
  humour, women preferred partners who produced
  humour sex difference less marked for short-term
  relationships and also for friendships

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Chat-up lines

• Bale et al (2006) PAID 40, 655-664
• 40 vignettes a man tries to open conversation
  with a woman which openings were likely to
  work?
• Humour, flattery, and blue remarks unlikely to be
  successful
• Openings that show off character, culture and
  wealth rated more likely to succeed
• See http//msnbc.msn.com/id/11333284/060214a

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Geoff Miller the mating mind

• Evolution of intelligence through sexual
  selection, not natural selection
• But why intelligence, rather than athleticism/
  another index of quality, for partner choice?
• Why are humour, kindness, and personality so
  important (to both sexes)?
• What forms of intelligence are sexually most
  appealing/ unattractive?
• Logic (Mr Spock)? Empathy? Verbal skills?
  Skill in making things? Creativity?
• Women want to make cads into dads, but not dolts
• Perhaps ask what is unpromising material as a mate

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Honest signals to opposite and same sex

• Risk-taking as a signal Farthing, 2005, EHB 26,
  171-185 risks were heroic, physical or from
  drugs
• Women preferred heroic risk-taker over h.
  risk-avoider as mate men less strong effect
• Men (not women) selected physical risk-takers for
  same-sex friendship
• J Diamond (RFTC p. 180) Kung-Fu kerosene
  drinking as a test of advanced grade kung-fu.
  JDs informant was grade 8 can single-handedly
  fight off 8 attackers. Alcohol, tobacco, etc may
  show up quality, and may be within-sex signals

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SB may not predict the most important social
processes

• Variation in societies needs explanation
• Not a close link between adaptation and success
  at the level of societies
• Early farming was linked to lower quality of life
  than for hunter-gatherers only replaced the old
  system at 1000 yards p.a., but impossible to
  revert once it had arrived (RFTC p. 163)

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J. Diamond Guns, germs and steel

• GGS follows up parts 4-5 of RFTC.
• Why was New Guinea (etc.) invaded and conquered
  by travellers from Europe, rather than Europe
  conquered by travellers from PNG (etc.)
• Role of disease, etc. in reducing ability of New
  World or Australasian populations to resist
  Europeans
• Different orientation of the continents
  facilitates/ inhibits spread of farming other
  skills
• Luck determines number of plant and animal spp.
  suitable for domestication and their utility,
  especially as beasts of burden
• 2º reduction in social complexity in Australian
  outback

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References

• Kitcher Vaulting ambition
• Betzig Human reproductive behaviour
• Miller The mating mind
• Diamond The rise and fall of the third chimanzee
• Diamond Guns, germs and steel