ACSB Workshop 3

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ACSB Workshop 3

• Fluctuating Asymmetry (FA)
• Geoffrey Miller
• Evolutionary Psychology vs. Critics

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What is Fluctuating Asymmetry?

• Fluctuating Asymmetry (FA) - deviation from
  perfect symmetry in bilateral traits that are
  symmetrical at the population level.
• Biologists typically measure Developmental
  Instability (DI) with fluctuating asymmetry (FA).
  

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Developmental Instability (DI)

• Imprecise expression of phenotypic design due to
  perturbations during development. The source of
  these stresses can be genetic (e.g. random
  mutations) or environmental and are presumed to
  cause random errors in development, which
  compromise optimal phenotypic expression.
• Relevant environmental stresses could be toxins,
  pathogens (any disease-producing agent
  (especially a virus or bacterium or other
  microorganism)), nutritional deficits, and
  temperatures to which an organism is not adapted.
• An individual's developmental instability is a
  function not only of these stresses, but also of
  its ability to compensate for them (e.g. its
  ability to resist pathogens)

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FA continued

• When an organism is well-adapted to its
  developmental environment (i.e. possesses
  developmental stability), development of
  bilateral characters that are symmetrical by
  design will be, on average, more symmetrical.
• By contrast, exposure to developmental
  perturabations and an inability to resist their
  effects may result in developmental anomaly and
  subtle structural studies show that FA increases
  in populations exposed to environmental stressors
  such as extreme temperatures or toxins.
• Some studies link FA with inbreeding, which
  exposes recessive deleterious mutations and
  reduces heterozygosity. (Woolf Markow, 2003)
• Furthermore, on average across animal species, FA
  is negatively associated with fitness variables
  such as longevity and fertility

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Directional Asymmetry

• FA is not to be confused with directional
  asymmetry (DA) which refers to features in which
  a population of organisms shows a consistent
  structural or functional bias for a particular
  side of the body (e.g. placement of heart and
  number of lobes in the right versus left lung).

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Linking FA to Intelligence

• Many studies have been conducted that link FA to
  general intelligence.
• Prokosch, Yeo and Miller (2004)
• Thoma, Yeo, Gangestad, Halgren, Sanchez and
  Lewine (2005)

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Prokosch et al.

• Predicted that there was an overlap between FA
  and general intelligence.
• Intellectual test with higher g-loadings (which
  require a higher level of general intelligence)
  should show higher correlations with a composite
  measure of body symmetry.
• 78 young males
• Measured for left/right symmetry at 10 body
  points
• Performed 5 cognitive tests (of differing
  difficulties)

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Prokosch et al.s results

• Significant relationship between each tests
  ranked order of difficulty and its body symmetry
  association.
• They conclude that general intelligence is a
  valid indicator of general developmental
  stability and heritable fitness which may partly
  explain its social and sexual attractiveness.

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Thoma et al.

• Predicted that DI affects intelligence through
  effects on cortical size.
• 19 males measured for
• Fluctuating Asymmetry (FA)
• Cortical Volume
• General Intelligence

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Thoma et al.s results

• Both FA and cortical volume significantly
  predicted general intelligence but were not
  significantly correlated themselves.
• Concluded that developmental instability appears
  to affect general intelligence through pathways
  largely independent of cortical volume.

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How is FA linked to human intelligence?

• Soit seems that both general intelligence and
  body symmetry are fitness indicators.
• Traditionally, physical fitness indicators (like
  body symmetry in these studies) form a standard
  part of sexual selection theory.
• Miller argues that the psychological traits (like
  general intelligence) are also part of a sexual
  selection strategy.

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Geoffrey Miller

• Evolutionary Psychologist
• Obtained PhD from Stanford University in 1993
• Wrote book The Mating Mind how sexual choice
  shaped the evolution of human nature
• Currently at the University of New Mexico

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Millers views

• Evolution also driven by sexual selection.
• Sexual selection important in human mental
  evolution.
• Evidence comes from such areas of research as
  human mate preferences and courtship behaviour.
• Evolution of the human brain can be explained
  through runaway sexual selection.
• Based on Fishers runaway process

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Fisherian runaway process

• Fishers runaway process is driven by the
  genetic variation between sexual traits and
  sexual preferences in offspring which arises
  through the sexual choices their parents made
  (Miller, 2001)
• Peacock example.

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Peacock example

• Imagine population of birds with short tails
• Males contribute nothing to raising offspring
• Females choose any male they want even a male who
  has already been chosen by many other females
• Tail length is variable (all biological traits
  show variation)
• Suppose some of the females become attracted to
  tails that are longer than average (i.e.
  selection)
• Choosy females who prefer long tails mate with
  long-tailed males producing longer than average
  tailed sons
• Non-choosy females mate randomly with
  average-tailed males producing sons with mediocre
  tails
• The average tail length has increased in this
  population due to sexual selection through mate
  choice (the genes for long tails have spread)

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Peacock example cont.

• Offspring of choosy females will inherit genes
  for the sexual preference of long tails as well
  as the long tails Fishers runaway process is
  driven by this genetic correlation between sexual
  traits and sexual preferences and offspring,
  which arises through the sexual choices their
  parents made
• Miller applies this to evolution of human brain
  (substituting bird with hominid and long
  tail with creative intelligence)

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Major Problem with Runaway

• Runaway would predict large sex differences in
  creative intelligence and possibly brain size
• Male human brains on average only 100 cubic
  centimetres larger than female
• No sex difference in g-factor (IQ test
  performance)
• Must have been form of sexual selection that
  could work given mutual mate choice.

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Fitness Indicator Theory

• Sexual ornaments are costly and so are reliable
  indicators of fitness.
• Mate choice is a method for enhancing
  anti-mutation effect, by favouring sexual
  partners who carry 'good genes.
• Human brains good fitness indicators.

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Evolutionary Psychology vs Critics

• A main critic David Buller
• April 2005 - Adapting Minds Evolutionary
  Psychology and the Persistent Quest for Human
  Nature (Bradford Books)
• June 2005 - Evolutionary psychology the
  emperors new paradigm (TCS)
• November 2005 Responses by Tooby Comsides on
  cheater detection, Buss on sexual jealousy, and
  Daly and Wilson on step-children at risk (TCS)

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What is Evolutionary Psychology?

• Buller distinguishes between evolutionary
  psychology and Evolutionary Psychology
• Evolutionary psychology field of inquiry
• Evolutionary Psychology - a paradigm akin to
  Newtonian mechanics, consisting of interwoven
  theoretical claims, methodological commitments,
  and empirical results.

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What is Evolutionary Psychology?

• When evolutionary psychologists refer to "the
  mind", they mean the set of information-processing
  devices, embodied in the human brain, that are
  responsible for all conscious and nonconscious
  mental activity, and that generate all behavior.
  What allows evolutionary psychologists to go
  beyond traditional approaches in studying the
  mind is that they make active use in their
  research of an often overlooked fact That the
  programs comprising the human mind were designed
  by natural selection to solve the adaptive
  problems faced by our hunter-gatherer ancestors.
  It leads one to look for programs that are
  well-engineered for solving problems such as
  hunting, foraging for plant foods, courting
  mates, cooperating with kin, forming coalitions
  for mutual defense, avoiding predators, and so
  on. Our minds should have programs that make us
  good at solving these problems, whether or not
  they are important in the modern world. Leda
  Cosmides

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Cheater Detection

• Reciprocal altruism (the mutual exchange of
  fitness benefits) creates selection for cheaters
• The evolution of cheaters selects for the ability
  to detect cheaters.
• Evidence
• Wason selection task
• There is a content effect subjects perform best
  when they are reasoning about violations of
  conditionals that express social contracts
• Subjects ignore logic when the cards representing
  the correct solution differ from those
  representing, they choose cards that represent
  cheating. Subjects do not apply logical
  principles in solving social contract selection
  tasks but simply focus on whether someone has
  accepted a benefit without fulfilling an
  obligation

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Cheater Detection (Bullers Criticism)

• Differential performance might come from the
  difference between conditionals that express
  arbitrary vs. practical relationships.
• The idea that subjects ignore the logic of
  conditionals falsely presupposes that changing
  the wording of conditionals in selection tasks
  changes how subjects mentally represent their
  logical forms - rather subjects could have simply
  selected the logically correct cards relative to
  a sensible interpretation the problem.

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Sex Differences in Jealously

• Busss research argues jealousy evolved as an
  emotional alarm that signals a partners'
  potential infidelities and causes behavior
  designed to minimize losses of reproductive
  investment.
• For males, females sexual infidelities
  potential fitness costs of investment in another
  males offspring.
• For females, Males emotional involvement with
  another woman fitness costs in the form of lost
  parental resources.
• Evidence
• Sex difference responses to infidelity dilemmas
• Men more distressed by the thought of a partners
  sexual infidelity than emotional infidelity.

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Sex Differences in Jealousy (Bullers Criticism)

• To confirm hypothesis it needs to be shown that
  men care more about sexual infidelity than they
  do emotional infidelity, not that they care more
  than women do about sexual infidelity.
• Studies show that males exhibit greater
  reactivity to imagining events with sexual
  content than to imagining events with emotional
  content.
• Busss questionnaire results are confounded by
  males greater reactively to sexual than to
  emotional scenarios.
• Bullers proposal sex difference is not due to
  evolved design features but sex-typical, learned,
  situationspecific beliefs about the likelihood
  that sexual infidelity will lead to abandonment.

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Discriminative Parental Solicitude

• Based on Daly Wilsons research on evolved
  mechanisms of parental love specific to genetic
  offspring.
• Evidence
• (20 yrs. of research/1-year study in Canada)
  Children living with step parents more likely to
  be maltreated than children living genetic
  parents. Step children at greater risk because
  inhibition against the use of dangerous tactics
  in conflict is not triggered.
• Bullers criticisms
• His analysis of cases in a National study found
  risk of living with a stepparent significantly
  lower than Daly Wilson report.
• Definition of maltreatment too broad (includes
  things such as failing to secure child in seat
  belt).
• Results skewed by reporting bias against
  step-parents in official records confounded by
  the fact that not all not all child maltreatment
  fatalities are officially reported.

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Bullers conclusions

• Although the Evolutionary Psychology paradigm is
  a bold an innovate explanatory framework, I
  believe it has failed to provide an accurate
  understanding of human psychology from and
  evolutionary perspective.

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Questions

• How and why is human fluctuating asymmetry
  linked to human intelligence?
• Do you find Millers theories on the emergence of
  intelligence through sexual selection plausible?
• Which side wins the debate about the evolved
  architecture of the human mind evolutionary
  psychologists, or their critics?