Evolution of Intelligence Social Intelligence Hypothesis

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Evolution of Intelligence - Social Intelligence
Hypothesis

• Is it biologically plausible to predict human
  brain and group sizes from nonhuman primate brain
  and group sizes, as Dunbar does?
• If Dunbars views are taken on trust, what novel
  predictions can be made in psycholinguistics and
  social psychology?

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Overview

• Intelligence in primates and humans
• Measurements of brain size, theories and
  development of structures
• Social intelligence hypothesis empirical
  evidence from studies on primates
• From primates to humans developmental trends in
  childrens social behaviour
• Impact on social psychology and
  psycholinguistics
• Criticism the spotted hyenas
• Discussion

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Intelligence and brain size

• Primates have unusually large brain compared to
  other animals
• Brain size as indirect measurement of
  intelligence - allometric scaling
• Human brain 3 times larger than apes and
  monkeys increase of more than 250 through 3
  million years
• Enlarged brain related to high costs energy,
  metabolism, prolonged childhood and development
• How and why possible advantages of big brains?

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Theories

• Sudden genetic change jump in evolutionary
  development
• Ecological problem solving and physical
  environment linking species brain size and its
  ecological niche tool use, hunting, foraging,
  food processing
• Metabolic hypothesis efficiency of mothers
  metabolic turnover determines neonatal brain size
• Sexual selection hypothesis mate choice of
  females for increasingly intelligent males
  selective pressure acting on cognitive abilities
• Social brain hypothesis or Machiavellian
  intelligence did sociality cause modern
  intelligence?
• Theories not mutually exclusive ...

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Its not the brain size Dunbar Barton (1997)

• Encephalisation brain size relative to body size
• Effects of selection pressures on body and/ or
  brain size difficult to distinguish
• Spatial cognition hypothesis storage of food,
  spatial ability and the hippocampus
• Evolutionary cognitive neuroscience beyond brain
  size - differentiating neuronal structures
• Neocortex

• Hippocampus of human brain

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Neocortex

• Increased brain size in primates due to neocortex
  enlargement varies greatly across species
• Neocortex is intelligent part of mammalian
  brain
• Intelligence, sensory information, planning
  behaviour (speech), social manipulations,
  tactical deception
• Neocortex ratio volume of neocortex divided by
  brain volume more exact than Encephalisation
  Quotient Dunbar, 1992)
• Neocortex ratio positively correlated with larger
  group size in primates

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Social Intelligence Hypothesis Dunbar and
Barton, 1997

• Large brains and distinctive cognitive abilities
  of primates evolved through Machiavellian
  strategies of social competitors
• Selection pressure for achieving social success
  use of deception, manipulation, alliance and
  exploitation
• Social success translates into reproductive
  success
• Neocortex ratio correlated with group size
  larger neocortex in animals living in larger
  social groups
• Group size as proxy of species social complexity
• Confounding ecological factors diet, home range
  size, activity timing

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Continued... Social Intelligence Hypothesis

• Neocortex ratio unrelated to environmental
  complexity after controlling for body size
• Social complexity increases with group size
• Cognitive constraint group fragments when size
  increases past complexity limit set by neocortex
• Exists in other species bats carnivores, and
  cetaceans

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From primates to humans

• Extraordinary cognitive competencies sense of
  self, language, theory of mind (ToM)
• Human neocortex neurons more interconnected
  allowing for greater ability to integrate
  information across modalities (parallel
  processing)
• Human neocortex larger than primates in areas
  that support social competencies, which are
  unique to humans
• Extended childhood opportunity for complex
  development and acquisition of social skills

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Childrens social networksHenzi et al. (2007)

• Individuals ability to interact limits group
  network size mechanical constraints of human
  speech?
• Examining childrens conversational group and
  clique sizes as indicator of cognitive ability
• Cognitive demand of conversation developmental
  trend between ages 3 and 13 years
• ToM promoting social skills and interaction
• Clique size increases with age from 2 to 5
• Relationships remain similar, numbers increase
  cognitive constraints on multiple social
  interactions not single conversation
• Constraints do not result from speech but from
  cognitive demand in maintaining coherent groups

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Novel Predictions

• The potential impact on psycholinguistics and
  social psychology

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psycholinguistics

• Study of psychological and nuerobiological
  factors that enable humans to acquire, use and
  understand language. E.g. Chomsky.
• What cognitive processes enable the generation of
  syntactically and semantically valid sentences
  and the understanding of utterances and text?

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social psychology

• Study of the interplay between peoples internal
  mental states and behaviours and the influence of
  others.

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Dunbar psycholinguistics

• (1) The fact that language can be interpreted as
  fulfilling the same role as social grooming
  suggests that, rather than being the selective
  factor driving brain evolution, ecologically
  related information-exchange might be a
  subsequent development that capitalised on a
  window of opportunity created by the availability
  of a computer with a substantial information
  processing capacity. (Dunbar, 1993).

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Dunbar psycholinguistics

• I.e Language, often seen as a driving
  evolutionary factor in the expansion of the human
  brain, was itself enabled by a human brain which
  had been expanded by the real driving factor the
  selection pressure of social living.

• Objection
• Language is designed specifically for the serial
  production of propositional communication, it is
  a modular ability and cannot just be a faculty of
  general purpose computer. (Pinker Bloom, 1990).

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Dunbar psycholinguistics

• Difficult scenario to reverse engineer.
• Invert? selective pressures for language
  evolution related to interpersonal communication
  which solved the problem of social grooming in
  large groups? (Corballis, 1993).
• Proto-language as sign-language? Tool explosion
  the result switch to vocal communication? Support
  for Dunbars social grooming hypothesis?
  (Corballis, 1991/92/93 Pfeiffer, 1985).

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Dunbar psycholinguistics

• Dunbar Language evolved as a more efficient
  means than grooming of maintaining group
  cohesion.
• Deacon Just another just-so story.
• language makes X more efficient, therefore
  selection for X explains the origins of language
  (Deacon, 1993).

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Dunbar psycholinguistics

• X could stronger social cohesion.
• X could more efficient foraging.
• X could better transmission of past
  experiences to offspring.
• X could more efficient communication.
• Human brain size, neocortical size and language
  evolution will probably be linked, but Dunbar has
  picked too simplistic a brain-ecology
  relationship to account for this. (Deacon, 1993).

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Dunbar psycholinguistics

• There are three kinds of lies lies, damn lies,
  and statistics. (Mark Twain).

• Is it an error to assume that human
  brain-language evolution is merely an
  extrapolation of some general evolutionary trend?
• Could language be the result of unique selection
  pressures? If so, then Dunbar et. al. are
  failing to carve the issue at the joints.
  Questions need to be rethought.
• To rethink these questions would require moving
  far beyond brain-ecology statistics. (Deacon,
  1993).

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Dunbar psycholinguistics/social psychology

• Two testable hypotheses
• The social bookkeeping effect of Language would
  seem to be double edged cheaters could use
  language to decieve others and cause group
  disentegration, just as much as it would allow
  non-cheaters to keep track of such behaviour.
• Cheaters may prosper in a certain level of
  anarchy. ( Dugatkin Wilson, 1993).

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Dunbar psycholinguistics/social psychology

• (I) Within groups language may favour cheaters.
• (ii) Between groups language may favour cohesive
  groups.

• So did between-group competition play a major
  role in Pleistocene times (the formative years
  of human psychology)?
• Were Groups acting in a co-ordinated manner
  generally the winners?
• Do all or most cultures display, or have historic
  traces of group level rules to deal with cheaters
  who use language to decieve others and create
  group level anarchy?

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CriticismHolekamp (in press)

• Social intelligence hypothesis empirically
  supported but restricts understanding of
  evolution and of intelligence
• Evidence from spotted hyenas

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Spotted Hyenas and others

• Resemble primates in social behaviour, social
  structure, cognitive and perceptual abilities,
  nepotism
• Cognitive differences in flexibility, object
  interaction, learning
• Common ancestors 90 to 100 million years ago
  both species deal successfully with social
  complexity
• Brain size of mammalian carnivores and prey
  covaries through geological time
• Bears more flexible behaviour in solitude
• Occurence of social learning in primates not
  related to group size among primates
• Other reasons than social complexity caused
  development of cognitive abilities
  environmental challenge

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Conceptual criticisms

• Just what is intelligence anyway?
• Searching for the explanans without a proper
  understanding of the explanandum?

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Conceptual criticisms

• Explanadum intelligence.
• Rather than getting bogged down in the
  philosophical quagmire of defining
  intelligence, let ussimply treat it as
  whatever mechanisms enable an individual to take
  into account the complexities of social or
  other life and devise appropriate responses
  (Byrne Whiten, 1997).

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Conceptual criticisms

• Is Byrnes Whitens definition circular it
  might seem so
• The explanans (social factors) being cited to
  explain the explanadum (social intelligence). But
  surely this is the very point at issue?
• A quagmire that must be crossed (or at least
  attempted).

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Conceptual criticisms

• It isan unnecessary distraction to search for a
  general property intelligence that is
  unconnected with specialisations for particular
  ways of life. (Barton Dunbar, 1997).
• Yes, the mind is (to some extent at least)
  modular. Yes, intelligence is unlikely to be one
  module. But it does not follow that intelligence
  does not constitute a kind (however that is
  understood) or is not a general property. To
  boldly assert so is, again I think, to risk
  assuming one of the key points at issue.

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Conclusions

• Primates have larger brains and show greater
  social complexity
• Implications Psycholinguistics / social
  psychology
• Developmental trend in humans regarding social
  interaction
• Two questions remain
• Does intelligence really have a social origin?
• What are possible alternatives of explanation?

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