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Social and Technical Forms of Primate Intelligence

Richard W. Byrne in 'Tree of Origin: What Primate Behaviour Can Tell Us about Human Social Evolution'

Notes by Georgina Holmes




Tree of Origin: What Primate Behaviour Can Tell Us about Human Social Evolution


Social and Technical Forms of Primate Intelligence

by Richard W. Byrne


How did our cognition and intellectual capacities evolve?

Role of Comparative Biology

  • Behaviour of ancient ancestors hardly preserved archaeology

  • Behaviour of modern living species can provide an insight

  • We can look at:

  1. What form does a particular behaviour take?

  2. The functions of a particular behaviour now?

  3. Under what conditions is a particular behaviour seen?

  4. How is the behaviour related to the environment?

  5. How does the behaviour vary?

Relatives have evolved as much as we have since divergence

  • Modern primates they are not perfect prehistoric ape replicas

  • Two popular but wrong theories of using comparative biology:

  1. 19th Century: Great Chain of Being

    • Belief that studying modern primate is direct way our ancestors were like

    • View that monkeys evolved into apes evolved into humans

    • Ontogeny recapitulates phylogeny

  2. 20th Century: Radical Behaviourism

    • Belief that all species equal so rat can be used to compare with humans rather than ape

    • But if all species equal why need comparison

    • Claims that language sets humans apart


  • Both theories are overly simplistic

  • Language cannot be acquired suddenly, it is so complex it must have roots in other animal cognition

  • Capacities of all animals are not equal:

  1. Monkeys show more complex behaviour than most mammals

  2. This ability results from an enlarged neocortex that allows rapid learning

  3. Great apes demonstrate some understanding of intentions and causes.

  4. This comprehension is based on an ability to perceive, and to build, complex novel behaviour

What do we need to consider to answer evolutionary questions?

1. Function of evolved trait

  • Selection pressure = environmental challenge

  • Environmental challenge met by aptitude

  • How challenge increased inclusive fitness in carriers of allele/trait

  • How did those with trait produce more offspring with trait than those without the trait

Example: Cognition

  • "What environmental challenge caused ancestors to gain a fitness advantage from the cognitive adaption?"

    • The challenge may not have related to the function of cognition at the time

    • Are the challenges which cognition helps with today the same as the ones which led to its evolution, or does intelligence have new functions?

2. Form of evolved trait

  • Specific abilities for one use?

  • Multiple uses?

  • If intelligence is modular its function may have been the same

3. Chronology of trait

a) Sociocultural variation

  • Modern: cross-cultural variation

  • Evolutionary variety between cultures

  • Understand modern human psychology - individual and social environments

  • Recent evolution of trait

b) Evolution since divergence

  • Ancient: Evolutionary changes since divergence from last ancestor

  • Change in biological potential seen via archaeology, knowledge modern humans and last common ancestor

  • Behaviour leaves little material trace so archaeology rooted in past environment is more accurate

c) Evolution before divergence

  • Adaptions in our last ancestor with the potential for intelligence

  • Roots of intelligence have own evolutionary origins (challenges in past)

  • Presence and cause of intellect of the common ancestor can only seen via comparative study


As humans and chimpanzees/bonobos are more closely related to each other than any of them are to gorillas and orangutans, our last common ancestor is only 4.5m years old. This is too short a time span for any intellectual development. We need to look at its roots before our divergence. Modern comparative studies of animals shows wide intellectual differences, this provides evidence of the stages of intellectual development in human past.

Evolutionary Reconstruction

Evolutionary reconstruction uses comparative evidence to reconstruct the human past
  • The distribution of the characteristic in the living members is used to reconstruct its origin in the past

  • We can reconstruct the earliest phases of human behavioural evolution without fossil evidence

  • Similar to a family tree we use the phylogeny of primate relatives

    • Each biological branch on this family tree is a common ancestor

  • Existence of ancestors reliable from modern studies

  • Fossils/bones hard to attribute as lineage may have died out quickly

  • Phylogeny based on molecular and DNA similarities

  • Change occurs at constant rate overtime

  • So we can roughly calculate dates of ancestor

Traits shared with certain animals show its evolutionary origins:

  1. All monkeys = early evolutionary origin (approx. 25-30m ya)

  2. Great apes = trait evolves12-25m years ago

  3. Chimpanzees = trait evolves 4.5-6m years ago

  4. No species share trait = trait evolves after 4.5m years

  • Where trait is developed by convergent evolution (independently in different species) this cannot tell us how it evolved in humans but perhaps its function

  • Primate comparison allows time-frame for human behaviour

Complex Primate Behaviour

Social Support:

  • Monkeys and apes interact in third parties

  • Rely more on alliances to give power in competition

  • Alliances form among kin and non-kin


  • Important trade in alliances

  • Repaid by support in fights/tolerance at feeding site

Socially complex:

  • When major alliance threatened by minor argument, even opponents will reconcile

  • Obligation and influence of relationships key

Analysis of Social Rankings:

  • Socially knowledgable

  • Monkeys attacked by dominant animals react to assert their power

  • Attacked monkeys redirect aggression to weaker parties (like bullying)

  • Attack young relatives/subordinate females to gain power

  • Choice of victim shows awareness of social rank, opponents, dominant members and alliances

  • Calls and responses to monkeys shows they are aware of:

  1. Other kinships

  2. Dominance and social rank of other members

  3. Membership of groups they were never part of

Deception and Dominance:

  • Monkeys and apes use social knowledge for manipulative tactics (deception to get what they want)


  • Dominant male stops female gorillas from mating with subordinates

  • So she 'gets left' to be out of site to copulate

  • Invite subordinates and copulate quietly

Whiten and Byrne Survey of Deception:

  • Primatologists rarely publish 'anecdotes' of deception

  • Survey done to see cases of deception

  • Results suggest tactics varied but deception is used by primates


  • Young baboon screamed as if hurt when saw adult with food

  • Mother scare off 'aggressor'

  • Young gets food

  • AND Young aware of:

  1. Ensuring this is when mother out of sight

  2. Mother's rank is higher than adult

  3. Not reusing tactic often on same person

Why do primates have social complexity?

  • Quick at remembering socially relevant info

  • It is a species typical principle based on genetics

Trial and Error learning:

Because primates have fast social learning and connect social facts to environmental circumstances, they can quickly learn from situations


1. Event happens (Baboon attacked by adult)

2. Events follow (Mother protects young and gets food)

3. Application (Use situation is deceptive way next time)


Learn based off observing others

Ability to Learn:

  • Based off size of neocortex

  • Ratio neocortex linked to larger brains

  • Dunbar: ratio also linked to size of group/social complexity

  • Size neocortex may also be related to recognition (social or environmental - such as fruits)

  • Apes have brain x2 size of mammal of same body mass

Feedback Loop:

  • Increasing social complexity may select for brain size

  • Increasing brain size affects behavioural complexity

  • (neocortex ratio affect frequency of deception)


  • Larger brains evolved in response to a need for social skills, this increased brain size allowed for rapid learning which underlies the social sophistication of apes

Inability to understand mental state:

  • Tempting to assume animals using deception understand the situation

  • BUT comprehension of deceit and situation is not necessary

  • Rapid learning based off observation and application rather than understanding

Dorothy Cheney and Robert Seyfarth Experiment

  • Mother approached by "predator" when infant

  1. a) can see threat

  2. b) cannot see threat

  • In both circumstance mother alerted child of threat

  • Unaware of infants mental state of seeing or not

  • This explains why animals who are manipulated by deception do not understand what is happening

  • BUT Chimpanzees and apes show knowledge of intention:

Sarah Boysen Experiment

  • Chimpanzee approached by "predator" when friend

  1. a) can see threat

  2. b) cannot see threat

  • When chimpanzee realises its friend cannot see a call is raised and it acts to "protect"

  • When chimpanzee realises its friend can see there is no call raised

  • Chimpanzees can distinguish mental states

  • In the wild only chimpanzees teach offspring in a way that is aware of infants ignorance

Ability to understand mental state is unique to Great Apes:

  • Chimpanzees aware of when being deceived e.g. annoyed at a "look behind you" trick when there is nothing there

  • Cercopithecine monkeys use deceptive tactics more frequently than great apes

  • BUT the ways the apes use tactics imply awareness of what they were doing

  • Chimpanzees must have intentional social manoeuvring (e.g. switch allegiances)


  • Frans De Waal observe in Chimpanzee Politics:

  • Male who did not have qualities to become top ranked himself

  • Male used clever switches of allegiance to gain more effective power than held by either of the two males he supported

  • Once they began to solidify position with his support he defected to the other

Reasons behind social manoeuvring:

  1. Males who require powerful ally to hold top rank were always vulnerable

  2. A male who gradually built up a broad base of support among weaker males and females males was able to hold tenure far longer


  • Gordon Gallup notice chimpanzees, but not monkeys, show self-recognition

  • E.g. Looking in the mirror to examine hidden areas of their bodies such as teeth and gums, or making repeated, exaggerated gestures while watching their reflections

Complex understanding:

  • Few Old World monkeys regularly make/use tools

  • Chimpanzees in West Africa use two rocks as hammer and anvil to break nuts

  • Chimpanzees in East Africa use tools and bimanual coordination to capture ants

Manipulation of tools and techniques:

  • Capuchins use tools but in simplified situation - obvious visibility of hole of an open termite mound

  • Chimpanzees can termite fish with less clear mound, without a hole, and delicately guide tool - more abilities beyond use of tools


Chimpanzees can plan their tactics driven by knowledge not immediate stimuli and show awareness of possible outcomes


  • No suitable plant for fishing grows near termite mound, chimpanzees plan to make tools in advance to bring to site

  • No suitable rocks near nuts, chimpanzees carry a hammer-stone before they get to tree

Cultural Variation:

  • McGrew shows local traditions in chimpanzee tool use as in human cultures:

  1. Some discard frayed tools

  2. Some rotate tools to use less worn end

  3. Some 'resharpen' tool

  • The use of inefficient methods shows social learning by imitation

  • Trial-and-error requires progression towards optimal technique and cannot pin point inefficiency if there is no more efficient method attempted to compare to

Elaborate series of actions:

  • Tool manipulation and planning is a great ape trait


  • Gorilla diet is mainly of plants which use stings/hard castings/mechanics which make it hard to it

  • Gorillas use techniques to minimise stings from nettles

  • Remove leaf blades in gathered bunch by using half-open hand to strip stem

  • Remove stems/petioles with worst stings

  • Folds leaf bundle so only one leaf sting side is exposed

Why are great apes cognitively superior?

  • Efficient Skill Learning Mechanism: Imitation

  1. Gorilla: population consistent techniques and individual variation at detail

  2. Chimps: inter-population tool use differences not explained by ecology

  3. Orangutan: copy human traditions (e.g. building fire)

  • Comprehend objects and events - mental states and tool behaviour

  • Monkeys cannot acquire complex novel behaviour by observation and imitation

  • Great ape ancestor had cognitive potential to plan, imitate and understand others

    • Not due to further neocortex size (neocortex affects learning speed) so something else affect ape mental complexity (maybe structure?)

Selection Pressure:

  1. Complex Social interaction

  • 30m years ago: monkey and ape ancestor develop rapid learning and larger brain

  • Due to: Need for larger permanent groupings

  1. Monkey vs Ape Competition

  • 12m years ago: apes and human ancestor develop ability to take account of others' behaviour and understanding

  • Due to: Large size of apes adapted to brachiation (for trees) mean walk in awkward gait on knuckles

  • Old World monkeys have adv of eating unripe fruit

  • SO apes develop cognitive abilities such as foraging and planning to survive intense competition with monkeys

What cognitive skills were we left with?

  1. A causal understanding of complex behaviour, enabling novel schedules of actions to be put together and allowing the behaviour of others to be used as a source of ideas for new action schedules; in other words, nonverbal planning and skill learning by imitation

  2. A degree of understanding of the intentions of others-what they want, know, and think; in other words, possession of a theory of mind

Evolution of language would be impossible in a species in which individuals could not imagine that other individuals know things that they do not know themselves.
  • Language is acquired by imitation - not by direct copying

  • Children do not parrot our parents' words

  • Child "imitates" a word, the actual sounds are quite different and the use of the word is individual

  • An understanding of a novel behaviour is gained so an individual can express it in their way


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