AS

Chapter 8: Primate Life Histories and the Evolution of Intelligence 

Behavioral and Life History Traits Common in Primates:

  • Large brains
  • Long juvenile periods
  • Learned behaviors
  • Behavioral flexibility
  • Long lives
  • Longevity via selection on brain
  • Brain size correlates well with life span across primate species
  • Evolutionary trade-offs: large brains energetically costly to maintain. Requires high calorie intake. → Advantages of having a large brain must have exceeded costs.
    • Social intelligence hypothesis: the theory that primates having large brains evolved to help them navigate complex social systems in primate groups (ex. keep track of alliances)
    • Not highly supported because if the social intelligence hypothesis were true, we would expect intelligence to be strongly associated to group size. But social complexity is evidently much greater in humans than our ape ancestors.
    • Extractive foraging hypothesis: primates evolved large brains because larger brains provide the ingenuity required to get hard to reach food sources (ex. tool use to extract nuts)
    • Behavioral flexibility hypothesis: primates evolved large brain because it let them learn new solutions to problems and cope with both ecological and social challenges, as larger brains provide the ingenuity required to come up with complex solutions.
  • Encephalization: ratio of brain mass to body mass increases with primates.
  • Our brains account for 20% of our metabolic energy
  • Our brains account for 2% of our total body weight.
  • Slow maturation and late reproduction:
    • growth enhances reproductive success
    • fewer offspring are produced overall
    • energy is converted from current reproduction to maintenance

  • Compared to most other animals, primates rely more heavily on learning to survive and reproduce successfully.

  • Senescence: The condition or process of deterioration with age. The deterioration of an organism's physical abilities, which occurs as they get older.

  • ==Primate coalition formation:== at least 3 people are required to form a coalition, and several different kinds of interactions are going on simultaneously. These interactions normally include:

    • an aggressor attacking a victim
    • the victim soliciting support from an ally
    • and the ally intervening on behalf of the victim against the aggressor

  • Primates who participate in coalitions have knowledge of third-party relationships.
    Knowledge of third-party relationships enables individuals to predict how others will behave and gives animals a good idea of who will (successfully) support them and who will intervene against them in future confrontations with known opponents.

  • ==Redirected aggression:== Exhibited when a primate is attacked and then immediately threatens or attacks a lower-ranking group member who was not involved in the original incident.

  • ==Theory of mind:== refers to the idea that a primates' ability to predict what others will do in particular situations is based on their knowledge of the mental states of others

  • Primates with relatively large executive brains are more likely to innovate, learn from others, and use tools than primates with relatively small executive brains.

  • Selective pressures are much weaker on traits that affect only the old because:

    • Selection only acts very strongly on traits that affect infants and juveniles because if they do not survive this period, they cannot pass their traits on to any descendants.
    • In contrast, selection acts less strongly on traits that affect animals late in their lives because they will have already produced offspring before the effects are felt.

  • Experiments conducted by Cheney and Seyfarth:

    • playback experiment where female vervet monkeys heard a tape-recorded scream of a juvenile vervet monkey. When the call was played, the mother of the juvenile stared in the direction of the speaker. This behavior suggests that mothers recognized the call of their own offspring. However, the other females that could hear the scream, they looked directly at the juvenile's mother.
    • conducted an experiment where female baboons listened to a recording of one female's grunt followed by another female's submissive fear barks, they found that female baboons responded more strongly when they heard a ==higher-ranking female responding submissively to a lower-ranking female's grunt.==

Ecology and Life History Variables of Orangutans:

  • Fruit is less seasonal in Sumatran forests than it is in Bornean forests
  • Sumatran forests have more fruit than Bornean forests
  • Bornean orangutans have shorter interbirth intervals than Sumatran orangutans
  • soil quality is higher in Sumatra than it is in Borneo.

%%This is why orangutans in Sumatra have a larger brain than those in Borneo.%%

Large Primate Brain: Brain Structure:

  • Hindbrain
  • Cerebellum: coordinates muscular function
  • Brain stem: very ancient structure that regulates bodily functions like cardiac, respiratory and sleep cycle.
  • Phylogenetic history: often referred to as reptilian brain.
  • Midbrain Forebrain or Cerebrum
  • 4 lobes (occipital, frontal, temporal, parietal)
  • Neocortex: is associated with problem solving and behavioral flexibility and regulation, which is critical in primates.
    • primates are knowledgeable about social relationships within their groups, animals living in large groups have larger neocortex ratios than animals living in smaller groups
    • To test hypotheses about cognitive ability, researchers focus on the development of the neocortex, the part of the brain where the most substantial evolutionary changes in size and complexity have taken place.