Primate Morphological Traits

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Primate Morphological Traits

• Allometry of Brain and Body Size

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Us and Them

• No single trait differentiates primates from
  other animals

3
2 Features that Stand Out

• Larger brains, with variation within
• Greater dexterity and mobility than other
  animals, with variation within

4
Brains

• Neocortex is larger
• Cognitive abilities
• Reasoning
• Consciousness
• 50-80 of total brain volume

Neocortex in blue, from http//www.nibb.ac.jp/bri
sh/Gallery/cortexE.html

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Why develop a bigger brain?

• Typically, morphological traits are a function of
  ecological adaptation, tied to the
  
• Need for food
• Need to mate to reproduce
• Need to diminish predation and other threats

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Social Brain Hypothesis Robin Dunbar, 1988

• Larger brains correlate with more social
  primates
  
• Larger brains larger social groups

Colored areas frontal cortices
http//www.nature.com/neuro/journal/v5/n3/fig_tab/
nn0302-190_F1.html

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Competition or Cooperation

• Allies in social groups ensure access to
  resources and protection
  
• but
• Neocortex size is also correlated with tactical
  deception
  

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Competition or Cooperation

• Tactical deception acts or behaviors that
  deliberately mislead others a form of
  Machiavellian intelligence
  
• Machiavellian or Social Intelligence
  Hypothesis(read particularly the last few
  paragraphs)
  
• Machiavelli defined

Rhesus macaques from http//scienceblogs.com/zoo
illogix/Langurs20Fighting.jpg
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Competition or Cooperation

• Others argue in favor of expedience
• Primates have the ability to adjust competitive
  and cooperative behaviors as needed
  
• Larger neocortex cooperation stimulates reward
  centers located in this part of the brain
  

Bonobos from http//www.primates.com/bonobos/wil
d-bonobos.jpg

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Memory

• A larger neocortex has ecological advantages
• Memory remembering where food is located, how
  to extract food

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Allometry

• 2 traits can be related in 2 ways
• Isometrically 2 variables increase or decrease
  in direct proportion to one another
  
• Allometrically 2 variables increase or decrease
  at different rates rates
  
• e.g., hominid brain size relative to body size
  beginning around 2-3 mya
  

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Body Allometry Diet

• Basal Metabolic Rate BMR
• Rate at which energy is used to maintain bodily
  functions at rest
  

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Allometry Body and Brain

• BMR (and brain size) allometrically related to
  body weight
  
• Greater weight lower metabolism eating more
  lower energy foods (e.g., gorillas are folivores,
  top photo)
  
• Lesser weight higher metabolism eating more
  high energy foods (e.g., chimps favor fruit
  (bottom photo), nuts)
  

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Allometry Body and Brain

• Gorillas larger bodied, smaller brain
• Chimpanzees smaller bodied, larger brain
• Brains require high amounts of energy to run
• 2 of body weight
• 20 of energy to run

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Why bigger or smaller brains?

• Metabolic rates might constrain brain size
• Or
• Skills needed to find high energy foods might
  result in selection for bigger brains

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Jarman/Bell Principle

• Originally explained antelope behavior, but
  applies to primates
  
• Relationship between body size, metabolic rate,
  and food quality
  

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Life Histories

• Larger brains relate to extended life histories
• Social consequences?
• Long infant dependency allows for more time to
  develop socially
  

Far right collared lemurs Near right macaques
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Life Histories

• Presocial animals well-developed at birth
• Altricial animals under-developed at birth
  long dependency (see Table 2.1 page 43)
  

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Jarman/Bell Principle and Sexual Dimorphism

• Body size and physical differences between the
  sexes
  
• Within the same species, when compared to
  females, larger males
  
• Require more time to develop
• Have a greater dietary intake
• Spend different amounts of time eating
• May eat different types of foods

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The End

• Next topic More primate morphological traits