Brain

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Brain BehaviorPsych 545
Dr David A Kaiser Office Bldg 6 A116 x6773
dakaiser_at_mail.rit.edu www.rit.edu/dakgsh
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Largest Brain on planet, 9.2 kg
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Belongs to Sperm Whale
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Absolute Brain Weight Does it reflect
intelligence?
Species Adult Brain Weight (grams)
Chimpanzee 450
Human 1,350
Bottlenosed dolphin 1,600
African elephant 6,075
Fin whale 7,200
Sperm Whale 9,200
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Relative Brain Weight
Species Brain to Body Weight
Human 2.1
Bottlenosed dolphin 1.2
Chimpanzee .7
African elephant .5
Killer whale .1
Cow .08
Sperm Whale .02
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Encephalization

• Increase in brain size during evolution of
  SPECIES, with no concomitant increase in body
  size
• Of all animals, man has the largest brain in
  proportion to his size - Aristotle

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Encephalization
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Encephalization Quotient (EQ)

• Anatomical estimate of species intelligence
  (non-behavioral)
• EQ ratio of brain weight of animal to brain
  weight of typical animal of same body weight
  (Jerison, 1973)
• EQ represents index of residual value of brain
  mass
• Total Brain Mass Brain for body size
• Residual
  brain for higher functions

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Encephalization Quotient (EQ)

???????? 9.0
Human 7.4
Dolphin 5.6
Killer whale 2.9
Chimpanzee 2.5
Rhesus Monkey 2.1
Elephant 1.9
Whale 1.8
Dog 1.2
Cat 1.0
Horse 0.9
Sheep 0.8
Mouse 0.5
Rabbit 0.4

• Human neocortex is 3.2x larger in volume than
  nonhuman primate with our body size (Jerison,
  1973).
•     
•     
•  
• Overview Quiz
• TLE

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Encephalization Quotient (EQ)

Hummingbird 9.0
Human 7.4
Dolphin 5.6
Killer whale 2.9
Chimpanzee 2.5
Rhesus Monkey 2.1
Elephant 1.9
Whale 1.8
Dog 1.2
Cat 1.0
Horse 0.9
Sheep 0.8
Mouse 0.5
Rabbit 0.4
          1 g brain for hummingbird

• Human neocortex is 3.2x larger in volume than
  nonhuman primate with our body size (Jerison,
  1973).
•     
•     
•  
• Overview Quiz
• TLE

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EQ through evolutionary time

• Are we evolving into smarter and smarter
  creatures? Or was humanity a fluke?
• In other words, was there a neural arms race in
  the past or an unusual mutation process in one
  line of primates?

• Human neocortex is 3.2x larger in volume than
  nonhuman primate with our body size (Jerison,
  1973).
•     
•     
•  
• Overview Quiz
• TLE

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Evolution of behavioral complexity

• Neural arms race in mammalian group only

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• In all mammalian orders including primates

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Neurobehavioral Arms race
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Monkeys, Great Apes, and Us
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Four leaps in braininess

1. To Primate
2. To Australopithecus
3. To Hominid
4. To Homo sapiens

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Brainy Newcomers
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Convolution Index wrinkliness

• BUT Cortex width human 2.9 mm, dolphin 1.7 mm
  and conversative (not progressive) organization

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Our Family
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...And Then There Was One

• Sixteen Species of Extinct Humans
• Ardipithecus ramidusAustralopithecus
  anamensisAustralopithecus afarensisAustralopithe
  cus bahrelghazaliAustralopithecus
  aethiopicusParanthropus boiseiParanthropus
  robustusAustralopithecus africanusAustralopithec
  us garhiHomo rudolfensisHomo habilisHomo
  ergasterHomo erectusHomo antecessorHomo
  heidelbegensisHomo neanderthalensis
• Homo sapiens

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We shared planet with two other human species as
recently as 25,000 years ago Homo erectus and
Neanderthals

• Coincided with unstable weather (4 ice ages)

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Can human brain get any bigger?
Hominid Million yrs Weight (g)
Australopithecus 5.0 500
H habilis 2.5 725
H erectus 1.7 1000
H heidelbergensis 0.6 1200
H neanderthalensis 0.2 1500
H sapiens 0.2 1350
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Encephalization abuse within species
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General Features of Brain Evolution

• Relative increase in brain size
• Relative increase in telencephalon (cortex) over
  midbrain and hindbrain
• Relative increase in representation of sensory
  information over motor responses
• Relative increase in cortex involved in
  associative integration than (primary) reception
• Greater differentiation of neocortex, with more
  cell diversity
• Relative importance of biophysical senses over
  chemical senses in more sentient species
• Convergent evolution in all mammalian groups of
  these morphophysiological features

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Neoteny Childlike features into adulthood
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Bonobo and Common Chimp
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What did big brain gives us? Social or Cognitive
Intelligence?

• Example of cognitive Tool Use in Animals ,
  termite fishing by bonobo

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Social Intelligence

• The Machiavellian Hypothesis Richard Alexander
  (1970s) suggested that main evolutionary pressure
  behind human intelligence was competition with
  other people, notably sexual competition between
  individuals of the same sex.

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Dunbar (1992)- natural group size
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Hominid social evolution