How diet affects the brain: evolution

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How diet affects the brain evolution
development

• Greg Downey
• Lecture 5.2

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Encephalization Bigger is better or something
more?
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Relative brain sizes
Most formulae based on body size suggest human
should be 600 cc.
Source James K. Rilling. 2006. Human and
NonHuman Primate Brains Are They Allometrically
Scaled Versions of the Same Design? Evolutionary
Anthropology 15 65-77.
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Encephalization expected brain size
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How big is the human brain?
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Encephalization Evolutionary trends
Graphic from Getty Images
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Encephalization among hominins
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Brain growth over evolution
Hominin doesnt just get bigger, it spikes upward.
Relative brain size
Time, in millions of years ago
http//www.talkorigins.org/faqs/homs/a_brains.html
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How big does a brain have to be? 750cc - Author
Keith.
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The first of our genus Early Homo
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Homo habilis (Australopithecus habilis?)

• Habilis because of handy man (discovered
  1960).
• Remains 2.3-1.6 mya.Overlaps Australopithecenes
  Paranthropus.
• Ape-like body.
• Skeletal traits variable.H. rudolfensis for
  robust variant.
• 600-700 cc. brain.Is the big jump with H./A.
  habilis or with H. erectus?
• May have made stone tools.

Homo habilis (skull OH 24) Source
http//www.mnh.si.edu/anthro/humanorigins/ha/a_tre
e.html
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Homo ergaster

• Work man (1976).
• 1.8 mya to .6 mya.
• Larger body than earlier hominins with modern
  proportions (savanna populations).
• Human-like traitsLeft Africa for Eurasia
  (range).Diet included meat (cooking?).Tool
  use.Brain size around 800 cc.
• Used to be called H. erectus, but now name is
  reserved for East Asian remains.

Nariokotome Boy KNM-WT 15000 Remains found at
Lake Turkana Photo by Kenneth Garrett/National
Geographic
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Comparative neurology

• Human brain not simply quantitatively different
  (bigger).
• Qualitative differences are crucial.
• Terrence Deacon searching for special language
  part of human brain.

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Relative brain sizes

• Cerebral cortex much larger.

Rats cortex postage stamp
Monkeys post card
Humans four pages
Chimpanzees page of printer paper
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Relative brain size
or... the neocortex is about the size of two
large pizzas.
Thanks to Paul Mason for this slide!
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Neocortex shape (sulchi, fissures, gyri)
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Primordial plexiform layer (first oldest)
becomes I subplate (SP) in human. Cortical
plate divides PPL forms II-VI.
http//www.nature.com/nature/journal/v437/n7055/fi
g_tab/nature04103_F1.html see also
www.brainmuseum.org
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Brain areas that grew

• Frontal lobe, associated with synthesizing
  information from other areas and inhibiting
  action.
• Volume of white matter, brain interconnections,
  grows faster than neocortex, eventually
  constituting 34 of human brain.
• Differentiation of tissue (but only through
  development).

Graphic from Getty Images
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Social brain hypothesis

• Average group size correlates with the ration of
  neocortex to the rest of the brain.

R. I. M. Dunbar, et al. 2007. Evolution in the
Social Brain. Science 317, 1344-1347. DOI
10.1126/science.1145463
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Social brain hypothesisProblem What kicks off
the process?Larger brain only adaptive once
social life complex.
Possibility dietary change?
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Is intelligence all in the brain?

• Human intellectual abilities, however, are not
  carried entirely by genes.
• Feral children, for example
• Human company influences intellect.
• Other primates raised in human environments
  develop greater intelligence.
• E.g. tool use in encultured chimps
  orangutans.
• Carel van Schaik gregarious adult social life
  key.
• Human is especially immature at birth.
• Brain less developed at same age to open wider
  learning window.

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Extended brain

• Wont deal with it today (during week on
  Language)...
• Language, culture, symbolic systems and other
  devices both create external supports for
  cognitive abilities, and...
• Generate developmental environments that shape
  the biological unfolding of humans.
• Human brains are shot through with culture.

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Diet and brainWhat were we meant to eat?

• Hominin dietary patterns

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Meat and Livestock Australia ad campaign Red
Meat. We were meant to eat it. Downloaded from
www.mla.com.au (Go to website for functioning
video link.)
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Problems with a big brain

• Why doesnt every animal want one?

Graphic from Getty Images
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Expensive tissue hypothesis

• Large brain is energy hungry human brain
  consumes 25 of our energy when resting.(See
  readings!)
• Brain tissue expends 9x body tissue average.
• In infants, 75 of bodys energy!Only human
  babies fat (15).
• Need for energy-rich food.

Graphic from Getty Images
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Human diet

• Richard Wrangham argued that human could not eat
  enough food on chimp diet to survive.(Besides,
  he found the fruit very unpleasant.)
• H. ergaster brain size increasing while teeth are
  growing smaller.Would need more than 5 kilos/day
  in raw plant food.Around 6 hours/day chewing.
• Wrangham argues that cooking would be necessary.

Graphic from Getty Images
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Cost of bigger brain

• Examining energy demanding organs.
• Human gut, especially, is significantly smaller
  than predicted by patterns in other species.
• Makes digestive tract less efficient.

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Comparative GI tract

• Humans have comparatively long intestine
  shortened colon.
• Resembles other primates (such as capuchin
  monkeys) who process food in hands.

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Diet, selection and reduced pressure
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Frugivore gut

• In spite of these challenges, humans clearly have
  frugivore-derived gut (vegetarian).
• Pouch in colon to ferment plant foods.
• Intestine is expandable and quite long (compared
  to carnivore) stomach small.
• Gut transit time in humans 38-48
  hours.Carnivores 2.5 to 26 hours.

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The Radiator Hypothesis

• In hot environment, brain temperature may be the
  one biggest limit on survival (and human brains
  generate energy).
• A. afarensis began to develop openings in the
  skull (emissary foramina) through which blood
  could flow out to cool the brain.
• Brain temperature was constraint radiator
  released this constraint.

Lower photo from Wolfgang Zenker and Stefan Kubik
(19964) illustrations from http//www.anthro.fsu
.edu/research/falk/concepts.html Images and
discussion from Dean Falk, http//www.albany.edu/b
raindance/Theories.htm.
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The Radiator Hypothesis
Cranial capacity
Mastoid foramina
Parietal foramina
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How to afford your brain

• Evolutionary strategies

Graphic from Getty Images
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Man the hunter hypothesis

• Did hunting drive human evolution by fueling
  hungry brain?
• Evidence of butchering in stone marks on bones
  refuse piles.
• Evidence from parasites.
• Modern foragers get 50 of calories from meat
  (chimps lt3, who dont host tapeworms).

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Man the hunter hypothesis

• Might seek especially rich foods (like brains or
  marrow).
• Would also help explain expanding range of H.
  ergaster (out of Africa).
• But data and jaw suggests small animal hunting
  (not romantic image of big game hunting).

Graphic from Getty Images
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Something fishy about the brain?

• Shoreline foraging provided high protein frogs,
  clams, fish, bird eggs (fish bones with H.
  habilis).
• Shore rather than savannah as the crucial niche.
• Evidence Iodine deficiency.
• Possible, but still theoretical

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H. sapiens and P. boisei teeth
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Recent changes in the brain
Graphic from Getty Images

• In last 35,000 years, brain size has shrunk 11.
• In last 10,000 years, brain size has shrunk 8.
• Are domesticated food sources adequate?

Ruff, Trinkaus Holliday 1997.
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Diet of early Homo?

• Evidence suggests no single pattern
  (unspecialized frugivore) tooth-wear patterns,
  for example, vary.
• Perhaps the best evidence of dietary versatility
  and ability to inhabit variety of ecological
  niches (like the versatile lower body for
  locomotion).
• The most interesting thing is the ability to meet
  energy demands from varied niches with
  underdeveloped guts (debated), jaws and teeth.
• Humans likely omnivores for a very long time
  clearly occupied a different niche from other
  living Great Apes (see also evidence from
  tapeworms).
• Modern health problems are not because we are
  eating the wrong food the problem is the lack of
  activity and surplus of calories.

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Sex and reproduction

• Week Six

Graphic from Getty Images
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Select References (see unit outline for more)

• Aiello, L. C., and P. Wheeler. 1995. The
  expensive-tissue hypothesis The brain and the
  digestive system in humans and primate evolution.
  Current Anthropology 36199-221.
• Bradbury, Jane. 2005. Molecular Insights into
  Human Brain Evolution. PLoS Biology Biology
  3(3) e50. DOI 10.1371/journal.pbio.0030050
• Dunbar, R. I. M., et al. 2007. Evolution in the
  Social Brain. Science 317, 1344-1347. DOI
  10.1126/science.1145463
• Hladik, C. M., D. J. Chivers, and P. Pasquet (et
  al.). 1999. On Diet and Gut Size in Non-Human
  Primates and Humans Is There a Relationship to
  Brain Size? (and commentary) Current
  Anthropology 40(5) 695-698. (pdf available)
• Hladik, C. M., and P. Pasquet. 2002. The human
  adaptations to meat eating a reappraisal. Human
  Evolution 17(3-4)199-206. (pdf available)
• Rilling, James K. 2006. Human and NonHuman
  Primate Brains Are They Allometrically Scaled
  Versions of the Same Design? Evolutionary
  Anthropology 15 65-77. (pdf available)
• Ruff, Christopher B., Erik Trinkaus and Trenton
  W. Holliday. 1997. Body mass and
  encephalization in Pleistocene Homo. Nature 387
  173-176.
• Ungar, Peter S., Frederick E. Grine, and Mark F.
  Teaford. 2006. Diet in Early Homo A Review of
  the Evidence and a New Model of Adaptive
  Versatility. Annual Review of Anthropology
  35209-228.
• Wrangham, R. W., J. H. Jones, G. Laden, D.
  Pilbeam and N. L. Conklin-Brittain. 1999. The
  raw and the stolen Cooking and the Ecology of
  Human Origins. Current Anthropology 40567-594.
• Diet diagrams from Aiello and Wheeler. 1995.
  Current Anthropology. Reproduced in
  www.beyondveg.com.