Primates

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Feb 23, 2014 (3 years and 7 months ago)

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The Rise of Homo sapiens

Chapter 5


Ashley White


Human brains = Primate brains


Much of our brain’s anatomy and the way we
think is the way it is because we are primates


Primates are the Order within the Class
Mammalia


Encompasses monkeys, apes (including humans),
and prosimians


All living primates share a common ancestor


Mammal who lived 50 million years ago, during the
great expansion and diversification of mammals that
followed the extinction of the dinosaurs


Most living primates are tropical


2 major exceptions are humans and macaques
(Japanese snow monkeys)



Most primates are arboreal


Spend some or all of their lives in trees


This is reflected in primate anatomy, including the
anatomy of those who no longer live in trees


Grasping hands and feet for locomotion


Well
-
developed visual system


Because primates have been around for over 50
million years, they have had ample
opportunity to evolve a wide variety of specific
anatomies and adaptive niches



We will review the developments, old and
recent, that are directly relevant to the
evolution of human cognition


Primate brains are adapted to the demands of
an arboreal way of life


Expanded ventral premotor cortex, part of the motor
cortex controlling hand and finger movement


Good at directing fine motor action



The most salient developments occurred in the
areas of the brain that process visual
information


The center of a primate’s retina is densely
packed with photo
-
receptors


This allows for detailed perception in the center of the
visual field


Perceptual information passes from the retina
though the lateral geniculate nucleus of the
thalamus to the primary visual cortex of the
occipital lobes


Here, the “raw” data is initially processed and
passed on to the parietal and temporal lobes,
where more complex analysis occurs


Primates are particularly good at recognizing
shapes and locating themselves in space


Stereoscopic Vision:


Primate eyes face forward, with considerable overlap in
the visual fields of each eye


By comparing the two slightly different images, the
visual cortex is able to construct depth


Advantage: depth is perceived easily when
moving about in the tops of tropical trees


Disadvantage: primates cannot see to rear


Hemifield (half
-
field) vision:


Source of “lateral visual field neglect” in humans


Unlike humans, most mammals have the entire
visual field of each eye processed
contralaterally


If brain damage occurs, the ability to process
information on one side of the visual field may
be lost


No one is quite sure why the primate visual
system works this way


About 40 million years ago, the large group of
primates that includes monkeys, apes, and
humans diverged from the earlier primates


These earlier primates survive today as the prosimians


Anthropoids were larger than the prosimians


Developed a dietary focus on fruit and leaves,
unlike the largely insectivorous prosimians


Also had larger brains, and in particular a
larger neocortex


With the anthropoids, there were new
developments to the visual system


Trichromatic color vision results in the full range
of color perception


enjoyed by humans, apes, and monkeys


Required a mutation (probably a gene duplication)
that added a third variety of cone to the retina,
along with neural resources in the primary and
secondary cortices


It evolved in anthropoid ancestors as an aid to
detecting food in complex forest canopies, most
likely fruit


Over time, anthropoids also developed a
much
-
heightened ability to recognize faces and
facial expressions


This resulted from an expansion of the infero
-
temporal visual cortex, the area of the
neocortex linked to shape recognition


This is sometimes termed the “ventral
pathway” of visual processing


Information passes from the primary visual cortex of
the occipital lobes forward to the temporal lobes, where
more sophisticated visual processing takes place


The neurons involved in facial recognition are
linked to the amygdala, the structure that
attaches emotional value to perceptions


Anthropoids use facial expression to
communicate emotional states, which play an
essential role in anthropoid social behavior


It is social behavior that explains not just the
increase in anthropoid inferior temporal visual
cortex, but also the increase in overall brain
size and neocortex size


Anthropoids have an EQ of about 2.1


Overall brain size is about twice as large as predicted
for a placental mammal of comparable size



However, there is a great deal of variability


Old World monkeys

1.05


Humans

6.0


Some of this variation in brain and neocortex
size appears related to the total amount of
visual information coming in from the eyes


This suggests that visual specializations of various
kinds may effect overall brain size


Some of the variability also appears to result
directly from the evolutionary trade
-
off between
brain size and gut length


Folivory
(leaf
-
eating) anthropoids have smaller
brains and neocortices than
frugivory

(fruit
-
eating)
anthropoids


Leaves must be fermented in a very long gut in order to yield
digestible carbohydrates


This requires a heavy metabolic investment in
digestion


The balance cannot be made up by decreasing reliance on
hearts, kidneys, or livers (other metabolically expensive
tissues)


So…brain size must be limited in folivores

This explains why folivores have smaller brains,
but why do frugivores need larger brains?







There are 2 possibilities:


Something about foraging for fruit
selected for

larger brains and neocortices


Probably “mental mapping”


The ability to locate oneself and others, and navigate in
complex forest habitats


This spatial mapping ability is a function of the
parietal cortex (the dorsal pathway of visual
processing)


In tropical forests, fruit is distributed in small,
concentrated patches that ripen at different times
throughout the year


Because fruit is a high
-
quality nutrition, it is under great
demand


There is serious competition from birds and other mammals


Anthropoids have a mental map of territory


Move efficiently between patches


Remember where patches are and when they are likely to be
available


“Plan” a foraging pattern that is more effective in the face of
competition


The switch to the concentrated, easily
digestible, high
-
quality nutrition of fruit
released selective pressure against

larger brains


Freeing them to expand in response to other selective
pressures


Probably social complexity


Anthropoids live in a variety of social systems,
from the mostly solitary orangutan males to
large multi
-
male/female troops of baboons


One association of complexity is group size,
based on assumption that more individuals
produce more interactions


However, when primatologists tried to correlate brain
size with group size, they found no relationship


But, group size does reliably predict neocortex size


Human neocortex falls about where it should
for a group size of about 150


Brain size correlates with several life
-
history
factors


Age at first reproduction


Length of the juvenile period



Several ways to explain this:

1) Both brain size and maturation reflect an
increase in body size


But, when body size is controlled, the correlation
remains

2) Natural selection may have favored delay of
reproductive age because of niche complexity
and energetic cost of reproduction, and brain
growth was a by
-
product


But, most brain growth occurs pre
-

and neo
-
natally, so
a simple by
-
product explanation seems weak

3) Selection for brain growth would require
lengthening of juvenile periods and age of first
reproduction, because there is a greater amount
of information to be learned


4) Combination of these and other factors


What is clear: brain growth cannot have
occurred simply through selection for more
neurons in an adult individual


The process entailed changes in brain and
physical development



It was not simple, and it was


energetically expensive


With the exception of humans, apes today are
much less numerous and successful than the
monkeys


There are only four species of great apes (chimpanzees,
bonobos, gorillas, orangutans) , all of which are
declining in number


They were most varied and successful during
the Miocene age (23 million to 5 million years
ago)


It is the slowness of reproduction that placed
apes at a disadvantage, compared to Old
World monkeys


Apes: long gestation, increased inter
-
birth interval, long
juvenile period


Monkeys: reproduce much faster, almost as clever



What we know:


Long juvenile periods and late age of first reproduction
correlate strongly with brain size



What we DON’T know:


Which came first?


Do apes have large brains because they have extended
developmental periods, or did their large brains require
extended development for learning?




Unexpected conclusion:


We can suspect that large brains may be partially to
blame for the apes’ recent evolutionary decline



If large brains no longer yield a competitive
edge, their owners will go extinct.


Large brains are metabolically expensive


Large brains have profound life
-
history consequences




What edge did ape brains initially possess?


Expansion of planum temporale (area on the dorsal
surface of the superior temporal lobe)


Expansion of Brodman’s area 44 (left ventral motor
cortex)



These areas have been linked to apes’ more complex
vocalizations




What edge did ape brains initially possess?


Lateral cerebellum of apes is 2.5x larger than monkeys



This controls many basic postural functions


Also involved in cognitive planning of complex motor
actions, sequential patterning, and procedural learning





Some have suggested that great ape
encephalization is linked to suspensory
locomotion in forest canopies






Others propose that it may be linked to
“complex foraging” and access to embedded
foods




Well
-
known as tool
-
users and tool
-
makers



Habitually use tools to access hard
-
to
-
acquire
foods such as termites, hard
-
shelled nuts, and
honey from well
-
defended nests



Solutions vary between communities, but all
rely on complex motor manipulations of
objects, sometimes requiring a series of tools





Have been observed using tools to break open
nests



“Extractive foraging”


the use of tools to
access hidden and embedded foods


Early Hominins


Probably inherited from the common ancestor




They rarely use tools, but do use organized,
complex manipulations to gain access to the
pith of nettles



Such manipulations require cognitive resources
similar to those required for chimpanzee tool
use



It seems that this pattern of complex feeding is
shared by all of the great apes



This may explain the very significant difference
in the size of the lateral cerebellum, when
compared to monkeys


The specific adaptations we have discussed do
not seem general enough to explain the
increase in overall neocortex size of all
anthropoids


Also doesn’t explain the flexible problem solving
abilities we associate with apes



This generalizability problem led
primatologists to search for features of
anthropoid lives that might have selected for a
general problem
-
solving ability


Social behavior


Nicholas Humphrey (1976)


Suggested that the complex social lives of anthropoids
selected for their problem
-
solving abilities



Richard Byrne & Andrew Whiten (1988)


Pulled together various authors into a volume that
summarized evidence for the leading role of social
behavior in primate cognition


Machiavellian Intelligence


Argues that the most complex part of a
primate’s daily life is the ever
-
changing nature
of polyadic social interactions


Polyadic


more than two individuals


Dyadic


how one relates to one other individual



Primate social groups often consist of adult
females, their offspring, and adult males


Success in reproduction and access to high
-
quality foods requires constant monitoring of
one’s social standing


The most successful individuals monitor not
only dyadic relationships, but also polyadic
relationships


Soap opera = good anthropoid primates


What we know:


There is a correlation between anthropoid neocortex
size and social group size, which probably reflects the
increasing complexity of polyadic interactions in larger
social groups



What we DON’T know:


What is so mentally challenging about polyadic
interactions?


Tactical deception


Theory of mind



Occurs when one individual misleads a second
individual in order to obtain some immediate
goal, normally available to or under control of
the second


Novel response to a
specific

condition



Tomasello & Call (1997)


A female baboon, wanting to groom with a
subdominant male, slowly inched toward a boulder
while in plain view of the alpha male (who would not
approve).


When she reached a position from which the alpha
male could only see her head, she successfully groomed
with the subdominant male.


This is
tactical

deception because the behavior
was tailored to the immediate circumstances


Many organisms use deception, but not
tactical

(camouflage, or feigned injury by mother birds)



Tactical responses are impressive solutions to
problem
-
solving


We cannot over
-
interpret them



Almost all examples of tactical deception
among anthropoids can be explained by
learning



Humans, however, regularly rely on another
ability…



Knowing that other individuals have minds and
beliefs, and these beliefs may differ from one’s
own beliefs


“mind reading”


Usually evaluated through the “false belief test”


A child is shown a situation in which a doll watches the
experimenter place a piece of candy in one of two opaque
boxes. The doll is then removed and placed somewhere out
of view of the table. The experimenter then moves the candy
into the second box (the child is watching all of this). The doll
is brought back, and the child is asked where the doll will
look for the candy.



PASS: choose the first box


The child knows the doll had not seen the candy move,
and therefore had a false belief



Human 3
-
year
-
olds generally fail the test


5
-
year olds almost always pass



What about other anthropoids?



Comparative psychologists have devised a number
of experimental procedures that require the subject
to construct what another individual knows


Tomasello & Call (1997)


Four chimpanzees, all with extended human interactions,
witness an experimenter put food into one of four cups, all
behind a partition (so the chimpanzees could not tell which
cup contained the food). Another human remained outside
the room, so he did not know which cup contained the food
either. After the naïve human entered the room, the
chimpanzee subjects could choose either the naïve or
knowledgeable human to inform them of the location of the
food.



Tomasello & Call (1997)


3 of the 4 achieved a 70% success rate


BUT, only after 100
-
150 trials



Conclusions:


Human 5
-
year
-
olds would almost certainly do better


Chimpanzees may be learning to solve the test over
time by other means (unintended cueing)


The experimenter may become a conditioned stimulus
for food


Chimpanzees generally FAIL tests of false beliefs


Do apes/monkeys have a concept of self?


This is a prerequisite for theory of mind, but a bit more
basic than false belief



Mirror recognition test


Subject is briefly anesthetized, and a spot of paint is
placed above its eye. When presented with a mirror, if
it immediately touches its face, it demonstrates that it
knows the mirror image is of itself. It has therefore
passed the mirror recognition test.



Mirror recognition test


Monkeys and gorillas invariably FAIL


Chimpanzees sometimes pass/sometimes fail


Chimpanzees
that are raised in human conditions

are the
most likely to PASS



Conclusions:


Experience with human objects plays a role


Under the right circumstances, chimpanzees are likely
to pass, so they almost certainly have some concept of
self



Theory of mind is evident in humans, but there
are no clear evolutionary antecedents



There is a correlation between theory of mind
and general problem
-
solving ability


Suggests ToM is not an encapsulated, domain
-
specific
cognitive ability that evolved to solve a narrow
adaptive problem


Instead, it arose from a need for flexible responses to
complex but generic problems


Anthropoids have expressive faces, along with
a neural network sensitive to differences in
faces and facial expressions


This network is linked to the centers of emotional
processing via the amygdala


So, anthropoids communicate their mood through
facial expression


Anthropoid vocalizations are tied into the same
emotive network


It is very hard for an anthropoid to inhibit
these emotionally
-
based facial responses
because they are involuntary



This may explain their poor performance on
many false
-
belief tests


They may find it impossible to select the object of false
belief because their desire for the reward is very strong
and cannot be inhibited, even if they “know” that it is
the wrong choice for the test


Anthropoids do use tactical deception, but
without theory of mind they are relatively poor
liars


Liars must have the ability to inhibit their emotive
response, one of the key components of executive
functions, which ToM is related to




Conclusions:


Sometime after the evolutionary split from
chimpanzees, our ancestors acquired the ability to
inhibit natural vocal and facial responses


We learned to hide our emotions


The primate evidence suggests that the selective agent
may have been success in tactical deception


Apes’ general inability to suppress automatic
responses leads one to expect an equally poor
performance on tests of working memory



Methodological problems:


Impossible to test recall of lexical items with apes


Most working memory tests require considerable
cooperation by the subject


Apes are usually poor at maintaining attention on one
goal when distracted by another, a clear part of most
working memory tests


Kawai & Matsuzawa (2000)


Tested chimpanzee “Ai” and her ability to remember
the location, on a screen, of a set of sequential integers.
She had already learned to recognize the integers 0
-
9,
and ordered the series while all the integers were
visible. This was done so only her
spatial working
memory
would be tested. The memory portion began
after she selected the first integer in the series, at which
point the remaining integers were masked.



They found that a chimpanzee’s working memory
capacity was 5 items



Kawai & Matsuzawa challenge the “magic
number seven” for human spatial memory


Suggest that chimpanzees are closer to us than many
think



Chimpanzees have a shorter short
-
term
memory capacity than humans


but, perhaps
not by much