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23 Φεβ 2014 (πριν από 3 χρόνια και 5 μήνες)

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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

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

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

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

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

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
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




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

eating) anthropoids have smaller
brains and neocortices than


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

This requires a heavy metabolic investment in

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

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

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

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

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

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

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

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

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

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

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

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

These areas have been linked to apes’ more complex

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

known as tool
users and tool

Habitually use tools to access hard
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

“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

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

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


more than two individuals


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

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

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


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

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

This is

deception because the behavior
was tailored to the immediate circumstances

Many organisms use deception, but not

(camouflage, or feigned injury by mother birds)

Tactical responses are impressive solutions to

We cannot over
interpret them

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

Humans, however, regularly rely on another

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
olds generally fail the test

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

Tomasello & Call (1997)

3 of the 4 achieved a 70% success rate

BUT, only after 100
150 trials


Human 5
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

that are raised in human conditions

are the
most likely to PASS


Experience with human objects plays a role

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

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


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
and ordered the series while all the integers were
visible. This was done so only her
spatial working
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

Chimpanzees have a shorter short
memory capacity than humans

but, perhaps
not by much