Evolution of Intelligence
• Ecological and social factors
• The relationship between brain size and intelligence
• Measures of brain size
Ecological Selection Theory
Intelligence developed in response to environmental demands.
Foraging for food, hunting, and tool use require intelligence. Obtaining
food presents a cognitive challenge as the location and variations in
sources of food must be remembered. Food supplies are often
unpredictable and the capture of food may require complex hunting
strategies.
RESEARCH EVIDENCE FOR ECOLOGICAL THEORY
• According to the dietary hypothesis, primate species whose food supply is
patchily distributed need larger brains than primate species eating food that is
more widely available, due to the greater demands on their memory systems
when trying to locate food. Fruits are usually more patchily distributed than
leaves and so frugivores (fruit-eating primates and other species) should have
larger brains than folivores (leaf-eating primates and other species), and CluttonBrock and Harvey (1980) found this to be the case.
• According to the mental maps hypothesis, species that cover a wide area in their
search for food (large range size) and/or spend a large proportion of the day in
foraging will have larger brains than those species that cover only a small area
because they will need larger-scale mental maps. Research evidence on foraging
suggests that mammals do have cognitive maps of food sources. This supports a
link between intelligence and food acquisition.
RESEARCH EVIDENCE FOR ECOLOGICAL THEORY
• According to the extractive foraging hypothesis, species that have difficulty
in extracting food (e.g. they have to use tools to gain access to it) should
have larger brains than those having immediate access to food. Tool use is
very limited; only chimps, orang-utans, and humans routinely use tools,
which can be linked to their higher intelligence. This supports the
ecological theory as it suggests that intelligence is related to more complex
foraging strategies.
• Humans’ diet is more varied and complex than the herbivorous gorillas and
orang-utans and consequently the digestive systems differ. In humans the
small intestine takes up the most space, whereas in gorillas and orangutans the colon does. This shows that the food supply exerted selective
pressures on the digestive system and supports the theory that it may have
done the same to the brain.
RESEARCH EVIDENCE AGAINST THE ECOLOGICAL
THEORY
• Dunbar (1998) reported across 20 primate species that there was
essentially no correlation between range of foraging and the size of
the neocortex and so contradicts the mental maps hypothesis. He
also did not find a relationship between neocortex size and
percentage of fruit in the diet and so contradicts the dietary
hypothesis. He also found that there was no relationship between
complexity of extractive foraging and relative neocortex size and so
contradicts the extractive foraging hypothesis.
• The social theory may provide a more convincing explanation of the
development of human intelligence as dealing with social problems
probably provides more of a cognitive challenge than finding food.
RESEARCH EVIDENCE AGAINST THE ECOLOGICAL
THEORY
• There is not a clear association between tool use and intelligence. For
example, 150,000 to 300,000 years ago was a time of rapid brain
growth in humans, however, tool manufacture did not show a parallel
growth. Between 300,000 years ago and today human brain growth
has been slight but the advancement of tools/technology has been
enormous. Consequently, tool use did not exert a direct selection
pressure on intelligence.
• A key weakness of the foraging theory, as a basis on which to judge
intelligence, is that animals with brains much smaller than humans’
successfully use cognitive maps and hunt.
Write 40 words on Ecological Selection
Theory
• Ecological Selection Theory environmental demands. Foraging for
food, hunting, and tool use require intelligence. Dietary hypothesis,
Mental maps, extractive foraging hypothesis and digestive systems.
Against: Dunbar (1998) range of foraging and Neocortex size. Social
explanation. Brain size tools and timeline. Smaller brains and foraging.
Social complexity
• According to the social brain hypothesis, intelligence and brain size
will tend to be greater in those species having complex social
structures. Intelligence developed in response to the demands of
group living. The social environment presents a cognitive challenge as
a Theory of Mind is needed. That is, the individual must have selfawareness and an understanding that others’ intentions, viewpoint,
thoughts, and emotions are different from one’s own in order to
predict the behaviour of others. They will also have an evolutionary
advantage if they are able to use tactical deception and detect
cheating in others (Machiavellian intelligence). Social complexity
includes the need for deception, the formation of coalitions, cooperative strategies, and mating strategies.
RESEARCH EVIDENCE FOR SOCIAL
COMPLEXITY
• Research on self-recognition supports the Theory of Mind. The mirror test involves
applying a red mark to an animal’s forehead. Animals with a self-concept should touch
this mark when they look in the mirror. Chimps and orang-utans reliably demonstrate
self-recognition, whereas lower primates and non-primates do not. Theory of mind
develops in humans during infancy.
• Another aspect of the Theory of Mind is the ability to deceive and recognise deception in
others. This is called Machiavellian intelligence and is adaptive as the individual has much
to gain from being able to deceive and cheat others without raising suspicion.
Observational evidence suggests that only the higher primates show tactical deception.
This supports the social theory that intelligence is a result of social complexity.
• Dunbar (1998) correlated both environmental and social complexity with the size of the
neocortex, the area of the brain associated with higher order thinking. No relationship
was found between neocortex size and environmental complexity, whereas a strong
positive correlation was found between this and group size as an indicator of social
complexity.
RESEARCH EVIDENCE FOR SOCIAL
COMPLEXITY
• The fossil record provides evidence that the size of the human social
group has increased as we have evolved over time—from Homo
sapiens co-habiting in groups of 150, to the much larger villages and
towns of agricultural man. As the social group increases, so does the
need for more complex interpersonal skills, supporting the theory
that intelligence is required for success and survival within the group.
• Schillaci (2006) found among several primate species that those
having the largest relative brain sizes had monogamous mating
systems. Superficially, it looks as if this finding doesn’t fit the social
brain hypothesis. However, it can be argued speculatively that
primate monogamy involves more complex social skills than
alternative mating strategies.
RESEARCH EVIDENCE AGAINST SOCIAL
COMPLEXITY
• There is great diversity in the social systems of primates with a Theory
of Mind. Orang-utans have a Theory of Mind and are thought to be
intelligent but do not live in large social groups, which challenges the
social complexity theory.
• Social groups may exist without knowledge of others’ minds (e.g.
ants) and so intelligence is not inextricably linked to social living, as
the Theory of Mind and the Machiavellian hypothesis suggest.
RESEARCH EVIDENCE AGAINST SOCIAL
COMPLEXITY
• Given that many apes do live in social groups, much larger brains
should be found in apes and monkeys if intelligence had a social
origin. The encephalisation quotient (EQ) for primates is 2.34 and the
EQ for humans is 7; the proportion of the cortex to the rest of the
brain is 50% in primates and 80% in humans. Therefore we would
expect primates’ brains to be two to three times bigger if group living
was the main factor in the development of intelligence.
• According to Byrne and Bates (2007), we shouldn’t exaggerate social
skills. The enlarged neocortex improves perception, learning in social
contexts, and long-term memory. Thus, these may contribute more to
social complexity than social skills.
EVALUATION OF ECOLOGICAL AND SOCIAL
THEORIES
• Face validity. Both ecological theory and social theory make sense as
both food acquisition and living in groups do present cognitive
demands and do enhance survival and reproductive potential.
However, Dunbar’s (1998) research presents strong evidence that
social factors drove the evolution of intelligence. When we consider
numerous primate species, several aspects of social complexity (e.g.
group size; deception; mating strategy) predict brain size (especially
relative neocortex size). It is thus unlikely to be a coincidence that the
human species has both relatively the largest neocortex of any
species and is also the most intensely social species.
• Anthropomorphic measures of intelligence. There are great
difficulties in measuring and interpreting animal intelligence. Consider
the difficulty we have in creating a culturally fair test of IQ in humans
to appreciate the even greater difficulty of devising a species-fair test
of intelligence across animals and humans. Thus, the research
evidence may lack validity as the measures of intelligence may lack
accuracy, as most research relies on indirect measures of intelligence
such as neocortex size.
• Neocortex size is not synonymous with intelligence. Neocortex size is
not a direct measure of a species’ intelligence, and so we may not be
assessing intelligence very well.
• Difficult to operationalise and so test foraging and social complexity.
It is difficult to compare the cognitive or intellectual demands of
finding food across numerous species leading very different lives in
very different kinds of environment. This means the values assigned
to foraging complexity may not be valid and this may have affected
the correlational findings. Similarly, it is difficult to measure social
complexity, group size, and mating strategy may not be valid
measures of this.
• Cause and effect. The research evidence on ecological and social
factors identifies associations, which do not indicate cause and effect.
Consequently, conclusions are limited to “links” rather than causes.
• Direction of the effect. It cannot be established which came first:
varied diet or intelligence; large social groups or intelligence. It may
be that better diet and group living were consequences of the
development of intelligence. In which case, what caused intelligence
in the first place is not clearly established.
• A chance mutation. Human intelligence may be the result of a chance
mutation that resulted in bipedalism and so freed our hands to forage
and create tools. Brain size and intelligence would be a consequence
of better diet.
neocortex
• a part of the cerebral cortex concerned with sight and hearing in
mammals, regarded as the most recently evolved part of the cortex.
(Back)
Encephalization quotient (EQ),
• Encephalization quotient (EQ), or encephalization level is a measure
of relative brain size defined as the ratio between actual brain mass
and predicted brain mass for an animal of a given size, which is
hypothesized to be a rough estimate of the intelligence or cognition
of the animal. (back)
Brain Size
• Encephalisation Quotient (EQ)
• Lynn – brain size has increased 3 times suggesting larger brain larger
intelligence.
• Willerman et al Brain volume and IQ found a positive relationship
• Narr et al : Cortical thickness and IQ led to a positive relationship.
• Sassaman and Zarler studied children with abnormally small brains
and found that 40% were not retarded. Therefor brain size may not
reflect intelligence.
Evaluation
• IQ is flawed only measures one type of intelligence.
• Crows have small brains but use tools (do have a large cortex)
• Cortical Neurons reflects the speed of information processing so the
more the better. Although humans posses the most possibly not
enough to explain intelligence.
Nature/nurture.
• Nature/nurture.
• The evolutionary explanations over emphasise the role of nature and
ignore nurture. It is not a question of nature or nurture, as
indisputably an interactionist perspective must be taken. However, as
the evolutionary explanations ignore nurture this is a key weakness.
Multi-perspective.
• Multi-perspective. Evolutionary explanations need to be considered
in combination with other explanations. Both biological and
psychological factors interact in the development of intelligence and
so a compromise position such as the diathesis–stress model is
needed, which accounts for the influence of genetic predisposition
and environmental experience.
Males are better!
• In one study, scientists converted the SAT scores of 100,000 17- and
18-year-olds to a corresponding IQ score and found that males
averaged 3.63 IQ points higher than the females [source: Jackson,
Rushton]. The study, did, however, use about 10,000 more females
than males, which may have affected the average, but the study's
authors believe that the greater the brain tissue, the greater the
ability for cognitive processing
• But seriously
Twins and how they help
• Monzygote (one egg). Genetically the same so should have same
intelligence (genetic). If they have the same upbringing then hard to
prove environmental or genetic factors but adoption or being brought
up apart can show if one is more important than the other.
• Zygotic twins: (50%) Different eggs. Brought up the same may show
the environmental factors have greater influence or in fact that
genetic predisposition does.
And finally
• Evolutionary factors in the development of human intelligence, for
example, ecological demands, social complexity, brain size
Essay
• Open Book.
• Discuss research into genetic and/or environmental factors associated
with intelligence test performance. (8 marks + 16 marks)