Primate intelligence

Anthropology 1:Introduction to Physical Anthropology

Lecture 12 – 4/5/10:

Primate Intelligence

SMC Spring 2010

Rebecca Frank

The main question

Why are primates so smart?

The main question

Why are primates so smart?

• Big brains are costly: metabolism alone consumes 20% of daily energy budget in humans

• If it weren’t good for something, selection would eliminate it…

• What are the benefits that lead to the evolution of large brains / intelligence in primates?

What is “Intelligence”?

• Intelligence not just one thing that you have more of or less of

• Some animals quite smart at limited skills, e.g., memory, navigation, communication

• Many psychologists think “intelligence” = adding together of more and more specialized skills

Nutcrackers, chickadees:

spatial memory

Buntings: celestial

navigation

Bees: waggle dance

Monkeys and apes have big & complex brains

Galago

Rhesus

Chimpanzee

Relative brain size

Primates

Why are costly brains worthwhile?

• Our brains are expensive Make up 2% of body weight Consume 20% of metabolic energy

• Some animals get by with tiny brains

• What are the benefits of a big neocortex? Learning Problem solving

Why be flexible?

• Built-in behavioral strategies work in many situations

• When conditions are stable, little need to learn new things

• Experimentation can be costly

Change and unpredictability may favor flexible problem solving

Flexible Problem Solving

• Cognitive abilities evolve to solve the adaptive problems a species faces

• What are the adaptive problems that seem to have been most important in the evolution of primate intelligence?

• Many theories have been proposed. We will discuss two main ones:1. Cognitive skills evolved primarily to solve ecological

problems (the ecological intelligence hypothesis)2. Cognitive skills evolved primarily to solve social

problems (the social intelligence hypothesis)

Learning and problem solving may also be useful in other contexts too

• Solving complex ecological problems Processing inaccessible food items Locating and remembering food sources Navigating between food sources

• Solving complex social problems Keeping track of kin Keeping track of relative rank Remembering benefits given & received Manipulating rivals Managing coalitions

Testing Hypotheses

• Are ecological or social factors better predictors of brain (especially neocortex) size?

Ecological Intelligence Hypothesis

• Finding food is complicated Where is it? What is edible? When will food be available? How to get from one food site to another How to process food

• Two sub-hypotheses: Frugivory Extractive Foraging

Ecological IntelligenceHypothesis 1: Frugivory

• Exploiting short-lived, patchy food resources (fruits) may have favored special cognitive skills in primates

• Frugivory demands: Knowledge of fruit properties Complex spatial representations Good memory

What do primates know about fruit?

• Japanese macaques know Fruit grows on trees, candy

doesn’t When food is available Properties of food

• Howler monkeys cope with toxins

Many plants produce toxins as protection

Howlers are picky eaters Howlers select leaves low in

toxins

akebi fruit

What do primates know about maps? (Spatial representations)

• In tropical forests, huge diversity of plant species

• In savanna habitats, very large ranges

• “Cognitive map”: mental representation of location, availability, and quality of things in environment

Primates would like google maps…

• Primates seem to know What is edible Where food sites are located When food will be available How much food is available

• Example: Tamarins in Peru Feed on 100’s of different trees Some species fruit synchronously Tamarins visit many trees each day 70% of time move to nearest tree of same species

that was not depleted Don’t revisit trees

Does frugivory correlate with large brains?

A little, but not strongly

Looking at the correlation between the color vision portion of the brain and neocortex, the correlation is stronger

• Extent of frugivory may be related to brain size Frugivores tend to have bigger brains than folivores

Barton 1998

- Parvocellular cells process wavelength & detailed color information

- Large neocortex related to:

- Diurnal activity- % frugivory in diet- Group size

Ecological IntelligenceHypothesis 2: Extractive Foraging

• Exploiting foods that are difficult to process, may have favored special cognitive skills in primates

• Extractive foraging demands: Consumption of difficult-to-process foods Complex, multi-step activities Fine motor skills

Examples of extractive foraging

• Baboons dig up underground food



• Capuchins extract food from Eggs Rotten wood Under bark Hard shelled nuts Spiny, sticky pods



• Capuchins extract food from Eggs Rotten wood Under bark Hard shelled nuts Spiny, sticky pods

• Aye ayes extract insect larvae Insects burrow into wood, lay eggs Tap tree trunk to locate larvae Gnaw on branch to make pit Use 3rd finger to extract larvae

• Orangutans eat durian, neesia fruits Protected by tough or spiny shells Pungent interior


• Mountain gorillas’ foods are abundant, but well defendedbamboo

wild celery

thistles


• Chimps eat many extractive foods

Chimps fish for ants in tree nests




Chimps fish for termites



Chimps extract honey

West African chimps use rocks to bash open hard-shelled nuts



Not really

Does use of extractive foods correlate with large brains?

Other problems with ecological intelligence hypothesis

• Extent of frugivory related to brain size

Frugivores have bigger brains than folivores

• But, extractive foragers include: aye-ayes (relatively small brain) apes (relatively large brain)

• And, small-brained animals: cognitive maps navigate long distances forage efficiently

Social Intelligence Hypothesis

• Dunbar: “social intelligence”

• Humphrey: “social chess”

• Byrne & Whiten: “Machiavellian intelligence”

• Primates live in relatively large groups• Primates track social information

Identity Group membership Kinship Dominance Alliances

• Primates know about own relationships• Primate know about relationships of

others

Social challenges may favor large brains: Social Intelligence Hypothesis

Primates recognize others as individuals and keep track of group membership

• Know members of own group

• Respond aggressively to strangers

• Know ranges of neighboring groups

• Know individual members of neighboring groups

Social Intelligence

Monkeys seem to know a lot about their own relationships

• Distinguish kin from nonkin

• Give submissive signals to dominant animals

• Recruit support from those most likely to support them

Social Intelligence

Social IntelligenceMonkeys know about kinship

relationships of others• When vervet infants

scream, other females look toward mother

• After fights, vervets reconcile with kin of former opponents

• Vervets redirect aggression to kin of former opponents

Social Intelligence

Triadic awareness of rank & friendship in some species

• Is A better friends with B than A is with me?

• Matters if I have a fight with B and ask A for help!

• Capuchins & baboons have triadic awareness of this kind

A

B

Self

?

Social IntelligenceBaboons know something about others’ rank

relationships• Grunt is affiliative call, scream is distress

call• Baboons can recognize others’ calls• HRF make LRF scream, but• LRF never make HRF scream• Play normal sequence of calls:

HRF grunt, LRF scream• Play unlikely sequence of calls:

LRF grunt, HRF scream• Baboons react strongly to unlikely

sequence

Social Intelligence

Knowledge of others’ relationships useful when fights occur• Able to predict who will win contest• Able to predict who will support whom• Able to predict who will intervene against whom• Able to predict who will be effective ally

Social Intelligence

Monkeys can predict what others will do

• Macaques and baboons often grunt when they approach others

• Grunts are reliable predictor of peaceful interaction

• Grunting facilitates friendly contact

• Grunting facilitates infant handling

Does this mean monkeys can read other monkey’s minds?

A special kind of intelligence

“Theory of Mind” or “Mindreading”

• The ability to infer what others think, want, or believe

• And the ability to use this to understand and predict their behavior

• Good evidence that humans have this

• Other primates?

Theory of Mind• In humans, ToM develops in early childhood• Common experiment to test for ToM

Show child M&M tube Ask what’s inside Child will guess “M&Ms” Show child tube contains pencil Adult comes into room Ask child what adult will think is in tube Up to age 3, children say “pencil” After 3-4, children say “M&Ms”

• Many other tests of this• Autism may be a deficit specifically in theory of mind

Monkeys appear to know relatively little about what others know

• Vervet mothers don’t warn infant about dangerous things that they see, but infant doesn’t see

• Don’t do well on tasks that require taking another perspective

• Don’t practice deception (often)

• But: we might not have devised a good way of testing ToM in monkeys; this happened with apes

Theory of Mind

Theory of Mind

Apes may know more about what others know

• Recognize self in mirror

• Can discern others’ intent

• Alert others to dangers they haven’t seen

• Can deceive others

• Political maneuvering

Do Chimps have theory of mind?(Povinelli et al. 1996) Test whether seeing = knowing

• Chimps allowed to chose which of two humans to beg from

• Consistently prefer to beg from a forward-facing human

But they do not prefer…• Human w/eyes open to human w/eyes closed• Human w/blindfold over mouth to human w/blindfold over eyes• Human w/bucket on shoulder to human w/bucket over head• Human w/back turned while looking over her shoulder at the chimp to

human w/back turned while looking away from chimp

But: chimps are sensitive to what others know in food competition

• Brian Hare and colleagues devised a test of theory of mind using food competition

• In chimps, dominant will always get food from subordinates

• Hare et al. placed food so subordinate could see it, but dominant could not – and subordinate knew dominant could not

• Subordinate would take food only when they knew dominant could not see it

Dominant

Subordinate

Food

Ecological Realism

• Often, lab tests like Povinelli’s are poor tests

• Don’t look at skills being used in ecologically realistic contexts in which they evolved

Other contexts of mindreading we haven’t studied much…

• Cooperative hunting

• Stalking prey

• Avoiding predators

Apes’ cognitive abilities are hotly debated

• Some think apes have considerable knowledge of others’ minds

Mind-reading Deceit Compassion & empathy Imitation Moral sentiments

• Others think apes have very little knowledge of others’ minds

Sophisticated social learning capacities But little true understanding of others’ minds

Testing Hypotheses

• Are ecological or social factors better predictors of brain (especially neocortex) size?

Figure 09.07c

Does social complexity correlate with large brains?

Yes: better than with frugivory or

extraction

Except…Social intelligence hypothesis doesn’t explain why apes are smarter

than monkeys

• Apes all live in relatively small groups Chimp and bonobo groups rarely > 50 Gorilla groups < 20 Orangs solitary

• What favored evolution of enhanced cognitive abilities in apes? Apes do use lot of extractive foods Some foraging skills take long time to learn Big brain may be linked to foraging challenges

Complete explanation may require multiple selective pressures

Big brains may also be linked to particular types of social challenges

• Generally larger neocortex ratio as clique size (within a social group) increases

• Simians use more “computing power” for the same clique size as prosimians

• Terrestrial simians more similar to apes than arboreal simians

• Hominoids use more “computing power” for the same clique size as simians

Kudo & Dunbar 2001

Brain size may be the result of selection for flexible behavior in BOTH ecological & social domains

• Compare “executive brain” ratio

Innovation - novel solutions to social & environmental problems

Social learning - learn skills and information from others

Tool use

Laland & Reader 2002

So which is it? Ecological or social intelligence that drove primate brain growth?

• Answer isn’t clear

• Unlikely to be one or the other

• Both likely operating at the same time or in alternation over evolutionary history

• How does the intelligence of species in other taxa inform this question? http://www.youtube.com/watch?v=R6KvPN_Wt8I

Education

Primate intelligence