Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

1: INTRODUCTION

2

2: STUDYING BEHAVIOUR SCIENTIFICALLY

3

3: PRIMATE DIVERSITY AND ECOLOGY

4

4: PRIMATE MATING SYSTEMS

9

5: PRIMATES TO HOMININS

12

6: THE RISE OF MODERN HUMANS

17

7: ORIGINS OF MODERN HUMAN BEHAVIOUR

20

8: HUMAN VARIATION AND “UNIVERSALS”

25

9: RECIPROCITY AND SHARING

29

10: COOPERATION AND KIN

33

11: SEXUAL SELECTION AND HUMANS

37

12: HUMAN MATE CHOICE

40

13: HUMAN PARENTAL CARE

43

14: HUMAN LIFE HISTORIES

45

15: THE EVOLUTION OF HUMAN INTELLIGENCE

49

16: COGNITION AND THE MODULAR MIND

54

17: EVOLUTION OF LANGUAGE

58

18: EVOLUTION AND CULTURE

62

19: EVOLUTIONARY MEDICINE

65

1: INTRODUCTION
Studying humans
● Social sciences/humanities perspective vs
...
With birds, between size
and flight manoeuvrability)
○ Darwinian evolution
■ Living individuals are descendants of other individuals that lived in the
past
■ Evolution occurs through cumulative change over a long period of time
■ New forms occur via splitting of lineages
■ Natural selection is an engine of change
Challenging the model
● Genealogies
○ Fossils
○ Living forms
○ Biogeography
● Pattern of inheritance + the strength of selection should = different degrees of
evolutionary change
● Differences between organisms should reflect their niches
○ Eg
...
Optimality (utility) theory
○ Eg
...
Thorndike, Watson, Skinner)
○ Based studies on controlled laboratory experiments on a small range of
animals
● Ethologists (eg
...
Studies of animal intelligence
● Ethology
● Behavioural ecology
● Applied
○ For purposes of welfare research and animal welfare (studious)
● Behavioural biology is the term commonly used now
Tinbergen’s 4 Whys
● Proximate: explanations for the existence of behaviours over an animal’s lifetime
○ Development (ontogeny)
■ How did the behaviour develop in the organism’s lifetime?
● Eg
...
While hunting or grooming
● Growth rate
● Reproductive effort
○ Primates require:
■ Carbohydrates (produced by plants)
■ Amino acids (protein)
■ Fats and oils (from seeds, insects, and animal prey)
■ Vitamins and minerals
■ Water
○ Primates must avoid toxins such as those found in adult leaves
○ Insectivores:
■ Small body size
■ High, sharp cusps on molar teeth
■ Many undifferentiated teeth
■ Simple digestive system
○ Foliovores:
■ Large body size
■ Small incisors
■ Sharp, shearing crests on molars
■ Enlarged, well-developed digestive system
○ Frugivores:
■ Medium body size
■ Large, broad incisors
■ Low-cusped, relatively flat molars
■ Relatively large digestive system, but not specialised like that found in
foliovores
○ Gummivores:
■ Relatively small body size
■ Long, robust incisors to tap directly into the phloem of plants
■ Some have claws (Callitrichids)
○ Diets and home ranges

■

●

●

●

How does the diet of a primate impact its home range?
● Availability of food
○ Leaves and seeds are often more plentiful than fruit
● Seasonality of food
○ Ripe fruit and leaves are not always present
Primate territoriality
○ Some primates are territorial
■ Home ranges do not overlap, and territories are defended
aggressively
■ Territorial in order to defend mates (primarily males) and resources
(primarily females)
○ Some primates are not territorial
■ Home ranges overlap
○ Whether a primate is territorial or not depends on the cost of defending an
area and the benefits of protecting limited resources/mates
Predation
○ Threats from:
■ Big cats
■ Snakes
■ Birds of prey
■ Crocodiles and alligators
○ Defences against predation
■ Interspecific associations, eg
...
In South American forests), and in areas
with few felids or raptors, primates evolve larger body size and
group size (eg
...
Vervet monkeys)
■ Increased group size
● Detection: more eyes to spot a predator
● Deterrence: mobbing behaviour
● Dilution: individual risk of death is lower
Primate sociality
○ Why are primates social?
■ Predator avoidance
■ Feeding competition
● Can defend food patches
● Female distribution is related to resource distribution = female
social groups
■ Can be costly as there is more competition for food and mates, and
disease transmission is more of a risk
○ Social groups
■ Solitary
■ Polygynous (one male, multiple females)
■ Monogamous/pair-bonded

■ Polyandrous (multiple males, one female)
■ Polygynandrous (multiple males, multiple females)
--------------------------------------------------------------------------------------------------------------------------4: PRIMATE MATING SYSTEMS
●
●

Mating systems: the ways animals find mates and care for offspring
Basic rules for mammals (though there can be different variations among primates):
○ Sexual reproduction
○ Female gestation
○ Female lactation
● Language of adaptive explanations:
○ Strategy: evolved behaviours that are a product of natural selection
○ Costs and benefits: trade-offs in reproductive success
Evolution of female reproductive strategies
● Variation in parental care in animals (eg
...
Female baboons with strong social bonds have greater
reproductive success and live longer overall
● Reproductive trade-offs
○ Resources are limited
■ Allocation of energy to one offspring comes at the expense of others
■ There is a trade-off between quantity and quality of offspring
■ Eg
...
The tail feathers of a male peacock
○ Pair-bonds have little male-male competition, so there is little dimorphism
○ Polygynous groups have huge body and canine dimorphism
○ Polyandrous groups have large dimorphism
● Sexual selection
○ Because of high sexual selection in some species, a lot of resources go
towards increasing a male’s mating success rather than going to females to
increase reproductive success
○ Arguably stronger than natural selection, but both may balance out over time
■ Eg
...
Stags during the rut
● Dominant males gain access to females
■ Behavioural flexibility in primates

●

In polygynandrous groups, males establish a dominance
hierarchy
○ Higher ranking individuals have greater reproductive
success
● Infanticide
○ Death of an infant accelerates the return of a female to
sexual receptivity (lactational amenorrhea no longer
has an effect on ability to become pregnant)
○ 85% of deaths follow takeover by a new male
○ Unweaned infants primarily targeted
○ Rarely done by sexually active males in the group
○ In 45-70% of cases, males mated with the same female
○ Infanticide is not reproductively beneficial for females,
therefore they have evolved counterstrategies
■ Paternity confusion
■ Male friendships
● Male protects female in return for
grooming
● Studies show that female stress rises if
the female does not have a male friend
during a takeover
○ Intersexual selection
■ Female choice
● The female selects the most attractive male
● Sperm competition
○ Polygynandrous groups
■ Oestrous females mate with many males, therefore males with larger
sperm volume have a greater chance of fathering offspring
● Selects for testes size
● Investing males
○ Pair-bonding
■ Mate guarding (mates may cheat), eg
...
Marmosets and tamarins often have twins, so the mother
can increase fertility/survival rate by having helpers
■ Humans are cooperative breeders
Naturalistic fallacy
● What we see in nature is not necessarily “correct”
○ Explanations do not equal justifications
--------------------------------------------------------------------------------------------------------------------------5: PRIMATES TO HOMININS
Origin and evolution of mammals

●

Early Triassic period
○ Therapsids
■ 225 million years ago
● Overlapped with the dinosaurs’
■ Warm-blooded, fur-covered reptiles
■ Egg-layers, did not produce milk
■ Around for 30-40 million years
● Late Triassic, early Jurassic period
○ First mammals
■ Dinosaurs ruled
■ Oviparous (laid eggs)
● End of Cretaceous
○ Dinosaurs went extinct, mammals radiated into new niches
Origin of primates
● Angiosperm hypothesis
○ The adaptive radiation of primates occurred with the radiation of angiosperms
(flowering plants) that offered new opportunities and an unexploited niche
■ Omnivores adapted more flexible hands to handle fruit
● Visual predation hypothesis
○ Omnivores adapted orbital convergence (eyes moved from sides of the head
to the front) in order to forage for fruit nocturnally
● Leaping hypothesis
○ Primate biomechanics for leaping and grasping were favoured
● Generalised nocturnal characteristics (large forward-facing eyes, grasping hands and
feet) were favoured
● Terminal branch hypothesis
○ Primates evolved to better meet the needs of an arboreal lifestyle (vision,
leaping, grasping hands and feet)
Evolution of early primates
● Plesiadapiformes
○ Frugivorous
○ No opposable thumbs
○ Nail on one toe, claws on the others
○ Long, narrow snout
○ Small brain
○ Large incisors
● Eocene period
○ Earth was warm and wet
■ Tropical forests spread into North America and Europe
○ Evolution of two types of primates (it is not possible to say which came first)
■ Adapids
● Possible Strepsirrhine ancestor (wet-nosed primates)
● Larger than Omomyids
● Diurnal and quadrupedal
■ Omomyids
● Possible Haplorhine ancestor (dry-nosed primates)

○ Possible tarsier ancestor
● Nocturnal
● Some leapers
Evolution of Haplorhines and Anthropoids
● Evolved in Fayum, Egypt, during the Eocene/Oligocene boundary (33-36 million
years ago)
○ Oligopithecids (anthropoid/ape dentition, 2-1-2-3)
○ Parapithecids (new world monkey dentition, 2-1-3-3)
● Propliopithecids (group with many genera)
○ Propliopithecus
○ Aegyptopithecus
■ 2-1-2-3 (new world monkey dentition)
■ Frugivorous
■ Sexually dimorphic, suggests sexual selection
■ Arboreal quadrupeds
■ Diurnal
■ Relatively small brain
Evolution of the Platyrrhines (New World monkeys)
● Little evidence of NW monkeys during the Eocene
○ Possibly just due to a misleading fossil record
● We do not know how primates moved from Africa to the Americas
Origin and evolution of the apes
● Evolved during the Miocene (5-23 million years ago)
● “Hominoids”
● Changed from a warm and wet climate to dry and cool
● Apes vs
...
8 million years ago, Kenya)
From hominoid to hominin
● What is unique about humans?
○ Bipedal (walk on two legs)
○ Small canines and large molars with thick enamel
○ Large brains
○ Very slow life histories, long juvenile period
○ Language, symbolic culture
○ These human characteristics did not all develop at once
● Sahelanthropus
○ Evolved in Chad, Africa, 6-7 million years ago
○ Hominin characteristics?
■ Foramen magnum (where the spine joins/goes into the skull) suggests
bipedalism
■ Chimpanzee-sized brain
■ Small canines
■ Flat face, large brow ridge
● Orrorin
○ Evolved in Kenya, Africa, 6 million years ago
○ Preferred a mix of woodland and savannah
○ Hominin characteristics?
■ Femur suggest bipedalism
■ Chimpanzee-like teeth
● Ardipithecus kadabba
○ Evolved in Ethiopia, Africa, 5
...
8 million years ago
○ Hominin characteristics?
■ Toe bone suggest bipedalism
■ Canines sharpen against lower premolars
● Ardipithecus ramidus
○ Evolved in Ethiopia, Africa, 4
...
9-4
...
anamensis
○ Evolved in Ethiopia and Tanzania, 3-3
...
anamensis
○ Bipedal
○ Body size dimorphism
○ Partial skeletons found (Lucy) and Dikika child (Selam)
■ Dikika child
● Found in Dikika, Ethiopia, 3
...
2-3 million years ago
○ Preferred wooded grassland
○ Similar cranium to A
...
5 million years ago
○ Cranium
■ Small brain (450cc)
■ Sagittal crest
■ Large teeth
○ Longer legs
○ May have used stone tools
Australopithecus sediba
○ Found in Malapa Cave in South Africa, evolved 1
...

sediba
Paranthropus
○ “The robust Australopiths”
○ Cranial adaptations
■ Enormous back teeth (made for hard-to-chew food?)
■ Sagittal crest, linked to large temporalis muscles (linked to stronger
chewing)
■ Huge cheek bones (linked to stronger chewing)
○ Bipedal
○ Paranthropus aethiopicus
■ Evolved in Kenya, 2
...
8 million years ago
■ Cranial and dental adaptations for heavy chewing
■ Bipedal

■ Extended periods of growth in males
○ Kenyanthropus
■ Evolved in Kenya, 3
...
5 million years ago
■ Cranial adaptations
● Small brain
● Flat face
● Small molars
■ Possible alternatives to hominids evolving from Australopiths
Hominin phylogenies
● There are two common theories
○ Either theory could be correct with current evidence
--------------------------------------------------------------------------------------------------------------------------6: THE RISE OF MODERN HUMANS
Early Homo
● Evolved in Africa, about 2
...
4-2
...
6-1
...
8 million years old
● 4 skulls found (600-775cc brains)
● Homo-like postcrania
● Oldowan stone tools

Homo erectus
○ Discovered in the late 1800s by Eugene Dubois
○ First fossil evidence for an ape-human transitional species
○ Cranial differences with H
...
ergaster and H
...
ergaster in Africa and western Eurasia evolved into H
...
floresiensis?
■ Ancestral lineage of early Homo?
■ Island dwarfism of H
...
sapiens and
modern humans)
○ Oblong skulls
■ Occipital bun
■ Thin-walled
○ Unique teeth
■ Taurodont roots (extra pulp, enabled them to repair themselves)
■ Heavily worn incisors
● Suggests extensive use of teeth
○ Possible increase in meat consumption, use of tools
held between teeth
○ Short and stocky (helped to reduce heat loss)
○ More robust limbs with more developed muscle attachments
○ Wide torso
○ Short arms and legs
The road to Homo sapiens
● H
...
sapiens about 200,000 years ago
○ There are many alternative theories as to how this happened, any proposed
theory could be correct with current evidence
● Morphological features of modern Homo sapiens
○ Large, round skull with high forehead
○ Small face and teeth
○ Protruding chin
○ Less robust postcranial skeleton
○ Long limbs
● Genetic features of modern Homo sapiens
○ Only a 1
...
2 million years ago
● Apes use tools (suggests a common tool-using ancestor)
○ Sticks used to extract insects
○ Sticks used to test water depth
○ Stones used to crack open nuts and shells
● Oldowan tools
○ Model
○ Use of a hammer stone to produce flakes from a core stone, which are then
used as tools
○ Earliest evidence may have been among Homo habilis
■ Tools found at Dikika from 3
...
5
million years ago
○ Oldowan toolmakers were likely all right-handed
Complex foraging strategies in humans
● studies of aboriginal tribes
● food resources
○ collected food
■ fruit, leaves
○ extracted food
■ termites, honey, tubers
○ hunted food
■ vertebrate prey
○ extracted and hunted food tend to be calorie rich but high risk or hard to find
■ very important sources of energy for a species with a demanding,
long, slow life history
● human foraging
○ Hunting
○ tuber extraction
○ hard-to-acquire food
■ require hard-to-learn skills, promoting a long juvenile period
● division of labour
○ by sex
■ men tend to be more involved in hunting
■ women tend to be involved in extractive foraging
● as soon as women become sexually mature, they are pregnant
or nursing for pretty much the rest of their sexual lives

○
●

extractive foraging allows pregnant/nursing women to
contribute to subsistence in a lower risk environment

food sharing
○ in chimpanzees
■ mothers share with infants
■ males share with females that they have recently been associated
with
■ dominant chimps share with subordinates
■ chimps share with individuals who have shared with them in the past
■ small prey is usually not shared
■ large prey is shared with other members of the group
○ in humans
■ juveniles tend to be more consumers than producers
■ middle-aged men and postmenopausal women tend to be the most
productive
Evolution of a slow life history
● humans are socially and technologically specialised for collection of high-gain,
high-risk food
● extractive foraging and hunting require intelligence and learning
○ large brain
○ long juvenile period
○ increased longevity
○ paternal investment
○ reduced dimorphism
Complex foraging in Oldowan toolmakers
● used mode 1 stone tool technology for:
○ carcass butchering
○ Digging
● bone tools found in Swartkrans, South Africa, were most likely used for termite
extractions
Evidence for meat eating
● concentrations of butchered bones and tools
○ bovid bones outnumber others
■ Homo habilis focused on bovids
● Taphonomy
○ Study of what happens to bone after death
■ Eg
...
9 million years ago due to evidence from the Olduvai
Gorge (a stone circle)
■ however, Olduvai was unlikely to have been a home base
● carnivore activity
● limited processing of bone
● very little weathering of bone
● may have been a meat processing site instead
Homo ergaster: tools and subsistence
● Acheulean industry
○ Mode 2 tools
■ Used the core stone as a tool rather than just flakes
○ Bifacial tools, eg
...
For carcass processing
○ Unchanged for about 1 million years
● Meat eating
○ KNM-ER 1808 bones had evidence of vitamin A poisoning
○ Hand axes were plentiful
○ Cut marks on animal bones
○ Pronounced incisors, may have been more beneficial for meat eating
○ May have been able to use fire, allowing them to get more nutrients from
meat, and thus enabling the development of larger brains
Homo erectus: tools and subsistence
● mode 1 in most areas
● mode 2 present in rare circumstances
● may have used bamboo mode 2 tools instead, which are not preserved
○ mode 2 stone tools may only have been useful during glacial periods
Homo heidelbergensis: tools and subsistence
● focused on hunting large game, so created spears and new butchering tools
● diversity of food resources
● mode 3 technology
○ used Levallois prepared core technique
Neanderthal intelligence
● use of language?
○ Had a hyoid bone that enabled speech, but skull was a different shape so
sounds may have been different
● Mode 3 tools (Mousterian, predominantly flint)
● Hunted large game, eg
...
To keep scavengers or disease
away from camp
● Produced personal ornaments, such as necklaces, and may have used natural
pigments to paint their bodies
● Life of a Neanderthal
○ Short life span (maximum of about 45 years)
○ Difficult lives
■ Arthritis
■ Gum disease
■ Injuries
■ Evidence of the injured being cared for by the group, eg
...
Tools)
○ increased social organisation
■ not just by sex/age
○ growth of symbolic expression (eg
...
Ivory, bone, horn and stone
○ variation in tool kits between different populations
○ raw materials transported long distances
■ shows that they knew the properties of different materials
● big-game hunters
● diverse diet
○ range of vegetation
○ not just carnivorous
● evidence of shelters
○ eg
...
Sculptures, cave paintings
■ More efficient foraging and hunting techniques may have meant that
people had more time for art
The origin and spread of modern humans
● Tools
○ evidence of Neanderthals copying Homo sapiens, led to mode hybrids
● revolution or evolution?
○ Some scientists thought that the explosion of art 40,000 years ago may have
been the result of a revolution accompanied by a modern language and
culture
■ However, art has been found in sites dating from the Middle Stone
Age that suggests that art may have just been slowly evolving over
time
The African archaeological record
● mode 3 tool technology developed in Africa during the Middle Stone Age
● mode 5 tool technology developed in the Later Stone Age
○ about 40,000 years ago
○ much more sophisticated tools, such as microliths
● Middle Stone Age
○ Blades
○ Bone tools
○ Composite tools
■ Eg
...
nurture debate, as both have an influence
■ It is difficult to determine the relative contributions of each
○ There is variation both within and between groups
Variation in traits is influenced by single genes
○ When things go wrong, they can almost always be attributed to a single gene
■ Normal characteristics are coded for by a huge complex of genes
○ Genetic variation
■ Eg
...
Non-insulin-dependent diabetes (type 2)
■ genetic basis
■ in normal systems, insulin regulates the uptake of sugar into cells, but
in NIDD individuals, their pancreas does not produce enough/any
insulin
● leads to the buildup of fat deposits
■ adaptive gene for fat deposits in Micronesia
● Micronesians would have been able to build up their fat
reserves before long boat trips
○ Those with the gene were better able to survive, so
they went on to found new populations (eg
...
High rates of carriers of sickle cell anaemia in countries affected
by malaria
● The shape of the red blood cells prevents malaria from taking
a hold
● Carriers are protected from malaria, those homozygous for
sickle cell anaemia die before they can reproduce, and those
without the gene are likely to die from malaria
○ Maintains a high frequency of heterozygotes in the
population
■ Eg
...
The Amish, 200 founders
■ Eg
...
Height
■ Leads to a normal distribution (bell curve) in a population
■ Heritability (estimation of how much variation in a phenotypic trait in a
population is due to genetic variation among individuals in that
population)
■ Environmental covariation (two individuals become alike due to them
living in the same environment)
○ Twin studies
■ Monozygotic (identical) vs
...
Factory workers vs
...
Rat diets
■ Rats have all evolved the ability to eat basically
anything, but individual rats learn what foods in
their environment are safe to eat over time
■ Evolutionary psychology

●

●

●

●

Environment of evolutionary adaptedness (the environment in
which a given adaptation is said to have evolved)
● Humans have lived in small foraging groups for much of their
existence
● Explains strong cheater detection abilities (ensuring fitness)
and common phobias
Is inbreeding avoidance an evolved human universal?
○ Many diseases are homozygous recessive
● Each person has 2-5 fatal alleles, and relatives are likely to
share these alleles
● Inbreeding reduces fitness
■ Many primates leave their natal group once they reach sexual maturity
● Females leave in chimps, males leave in old world monkeys
(closer to apes)
■ Inbreeding avoidance may be a psychological mechanism in humans
● The Westermarck effect
○ People are not attracted to the people that they grew
up with
○ Eg
...
When listening to a foreign language, words cannot
be distinguished
● Grammar rules are deeply ingrained
■ Language has evolved
■ Not just a byproduct of having a complex brain
● Humans are born with fundamental rules of grammar
● Vervet monkeys can associate sounds with meaning
● Koko the gorilla learned American sign language and could
associate movements with meaning and associate different
signs together to explain the unknown
● Kanzi the bonobo can use lexigrams to communicate
● Primates can associate things with symbols but have no
concept of time or intention
Human society and the free rider problem
○ Society
■ Hunting and gathering societies
● Relied on readily available plants and hunted game for
subsistence
● Small (about 40 members)
● Nomadic

●

● Little/no division of labour
■ The domestication revolution
● Domestication of plants and animals for food purpose, resulted
in horticultural and pastoral societies
■ Social organisation
● Domestication allowed people to:
○ Gain greater control over the production of food
○ Improve their lives
■ Dependable food supply changed the structure of human society
○ Free riders and the tragedy of the commons
■ Overexploitation for own benefit
● Lack of trust that they will get their fair share
Nature vs
...
Mating behaviours of soapberry bugs changes depending
on how often their habitat is disturbed

--------------------------------------------------------------------------------------------------------------------------9: RECIPROCITY AND SHARING
●

a human universal is the presence of societies
○ creates problems of public good
The prisoner’s dilemma
● two people (accomplices) are arrested and interrogated
○ Assuming that they are the same in character and relationship, they have two
choices:
■ Cooperate and take the blame
■ Defect and blame the other person wholly
○ The payoff from their choice depends on what the other person has chosen
COOPERATE

DEFECT

COOPERATE

REWARD = 3

SUCKER = 0

DEFECT

TEMPTATION = 5

PUNISHMENT = 1

●

Payoff:
○ If they are unsure, (3+0)/2<(5+1)/2
■ More incentive to defect, 0<1
○ If everyone is known to defect, 0<1
■ No incentive to cooperate
■ Suggests that there should be a greater proportion of defectors in the
population, as defecting is evolutionarily stable
● There is no incentive to cooperate in a defect world, but a high
incentive to defect in a cooperative world

○

Even if everyone is cooperative, 3<5
■ Incentive to defect in a cooperative world
● Model assumes that two people only meet once, so defectors do not have to face
shame
○ Titt-for-tatt vs
...
all cooperate
■ T4T involves cooperating, then do what your opponent did to you
● Requires a substantial probability of interaction
● Drifts into the population, maintains evolutionary stability
● Reciprocal altruism
○ Altruism: doing something nice for someone, but not expecting an immediate
reward
○ Extended relationships between individuals
○ Memory
○ Conditional punishment (even at own cost)
Reciprocal altruism
● “I’ll scratch your back if you scratch mine”
○ Individuals balance reciprocal acts
○ Use many different currencies
■ Grooming
■ Food sharing
■ Coalitionary support
■ Sexual favours
● Criteria for reciprocal altruism
○ Frequent interactions
○ Ability to keep track of actions given and received
○ Support those who supported you
○ Conditions may have applied to humans in early smaller-scale societies
● Eg
...
vervet monkeys and baboons
○ Nonkin individuals provide greater assistance after grooming
Conditions under which reciprocation flourishes
● Individuals must associate for long-enough periods of time to develop reciprocal
interactions
● The likelihood of one individual performing some social exchange with another
should be predicted on the basis of their past associations
● The roles of giver and receiver should reverse at least once
● The short-term benefits to the recipient are greater than the costs to the donor
● Givers should be able to recognise and expel cheaters from the system
Indirect reciprocation
● Trivers (1974)
○ Argued that an altruistic act need not necessarily be reciprocated by the
person directly assisted but can be returned indirectly by other individuals

■

Eg
...
by a sticker or badge indicating
their actions)
○ Many of the classic studies used as evidence are eurocentric, and focus on
students
■ Possible bias and lack of validity
○ Low and Heinen (cited in Alcock, 1993)
■ Reported that students are significantly more likely to give to charity if
they receive a pin or tag that advertises their participation
○ Mulcahy (1999)
■ Observed who gave money to beggars, then interviewed mixed-sex
couples after the male had donated money
● Males at the early stage of a relationship were more likely to
give that those in a long-established relationship
○ The act of giving when accompanied by a female is to
do with demonstrating one’s generosity to a potential
partner
An alternative theory
● Gintis et al (2003)
○ Argues that kin selection and reciprocity theories do not explain why
cooperation is frequent amongst unrelated individuals in non-repeated
interactions when gains are small
● Strong reciprocity: the predisposition to cooperate with others, and to punish those
who violate the norms of cooperation, at some personal cost, even when such costs
may not be repaid
○ Fehr and Gachter (2002)
■ When asked to play a game for monetary reward under ‘no
punishment’ or ‘punishment’ conditions, punishment of
non-cooperators substantially increased the amount that individuals
invested for the good of the group
○ The concept of fairness lies at the heart of many human social interactions
and can be modelled using the ‘ultimatum game’
■ A participant is given a sum of money and told they can keep it
provided that they split the sum with another individual

●

The participant has to make a one-off offer between 0-100% of
the total sum to the other person, no haggling is allowed
● If the second person agrees to the offered sum, both keep
these amounts; if they reject the offer, both receive nothing
■ According to one-off game theory exchanges, we would expect that
the first participant would offer a sum of well below 50%, and that the
receiver would accept any sum as anything is better than nothing
● However, when the game is played, it is typically found that
individuals offer around 50%, and more than half of receivers
do not accept offers of less that 20% (Sigmund et al, 2002)
○ Individuals do not behave completely selfishly but place
a high value on fair outcomes
○ Receivers are prepared to accept smaller ‘gifts’ under
the following conditions:
■ The giver is chosen by better performance on a
quiz
■ The giver’s offer is randomly selected by a
computer
■ Several responders compete to accept a giver’s
offer
● Sigmund et al (2002)
○ Proposed that our emotional apparatus has been
shaped over millions of years of small group living in
which it is hard to cheat more than once and where we
expect conspecifics to notice and remember our
actions
Hunter-gatherer reciprocity
● Reciprocity: an exchange between social equals
○ Common in egalitarian societies
○ Three types:
■ Generalised: someone gives with no explicit expectation of a like gift
■ Balanced: giving and expecting something in return
■ Negative: giving with the expectation of immediate return
● Generalised reciprocity
○ Occurs to some extent in all societies (eg
...
study of return rates of exploited food resources among
the Ache
--------------------------------------------------------------------------------------------------------------------------10: COOPERATION AND KIN
Types of social interaction
ACT BENEFITS THE
RECIPIENT (+)

ACT COSTS THE
RECIPIENT (-)

ACT BENEFITS THE
ACTOR (+)

MUTUALISM (+/+)

SELFISH (+/-)

ACT COSTS THE ACTOR
(-)

ALTRUISM (-/+)

SPITEFUL (-/-)

●

The top two behaviours are predictable, as they are positive for the actor so help to
improve fitness and therefore ability to survive
○ The bottom two behaviours make no evolutionary sense and so are harder to
explain
Altruism
● Altruism: helping other in a way that benefits them but at a personal cost to yourself
○ Eg
...
males sharing food, may eventually allow them to show off
● There is a problem with group-level explanations of altruism
○ Altruism must ultimately favour the individual, not the group, for the tendency
to behave altruistically to persist in the group
○ Group-level explanations do not fit our understanding of evolutionary theory
■ Eg
...
a marking
Green beards (Dawkins)
● A gene has two effects:
○ Produces a green beard
○ Motivates helping behaviour towards those who have a green beard
● May lead to a mutation where an individual grows a green beard but does not help
other with green beards
● Shows that the evolution of altruism is not straightforward
○ How can a gene increase its own frequency, and is there a way of knowing
who has a probability of sharing the same gene?
■ Can make copies of itself
■ Can help copies of itself make copies of itself
Kin selection/inclusive fitness theory
● Hamilton (1964)
○ An allele may spread because it causes its bearer to reproduce or because it
causes its bearer to help others to reproduce who are likely to carry the same
gene
■ Individuals who are likely to carry the same genes are genetic
relatives (have common ancestors)
● Direct (individual) fitness: the ability for a heritable design feature to reproduce itself
by promoting the survival and reproduction of its bearer

●

Inclusive fitness: the ability of a gene (design feature) to cause its own spread either
through its bearer or those having a high probability of sharing the gene, close
genetic relatives
● Technically, we all share genes, but the variation in the few genes that we don’t
share allows for the evolution of kin selection
● Degree of relatedness (r)
○ The probability that an allele present in one individual is present in another
individual, over and above the population average frequency of the allele
○ The probability that alleles sampled from two individuals are identical by
descent
○ Events of mating organise relatedness between individuals
● Hamilton’s rule
○ rb>c
■ R = coefficient of relatedness between actor and recipients
■ B = sum of benefits to individuals impacted by behaviour
■ C = fitness cost to individual performing behaviour
○ If rb is greater than c, the behaviour will spread/evolve
○ Altruism is limited to kin, as the r of nonkin is 0
○ More closely related individuals (higher r) can afford more costly acts of
altruism
Kin biases in behaviour
● Grooming
○ Benefits
■ Hygiene
■ Reinforces social relationship
■ Conflict resolution
○ Costs
■ Time
■ Energy
○ Most instances are between mother and infant (r = ½)
○ Occurs more often between kin than distant kin or nonkin
Kin selection in humans
● Food sharing is more common among close relatives
● Political alliances between kin are more stable than those formed between distantly
related, or unrelated individuals
● The passing on of wealth to lineal descendants (excluding spouses) is far more
common than giving to less closely related or unrelated individuals
● Close relatives are preferentially sought out in times of need and such help is less
likely to be reciprocal
● Relatives typically receive more expensive presents
● Fieldman et al
○ Asked participants to hold a painful position
■ The longer they held the position, the more money they would receive
○ Participants could earn money for individuals differing in relatedness
■ Themselves (r = 1)
■ Parent or sibling (r = ½)

■ grandparent/niece/nephew/cousin (r = ⅛)
■ Unrelated friend (r = 0)
○ Length of time holding painful position increased with increasing relatedness
● DeBruine (2002)
○ Argued that animals should be sensitive to cues of genetic relatedness when
making altruistic decisions
■ In humans, these decisions may be based around facial similarity
○ Participants played a computer game where they had to choose whether or
not they would share money with an individual
■ Opponents were either facially different or manipulated to resemble
their own
■ Showed more trusting behaviour towards opponents who resembled
them
● Human adoption
○ The adoption of unrelated children has been used as evidence against kin
selection, as raising unrelated children will not provide genetic benefits to the
giver
○ Silk (1990)
■ Observed that among Polynesian cultures, a substantial number of
adopters cared for children who were cousin equivalents or closer
● Families who adopted unrelated children tended to be
agricultural families who needed an extra hand
○ Stack (1974)
■ In Chicago, found that the majority of foster children were adopted by
kin
○ Adopting unrelated children is a recent Western phenomenon
■ Alcock (1993)
● Argues that the urge to produce children and look after them is
so beneficial in reproductive terms that it has become deeply
ingrained
Problems for kin selection
- Kin selection does not explain observed incidents of animals helping non-relatives
- Eg
...
vampire bats will feed non-relatives (Wilkinson, 1990)
- Humans will often engage in apparently altruistic acts such as:
- Giving blood
- Donating to charity
- Forgoing reproduction
- Rescuing unrelated individuals (and even animals)
- Sacrificing their lives for moral or ethical principles
---------------------------------------------------------------------------------------------------------------------------

11: SEXUAL SELECTION AND HUMANS
●

Sexual selection: Darwin’s attempt to explain traits that defied natural (viability)
selection
○ Traits that negatively impact fitness rather than improving it
○ Form of selection that accounts for many elaborate traits and behaviours in
organisms
■ Arises from differences in the ability to find and mate with members of
the opposite sex
■ Only occurs when access to the other sex is limiting (ie
...
peacocks,
irish elk)
● Sexual dimorphism in body characteristics can indicate that sexual selection is going
on
○ Eg
...
many female insects (such as the female bush cricket)
gain direct benefits by consuming a portion of the
spermatophore presented to them by males
○ More spermatophores eaten = more eggs laid
○ Indirect benefits
■ Good genes hypothesis: genetically superior mates produce fitter
offspring)
■ Sexy son hypothesis: females that mate with preferred fathers
produce sons that will have high mating success (not necessarily
genes that improve fitness)
Good genes model
○ Elaborated male traits may be indicators of heritable genetic fitness
○ The handicap principle (Zahavi, 1975)
■ Males have a heritable trait to show off that reduces fitness, so only
the males with the best genes can survive despite the handicap
● Females that mate with these males will have offspring with
higher fitness
● Eg
...
Trinidad guppies
● Female guppies are attracted to orange, a response that may
be due to feeding behaviour selecting for the ability to locate
ripe fruit

○

Sexual selection then favours males with a lot of
orange on them

Intrasexual selection
● Usually male-male competition
○ Strategies used to compete with members of the same sex for access to
members of the opposite sex
○ Not often female-female competition as female ornamentation is produced at
the expense of their offspring, which makes them lose fitness
● Eg
...
irish elk
○ Male-male competition can explain the evolution of many morphological and
behavioural traits
■ Eg
...
small “jack” salmon
■ Female mimicry: to distract or interrupt a competitor
● Eg
...
male dendrobatid frogs, male giant water bugs
● Stronger sexual selection on females leads to the expression of secondary sexual
characteristics in females
○ Eg
...
DNA
fingerprinting and microsatellites) allow the direct assessment
of paternity
○ Evidence suggests that polyandry (females mating with
more than one male) is far more common in nature
than was assumed based on behavioural observations
■ Eg
...
in China, both male and female chastity is important, and in
Nigeria, female chastity is extremely important to males
○ Good financial prospects is uniform across all cultures
Male mate preferences
● Youth
○ Female maximum fecundity is at about 26 years old
● Waist-to-hip ratio of 0
...
Hadza, Tanzania
■ Males bring back more food if only their biological children are home,
and less food if stepchildren are home
Grandparental care
● Grandparents can provide dramatic fitness benefits to offspring
● Certainty of parenthood affects amount of grandparental investment
○ Mother’s mother has greatest certainty of parenthood
○ Father’s mother and mother’s father are intermediate
○ Father’s father has least certainty of parenthood
■ 3% possibility that their son is not the father of their grandchild
● Mothers with their mothers alive and living nearby have children earlier, and have
more overall
○ Menopause may stop mothers from reproducing so that they are free to
improve the fitness of their lineage by helping to care for their grandchildren
■ Competition of their own new offspring may interfere with the fitness of
the offspring of their previous offspring
Discriminative parental solicitude
● quality/quantity trade-off
○ Pregnancy is terminated if:
■ Mother is in poor health
● Pregnancy and lactation are costly
● Gambling perspective
○ Mothers will choose to protect themselves (thus
ensuring the possibility of future offspring) over current
attempts
■ Fetus has a genetic defect
■ 78% of pregnancies miscarry
○ Mothers are always thinking about future returns
Parental resource allocation

●

Males must often compete for limited numbers of females
○ Bridewealth: male giving resources to the female’s family
○ Dowry: female giving resources to the male’s family
○ Bridewealth is much more common, particularly in polygynous cultures
● In times of limited resources, some species, eg
...
nonbiological parents
● Stepchildren are usually not given as much parental investment as biological children
○ Eg
...
25 degree of
relatedness (cousins, nieces, nephews)
● Is adoption contrary to evolutionary theory?
○ In Oceania, most adoptions are by close kin
● Proximate mechanisms for adoption
○ Parental instinct tends to be aroused in childless couples
■ Inability to have children is the most common reason for seeking
adoption
■ Many childless couples treat pets like children
○ Some animals, eg
...
testosterone
● Correlated traits
○ Fast life history
■ Reproduce early
■ Small body, small brain
■ Short gestation
■ Large litters

■ High mortality rate
■ Short life span
○ Slow life history
■ Reproduce late
■ Large body, large brain
■ Long gestation
■ Small litters
■ Low mortality rate
■ Long life span
● Other fundamental life history trade-offs:
○ Investment per offspring vs
...
future survival and reproduction
○ Reproduction vs
...
producing sons reduces lifetime reproductive success of
subsequent offspring in pre-industrial Finns)
The expression of trade-offs may depend upon overall levels of available resources
● Car-house paradox
○ With monetary trade-offs, why do people either have a fancy car AND a big
house or neither?
■ Because people vary in levels of overall resources, and people lower
in overall resources are subject to stronger trade-offs
■ Only people with a large amount of resources ever bother to get both
the car and the house
○ Implications for health
■ Individuals with fewer resources are affected by stronger trade-offs,
which affect health more, and the individuals are more subject to
resource stress
Resource allocation in different environments
● General principle:
○ In an unstable environment (population is below carrying capacity (K)),
organisms invest in breeding early and producing small offspring, thus
maximising growth rate (r)
■ “Weeds”

○

in a stable environment (population is at carrying capacity (K)), organisms
invest in provisioning for their offspring, at the cost of producing fewer
offspring, thus maximising competitive ability
■ “Trees”
○ These strategies are called r-selected (weeds, selected by growth rate) vs
...
pygmy elephants (Borneo), pygmy hippos (West Africa), pygmy possums
(Australia), Baka pygmies (Africa), Batak pygmies (Philippines)
○ Why are pygmies small?
■ Live in a dangerous environment (life expectancy is between 16 and
24, compared with 34-48 in non-pygmy hunter-gatherer environments)
● To ensure that enough individuals survive to reproduce,
pygmies reach sexual maturity earlier (fertility peaks at 20-24
compared with 30-34 in non-pygmy hunter-gatherer
communities) at the cost of reduced allocation of limited
resources to growth (determinate growth - pygmies stop
growing at the age of 14 rather than 18, but grow at a similar
rate to non-pygmies)
■ R-selected
■ Hastened maturity is the goal of adaptive evolution, short stature is the
price paid
Proximate and ultimate causes of trade-offs in human health and disease
● Central role of hormones
○ Hormones mediate flow, distribution, rate of consumption of glucose and fat,
among competing physiological functions
○ Hormones implement trade-offs between growth, reproduction, and survival
○ Eg
...
future
offspring, mediated by:
● Nursing and mother’s condition via lactational amenorrhea
(affecting prolactin levels) and by the timing of the introduction
of supplementary foods
○ Influences the timing of the start of the next menstrual
cycle
● Fecundity during waiting time to next conception
○ Poor energetic condition (and low ovarian steroid
levels) are associated with reduced ovulation frequency
■ May produce male-female and mother-offspring
conflict over next conception, with mechanisms
that may become dysregulated
■ Trade-off between offspring number and quality
● Mothers may also benefit from a faster reproductive rate and
shorter interbirth intervals, even when doing so involves higher
offspring mortality
■ Three stages of fecundity
● Rise over the first decade after menarche (slow climb to full
fertility)
○ May be due to selection against high potential
survivorship costs of childbearing for younger females
● Fairly stable from mid-20s to mid-30s
● Decline to menopause at about 50

○

Proximately due to depletion of follicles (number fixed
at birth)
■ Disorders of this process are premature ovarian
failure and polycystic ovary syndrome
○ Ultimately may be due to some combination of:
■ Higher risks of childbearing with increased age
■ Higher risk of death from other causes with
increased age (for self and mate)
■ Benefits from enhancing the reproduction of
one’s children and grandchildren
○ Trade-off between existing and future children, and
future reproduction and survival
● Medical implications of trade-offs in human life history
○ Declines in testosterone with age lead to increased risk of obesity, insulin
resistance, and cardiovascular disease
■ Testosterone supplementation may increase mortality in individuals
under energy limitation
○ Exposure to reproductive hormones (including contraceptives) and older age
at first birth in women can increase the risk of some reproductive cancers
(breast, ovarian, testicular, prostate, uterine, cervical)
○ Hormone physiology and trade-offs may differ between human populations
historically exposed to different selective pressures affecting life history (eg
...
reproduction
--------------------------------------------------------------------------------------------------------------------------15: THE EVOLUTION OF HUMAN INTELLIGENCE
Big brains and long lives
● Longevity via selection on brains
○ Primates are able to learn, but there is no point learning if there is no time to
apply the knowledge
● Primate characteristics
○ Large brains
○ Long childhood
○ Learned behaviours
○ Behavioural flexibility
○ Long lives
● Life history theory
○ Primates have long life histories
■ Slow maturation
■ Large brain
■ Long gestation

■
■
■

Small litters
Long lifespan
Variation within primates
● Monkeys have slower life histories than strepsirrhines
● Apes have slower life histories than monkeys
● Orangutans have the slowest life histories
○ Humans are still brainier
■ Suggests that the correlation between brain size
and longevity is not simple
Evolution of the large primate brain
● Hypotheses
○ Social intelligence hypothesis
■ Social intelligence: the ability to effectively navigate and negotiate
complex social relationships and environments
■ Sociability requires greater awareness for individuals around you and
relationships, therefore brain size increases to enable individuals to
process this wider dimensional world
○ Ecological challenges hypothesis
■ Mental mapping of fruit
● Frugivorous primates can remember where trees are and how
productive they are, allowing them to consume more fruit
○ Primates who evolved this ability had larger brains, and
they were better equipped to survive
■ Extractive foraging
● Exploiting foods that are difficult to get to and process requires
special cognitive skills in primates
○ Behavioural flexibility hypothesis
■ Primates can learn new solutions to problems from others
○ A large brain would allow primates to better cope with both ecological and
social problems
■ Ecological problems
● Processing inaccessible food items
● Locating and remembering food sources
● Navigating between food sources
■ Social problems
● Keeping track of kin
● Keeping track of relative rank
● Remembering benefits given and received
● Manipulating rivals
● Managing coalitions
● Brain structure
○ Frontal lobe
■ Reasoning
■ Decision-making
■ Emotions
■ Personality

○

Temporal lobe
■ Memory
■ Auditory information
○ Cerebellum
■ Posture and balance
■ Coordination of movement
○ Occipital lobe
■ Colour vision
■ Shape recognition
■ Perspective
○ Parietal lobe
■ Memory and recognition
■ Movement, sensation, orientation
○ Hypothalamus
■ Thermoregulation
■ Controls the pituitary gland
■ Autonomic nervous system
■ Controls the basics (eg
...
controls the heartbeat)
○ Human brains are larger and more “wrinkly” than primate brains
■ Wrinkliness increases volume
○ Body size affects the size of the brain, so ratios are used
○ Neocortex ratio
■ Neocortex: most recently evolved part of the brain, involved in sight
and hearing in mammals
■ Correlated with group size in primates (although apes are more
intelligent despite smaller group size)
● Supports the social intelligence hypothesis
■ Higher in fruit-eating primates with larger home ranges
● Supports the ecological hypothesis
■ Not all primates are good at everything
● Eg
...
adult apes
■ Equal ability in physical tasks
■ Humans outperform apes in social tasks
● Human uniqueness
○ Large brain
■ Huge cerebral hemisphere (frontal lobe) compared to most mammals
(Deacon, 1997)
○ Brain is functionally lateralized (tasks are performed by one side of the brain
or the other) in a way which differs from chimpanzees
○ Brain may be metabolically enhanced (Cacares et al, 2003)
■ May include different physiological components (Allman et al, 2005)
○ Humans have 10​14​ neurons in the nervous system, over 2x the number that
chimpanzees have
● Brain reorganisation: expansion of the frontal lobes
○ Schoenemann et al (2005)
■ Suggested that prefrontal white matter is disproportionately larger in
humans than in other primates
○ Allman et al (2005)
■ Von Economo neurons (VENs)
● Recently evolved cell type
● May be involved in the fast intuitive assessment of complex
situations
○ Could be part of the circuitry supporting human social
networks
● Humans shown to have a large number of these
○ Very interconnected throughout the brain
● Functional differences: cultural learning and invention
○ Tomasello and Rakoczy (2003)
■ Argue that there are two (initial) stages of uniquely human social
cognition
● First stage is observable in one-year-olds
○ Have an understanding of others as intentional agents
■ Allows them to take part in pretend play
■ Important as a prerequisite for shared attention
and early social and linguistic learning
● Second stage is ‘theory of mind’ belief-desire psychology
which normally starts around four years of age
○ Dependent on several years of linguistic
communication

■

Early stages of uniquely human social cognition enable the cultural
“ratchet” of social and technological innovation
● Understanding and sharing intentions
○ A species-unique motivation to share emotions, experiences, and activities
with other people
■ Leads to a “species-unique from of cultural cognition and evolution”
○ Especially important when manufacturing of tools became more common
--------------------------------------------------------------------------------------------------------------------------16: COGNITION AND THE MODULAR MIND
●

Swiss army knife analogy
○ Evolutionary psychology
■ The swiss army knife is a flexible tool, as it has a bundle of tools, and
each is well-designed for solving a particular problem
● Similarly, different parts of the brain all have different functions
to handle a range of situations
A modular mind
● Modules of the brain are organised by function
● Modules have been generated by evolutionary processes throughout human history
○ Assumed that they mainly developed during the Pleistocene (2 million years
ago to 10,000 years ago), when our ancestors lived in small kin-based
hunter-gatherer societies
● There are cross-cultural differences
○ Evolutionary psychology predicts that the evolved cognitive mechanisms
(modules) should be context-dependent, as differential inputs (provided by
different environments) should evoke different representational and
behavioural outputs
■ Eg
...
)
○ Few lifestyle options
○ However, it must be considered that there is no concrete evidence that shows
exactly what the EEA was like (Badcock, 2000)
Impact on modern life
● Adaptations to the EEA may now affect modern life
○ Humans have developed psychological mechanisms (and later, culture) to
solve problems related to the lifestyle of a hunter-gatherer

○

Some of these adaptations are not necessarily adaptive to modern humans,
eg
...
lactose tolerance)
● Different populations may lead very different lives depending on their environments
● Tooby and Cosmides (1992)
○ Stated that there is no single EEA, but that each adaptation can be viewed as
a statistical aggregate of selection pressures over a particular time period
Domain specificity
● The more important the adaptive problem, the more intensely natural selection will
improve and specialise the mechanism for solving it
○ Therefore, Darwinian algorithms become domain-specific - they are designed
to solve specific rather than general problems
■ Eg
...
swiss army knife analogy, Cosmides)
● Example: algorithms for social exchange
○ Social exchange behaviour is universal and highly elaborated in present
human cultures
■ Must have been an important feature of our evolutionary history
● Trading tools
● Sharing food
● Making and swapping alliances
● Soliciting help when faced with aggression
● Cooperation in hunting
● Gaining access to mates
● Sharing information about resources
● Sharing social information
■ Chimpanzees engage in similar forms of social exchange and
reciprocation
○ Spotting a cheater
■ The key to success in social exchange is the ability to recognise and
expel a cheater from the system
● Traditional psychology argues that we learn such abilities
through the general purpose process of cultural transmission
○ Suggests that the logic underpinning such behaviour is
generalised

●

○

○

Evolutionary psychology instead argues that we should have
developed specialised cognitive mechanisms for spotting
cheaters in such exchange situations
○ These skills are not generalised - they are domain
specific
Human social exchanges
■ Social exchanges can be viewed in terms of formal logic
● If the traditional psychology model is correct, we should be
equally skilled at all types of formal logic
■ The Wason selection task (Wason, 1966)
● Measure of conditional hypotheses
○ ‘If P then Q’, the logically correct response is ‘P and
not-Q’
● In a typical paradigm, students chose the correct solution less
than 25% of the time
○ Most pick P, and then wrongly select Q instead of not-Q
● Performance is always poor on traditional logic versions of the
task
■ Social contract versions of the Wason selection task
● Cosmides (1985) argued that individuals will be able to detect
violations of conditional rules when such rules represent
cheating on a social contract
○ Eg
...
history of cheating/trustworthiness and
irrelevant information)
● One week later, the same participants recognised the faces of
the cheaters more
■ Stone et al (2002)
● Reported a case of a patient with extensive brain damage
○ Performed as expected on Watson traditional logic
problems, but was severely impaired in Watson social
contract logic problems

■
●

Suggests that reasoning about social exchange
can be neurologically impaired

Can we judge a book by its cover?
○ Yamagishi et al (2003)
■ Identified people who either cooperated or cheated on a game
● Showed their pictures to participants with no knowledge of
their honesty
○ Later asked to recognise the pictures amongst other
unseen pictures
■ Pictures of cheaters recognised significantly
better
■ Argued that cheaters may look different to non-cheaters, and that
people may be able to pick up on subtle facial cues
Interactionism
● Critics often state that evolutionary psychologists are deterministic because they
ignore the role of the environment in shaping human behaviour
○ This is not true, a key assumption underlying evolutionary psychology is that
behaviour is created by gene-environment interactions
■ Eg
...
because we possess
psychological and physiological mechanisms that make us want to do these
things
■ “Feelings” are a mechanism designed by evolution to ensure that the
individual attends to beneficial or harmful stimuli
Domain general and domain specific
● The swiss army knife analogy is more formally expressed in terms of modular
capacities or domain specific
○ It is also possible that general intelligence is also domain-specific
■ Opens the door to the idea that human evolution ended up by
providing us with very open-ended and general purpose physiological
capacities
● General intelligence as a domain-specific adaptation (Kanzawa, 2004)

○

General intelligence creates a problem for the modular view of the human
brain
○ Argues that general intelligence evolved as a domain-specific adaptation for
the originally limited sphere of evolutionary novelty in the ancestral
environment
■ Has accidentally become universally important because we now live in
an evolutionary novel world
--------------------------------------------------------------------------------------------------------------------------17: EVOLUTION OF LANGUAGE
Human language
● Phonemes
○ The human brain splits sounds into meaningful sections (words)
■ Discrete words are an illusion
○ Infants are born with the ability to distinguish all phonemes
○ Humans can decode 10-25 phonemes a second
○ Humans inherently understand grammar rules
● The major transitions (JMS and ES, 1995)
○ Replicating molecules to populations of molecules in protocells
○ Independently replicating genes to chromosomes
○ RNA as genes and enzymes to DNA genes, protein enzymes
○ Bacterial cells (prokaryotes) to cells with nuclei and organelles (eukaryotes)
○ Asexual clones to sexual populations
○ Single-celled organisms to animals, plants, and fungi
○ Solitary individuals to colonies with non-reproductive castes
○ Prelinguistic societies to human societies with language
● What is language for?
○ Helps us to pass on and develop technologies (eg
...
hunting)
○ Allows humans to communicate knowledge about relevant aspects of the
environment
○ Helps humans to identify things with names and description
○ Allows expression of emotions
○ Allows us to remember and use the past, to plan for the future
○ Could we achieve or even think any of these things without language?
○ Language is open-ended, allows for potentially infinite communication
Speech and symbolic language
● Investigation comparing an adult chimpanzee and a 21-month-old child
○ Chimp more advanced in language
○ Six months later, the vocabulary of the child far exceeded that of the
chimpanzee
● Can non-humans develop languages?
○ Washoe the chimpanzee
■ Learned 160 words of ASL

○

Nim Chimpsky the chimpanzee
■ Demonstrated that while primates could learn individual words, they
struggled with grammar rules
■ Criticised for using operant conditioning (rewarding desired behaviour,
punishing undesired behaviour)
○ Koko the gorilla (1971)
■ Understands 1,000 ASl signs and about 2,000 spoken English words
○ Alex the African Grey parrot (1975-2007)
■ Could identify 50 objects, count to 6, distinguish 7 colours and 5
shapes, vocabulary of about 150 words
● Probably operant conditioning
○ Kanzi the bonobo
■ Used symbols that represented language, could respond to 72% of
660 requests
○ Chaser the dog
■ Can identify 1,022 words (names of toys)
When did language evolve?
● Language doesn’t leave a trace in the fossil record, so we can’t say exactly when it
evolved
○ Must be after divergence of gorillas, chimpanzees, etc
...
car is a class of objects with certain properties

○

Generative: a limited number of symbols can generate an infinite array of
novel messages
○ Structured: rules govern the arrangement of words into phrases and
sentences (infinite variety is structured in a limited number of ways)
Understanding language evolution is complex
● Language acquisition/breakdown
○ Developmental psychology, neuropsychology
● Language structure
○ Linguistics, psycholinguistics
● Language change, universals
○ Linguistics
● Models
○ Computer science, robotics, population biology
● Genetic correlates
○ Behavioural genetics
● Animal communication
○ Primatology, comparative psychology
● Fossils, endocasts, artefacts
○ Archaeology, anthropology
● Articulatory physiology
○ Speech sciences
● Neural correlates
○ neuroscience
Gossiping hypothesis
● 2/3s of all conversation is about social relationships
○ Both in developed and hunter-gatherer societies
● Does this kind of language use have any effect on our fitness?
● Does it help our survival rate?
● Does it increase our reproductive rate?
Substitute for grooming hypothesis
● Monkeys and apes are very social and maintain complex relationships through
grooming as a main social interaction
○ Maybe humans have substituted grooming with language to maintain complex
social relationships
Increasing group size hypothesis
● The largest group size for non-human primates is 50-55 in chimps and baboons, and
about 150 for modern hunter-gatherers
○ Primates spend up to 20% of their days grooming, humans would need to
spend 40% of their time to cover such a large group
○ Humans may use language as ‘vocal grooming’
● However, social insects can live in colonies of 30,000 insects and have not evolved
language or grooming
The genetic origin of language
● Early hominids probably began using gestures to communicate intentions within a
social setting
● FOXP2 gene

○
○

Language or speech gene responsible for a major inherited speech disorder
Study of the KE family
■ Over 3 generations, half of the family was affected
■ Inability to form intelligible speech, defects in processing words
according to rules
○ Caused by a single nucleotide mutation on exon 14 of chromosome 7
(10,000-100,000 years ago)
○ Very conserved gene
■ 1 change in 75 million years before the divergence of chimps and
humans, and 2 changes in the 6 million years since that divergence
○ May be critical for the development of modern human speech
● Neanderthals may have been able to do the basics of language
● Vocal anatomy gradually evolved
○ Oral cavity increased in size, giving the tongue more room to move around
○ In chimpanzees and Australopithecines, the pharynx is short, and the soft
palate and epiglottis meet to separate the oral cavity from the pharynx while
breathing
○ In humans, the pharynx is longer, the oral cavity is taller and the tongue is
shorter
■ Longer necks
■ Humans also have a distinct chin, which allows for more varied tongue
movements necessary to articulate the sounds of speech, and
paranasal sinuses, which act as resonating chambers
● Coevolution of language and the brain
○ Wilson
■ Increased brain size = more complex behaviour, which in turn, due to
increased environmental complexity, selects for increased brain size
■ Feedback loops
○ Genetic assimilation: process by which a phenotype originally produced in
response to an environmental condition becomes genetically encoded due to
artificial or natural selection
● Evolution of language
○ Gene evolved 120,000 years ago, recorded culture appeared 50,000 years
ago
○ Incremental language ‘strategies’ produced by different hunter-gatherer
groups may have led to the development of different languages
○ May be the most important synapomorphy in all of human evolutionary history
■ Synapomorphy: a characteristic present in an ancestral species and
shared exclusively by its evolutionary descendants
Human language families
● There are currently 12 extant phyla of human languages
● All cultures have language
○ Currently over 6,000 languages, many are unwritten
● Competition among languages
○ 50-90% expected to go extinct by 2100
○ English and Spanish tend to replace native languages

○

Abrams and Strogatz (2003)
■ Two monolingual (in different languages) individuals mate
● Offspring are bilingual
○ When offspring mate, they tend to only teach their
offspring one of their spoken languages
○ Offspring may drop economically useless languages
● Only monolingual languages may disappear (all speakers are
bilingual)
--------------------------------------------------------------------------------------------------------------------------18: EVOLUTION AND CULTURE
Learning, society and culture
● Intelligence = our ability to learn from our own experiences and the experiences of
others
○ Cultural transmission of learned behaviour eliminates the hazards
encountered when an individual must learn by trial and error to cope with
environmental variables
● Evolution and human culture
○ The new stream of inheritance facilitated by the ability to use language may
have been key in the development of culture
○ Culture: information acquired through social learning
■ Not unique to humans, as lots of other species (eg
...
crows, chimpanzees) use tools
○ Social transmission of information
■ Social facilitation
● Learning by being in the right place at the right time
○ Trial and error by observation
● Eg
...
in response to malaria, dairy
farming, etc
...
unit of cultural information (meme)
● Gene pool vs
...
cultural transmission
● Natural selection vs
...
smoking) have a direct effect on survival and natural
selection may change their frequency
■ Other traits spread solely due to cultural selection (eg
...
innovation
● Random genetic drift vs
...
tools, hunting skills, knowing what is edible and what is poisonous,
rules and activities that sustain cooperation and sharing, attitudes to
inventiveness and conformity, etc
...
marriage norms) influences gene transmission
● Gene-culture coevolution
○ Cultural transmission can modify selection pressures, alter evolution
○ Selection differs by presence/absence of a cultural trait
■ Lactose absorption among adults
● Lactose absorption has a strong genetic basis
○ Dominant autosomal trait
● Correlation between dairy farming and adult lactose absorption
○ Only 20% of adults digest milk, but they are
concentrated in areas with a history of dairy farming
■ Natural selection may oppose culture
● Preference for sons in some areas leads to greater female
mortality before the age of first reproduction (cultural attribute)
● The SRVX “femaleness” gene distorts sex ratios in humans
○ Leads to female bias at birth due to the rarer sex (who
are more likely to carry the gene) producing more mean
offspring
■ Adult sex ratio is unbiased as excess females
are killed off
● Culture profoundly affects the evolution of the sex ratio gene
■ Horizontal cultural transmission may promote group selection in some
environments
● May counter individual selection within groups
Human control over our own evolution
● Less than half of the hunter-gatherers lived to age 20 so they were unlikely to have
more than three or four offspring, and most of those died young too
● In technologically advanced societies, most live past the age of 50 and can reach
their biological capacity of 12-15 offspring unless they choose to limit family size
○ As economic security increases, they tend to do so
Cultural evolution outpaces biological evolution
● One measure of how change continues to affect us is the time is takes to double our
collective knowledge
○ Human minds have become agents of a novel selection mechanism by
consciously choosing among alternatives because of their consequences
(rational decision-making)
Human society and culture
● The entire tradition of the liberal arts is an effort to describe and understand human
society and culture
○ Anthropology and archaeology
○ History and sociology
○ Languages, literature, and the other arts
○ Psychology and philosophy

●

The scientific disciplines went their own way in studying the causes of human
behaviours in the century after Darwin
--------------------------------------------------------------------------------------------------------------------------19: EVOLUTIONARY MEDICINE
Darwinian medicine
● Assumes that our physiological mechanisms are geared towards improving our
fitness
● Asks why the body is designed in a way that makes us vulnerable to infections,
cancer, choking, ulcers, depression, hypertension, diarrhoea, back pain, prenatal
complications, etc
...
the cold virus is not very harmful, but smallpox, cholera, and the ebola
virus are often lethal
● Three general models to explain the evolution of virulence

○

○

○

The coincidental evolution hypothesis
■ Virulence of some pathogens in humans may not have been/be a
target of selection at all
● May be an accidental result of selection on other traits
■ Eg
...
poliovirus normally lives in cells that line the gut, causes no
symptoms, and is transmitted via faeces
● Occasionally, the virus invades nerve cells, which may be
selected for because lack of competition enhances within-host
fitness
○ However, the virus cannot be transmitted to a new host
from nervous tissue
■ Eg
...
HIV-1 is more damaging to its hosts than HIV-2, but it is more
likely to be transmitted because of its high viral load
● Therefore, HIV-1 has become much more common than HIV-2

■

■

A key assumption of this hypothesis is that the pathogen cannot
reproduce within its host without doing some harm (because energy
and nutrients are taken from the host and pathogen waste products
must be removed by the host)
● The host mounts an immune response to eliminate the costs of
hosting the pathogen
○ All else being equal, pathogens with higher within-host
reproductive rates should be transmitted to hosts more
effectively
■ However, too rapid a reproductive rate, and the
host may be so debilitated that transmission
rate is reduced
Messenger et al (1999)
● Examined the key tradeoff in E
...
1%, and
more than 60% of vector-borne
diseases have mortality rates
about 0
...
reading under artificial light
■ Evidence provided by populations that have only recently adopted a
modern lifestyle
● Eg
...
a virus or bacterium
that has evolved with us)
● Mice carry a virus called Mouse Mammary Tumour Virus
(MMTV) that causes the mouse equivalent of breast cancer

○

■

MMTV or a similar virus may cause breast cancer in
humans
■ Wang et al (1995)
● Analysis of 314 breast tissue samples,
38
...
9% of normal breast
tissue samples did
■ Geographical analysis of the incidence of breast
cancer in relation to the distribution of the
mouse species Mus domesticus and Mus
musculus (Stewart et al, 2000)
● Mus domesticus occurs in Western
Europe, Mus musculus occurs in eastern
Europe
● Mus domesticus tends to be more
heavily infected with MMTV
● If MMTV causes breast cancer, rates of
breast cancer should be higher in
Western Europe than Eastern Europe
○ Data fits this prediction
○ Data on MMTV is suggestive, not definitive, and MMTV
has not been isolated from breast tumours and route of
infection is unknown
■ Also, MMTV cannot account for more than 40%
of breast cancer cases, so an alternative
hypothesis must be considered
Breast cancer, like myopia, may be a disease of civilisation
● The monthly menstrual cycle of most modern/western women
is considered normal
○ However, epidemiological evidence suggests monthly
menstrual cycles may increase the risk of breast cancer
■ Breast cancer risk increases with:
● Early onset of menstruation
● Increasing age of first birth
● Decreasing time spent nursing
■ Menstrual cycling appears to elevate the risk of
cancer because the combination of estrogen
and progesterone stimulates cell division in the
cells lining the milk ducts
● More division = more mutations
● Is monthly menstrual cycling normal?
○ Strassmann (1999)
■ Studied menstruation among the Dogon of Mali
● Do not use contraception

●

●

Women aged 20-35 spend little time
menstruating, as they spend their time
either pregnant or experiencing
lactational amenorrhea (no cycling due
to breastfeeding)
○ At any given time, less than 30%
of the Dogon women are
undergoing menstrual cycling
○ Over the course of her
reproductive lifetime, a Dogon
woman experiences about 100
cycles, compared to the 300
cycles of a North American
woman
There is no data on breast cancer rates
among Dogon women, but rates in
comparable populations are only about
1/12th that of North American
populations
○ Alternative contraceptive
regimens that more closely mimic
the ancestral menstrual cycling
pattern may reduce the risk of
breast cancer among North
American women



---