Evolutionary Psychology, Lecture 2
What is Evolutionary Psychology?
Learning Outcomes.
 At the end of this session you should be able to:
 1. Describe the processes of natural and sexual
selection.
 2. Explain the term ‘adaptation’.
 3. Outline the theoretical assumptions underlying
evolutionary psychology.
Opening Thoughts.
 “ Nothing in biology makes sense except in the light of
evolution” Theodosius Dobzhansky.
 “Is it not reasonable to anticipate that our understanding of
the human mind would be aided greatly by knowing the
purpose for which it was designed?” George Williams.
 “Culture is not a mere encrustation upon human nature,
like dirt on a soiled shirt. It is an integral part of it because
human nature can only be expressed through human
culture”. Kenan Malik.
 “If psychology is to take its legitimate place among the
family of life sciences, it must eventually integrate its basic
theories and facts with those of evolution” Rosenthal.
Standard Explanations for
Human Behaviour.
 The Standard Social Science Model (SSSM) has dominated
the social sciences from the 1920’s. It argues:
 1. Humans are born as ‘blank slates’ knowledge and
personality are acquired through culture.
 2. There are no biological constraints on behaviour.
 3. Children learn how to behave learning, socialisation or
indoctrination.
 4. Learning is a general purpose process used in all domains
of knowledge.
 However, Tooby & Cosmides (1994) argued that we cannot
study a behaviour without understanding the original
selection pressures that created the behaviour.
Evolution via Natural Selection.
 The cognitive modules that constitute the human brain are
assumed to have developed via natural selection.
 Evolutionary theory (as devised by Wallace and Darwin)
consists of several simple principles:
 1. 'Principle of Variation': Individuals within a species show
variation in their physical and behavioural traits.
 2. 'Principle of Inheritance': Some of this variation is
heritable.
 3. 'Principle of Adaptation': Individuals are in competition
with one another for scarce resources and some inherited
variations will have survival advantages.
 4. 'Principle of Evolution': as a consequence of being better
adapted to an environment, some individuals will produce
more offspring, who will inherit the same advantages. This
is called 'fitness'.
Sexual Selection.
 Darwin was puzzled by the existence of certain physical
features that do not contribute to survival, and may even
hamper it (e.g. the peacocks tail).
 He realised that such features were governed by sexual
selection - the creation and maintenance of features
essential for attracting the opposite sex, and defending
one’s status.
 Natural selection and sexual selection thus work together.
 Hamilton (1964) reformulated evolutionary theory by
showing that the measure of an individuals direct
reproductive success (fitness) was too narrow a concept.
 He introduced the term ‘inclusive fitness’ - characteristics
will be selected for that improve the chances of an
individuals genes being passed directly, or via relatives.
Adaptive Problems.
 Animals face a series of adaptive problems in their physical
and social environments, e.g. finding a mate; finding food;
avoiding predation; fighting off disease.
 Each of these problems can affect reproductive success
(fitness).
 Each problem has been tackled by adaptive changes in
physiology and behaviour.
 Social scientists accept that our bodies have been sculpted
by evolutionary forces, e.g. we all possess sweat glands for
thermoregulation.
 Evolutionary psychologists argue that our psychological
mechanisms and the resulting behaviours have also been
shaped by the same forces.
 They attempt to construct plausible arguments as to how
our behaviours function as adaptations.
Adaptations.
 Williams (1966) defined an adaptation as
 “a characteristic that has arisen through and been shaped by
natural and/or sexual selection. It regularly develops in
members of the same species because it helped to solve
problems of survival and reproduction in the evolutionary
ancestry of the organism. Consequently it can be expected to
have a genetic basis ensuring that the adaptation is passed
through the generations”.
 Most social scientists try to explain away certain behaviours
as ‘maladaptive’ (eg. psychopathy, aggression, jealousy,
rape) but evolutionary psychologists try to explain them in
terms of their possible adaptive benefits.
Cautionary Note.
 Not all behaviours are ‘adaptive:
 An adaptation represents a trade-off between different
survival and reproductive needs (e.g having a large body).
 The environment may change more rapidly than the organism
can evolve.
 An adaptation is not always adaptive in every circumstance
(e.g. choking).
 Not all features are adaptive (e.g. belly buttons).
 Gould (1991) cautioned about the use of 'just-so' stories.
 Features that may once have been adaptive for one function
may have changed over time to serve a different function exaptations (e.g. feathers).
 Other features may look like adaptations but in fact aresimply
design constraints (spandrels).
The Role of the Environment.
 Buss et al., (1998) pointed out that the environment can
also play a significant role:
 Interactions
with
environmental
features
during
development are critical for normal development.
 Input during development may be required in order to
activate certain adaptive features (e.g. experience of
sexual relationships and jealousy).
 Developmental events may channel individuals into one of
several different paths (e.g. parenting style).
 Environmental events may disrupt the emergence of an
adaptation.
What Is Evolutionary Psychology?
 Evolutionary psychology is the application of Darwinian
principles to the understanding of human nature.
 Cosmides & Tooby (1992) argued that the evolved cognitive
architecture of the human mind contains unconscious
universal content-specific mechanisms.
 These are referred to as ‘Darwinian algorithms’. Thus for
certain things (i.e. social exchange, parenting, mate
selection preferences, food avoidance, helping kin, etc) we
possess a single universal human culture.
 “Human minds, human behaviour, human artefacts, and
human culture are all biological phenomena.…” (Tooby &
Cosmides, 1992).
 We may thus possess a ‘universal human mental content’.
A Modular Mind?
 There are of course cross-cultural differences.
 Evolutionary psychology predicts that the evolved cognitive
mechanisms (modules) should be context-dependent, as
differential inputs (perhaps provided by different
environments) should evoke different representational and
behavioural outputs.
 For example, while fashion and body adornment vary
markedly between societies, cultural definitions of beauty
remain universal.
 These modules have been generated by evolutionary
processes throughout our history,
 However, it is assumed that they developed mainly during
the Pleistocene (2mya- 10,000ya) when our ancestors lived
in small kin-based, hunter-gatherer societies.
The EEA.
 The period during the Pleistocene during which our
cognitive modules developed is called the ‘Environment of
Evolutionary Adaptedness’ or EEA.
 According to Badcock (2000) the EEA probably consisted of:
 Hunter/gather and/or scavenging subsistence.
 Nomadic or semi-nomadic existence.
 Low population density.
 Small kin-based groupings.
 Simple technology.
 High infant mortality and low life expectancy.
 Vulnerability to the natural environment (predators,
disease etc).
 Few lifestyle options.
Impact on Modern Life.
 Our species has developed psychological mechanisms (and
later culture) to solve a series of adaptive problems related to
a hunter-gatherer lifestyle.
 Such adaptations are not necessarily adaptive to modern
humans, e.g. a preference for foods rich in calories.
 However, Irons (1998) criticised the conception of the EEA as
it creates a false picture of stasis in human evolutionary
history.
 Different populations may have led very different lives
depending on their environments.
 Also certain behavioural features can evolve in quite a short
space of time, e.g. lactose intolerance, so we may be more
adapted to our modern environment than we think.
 Tooby & 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.
Assumptions Underlying
Evolutionary Psychology.
 According to Rossano (2003) Evolutionary Psychology makes
several assumptions:
 1. Proximate versus ultimate explanations: Proximate
explanations explain the ‘here and now’ while ultimate
explanations attempt to explain ‘why’.
 Evolutionary psychology tries to address ultimate causes
while the SSSM only deals with proximate triggers.
 E.g, in all human cultures, males prefer to mate with females
younger then themselves, and females prefer to mate with
males who have access to resources.
 These are proximate preferences for youth and wealth.
 The ultimate cause is that a male who opts to mate with a
younger female, and a female who opts to mate with more
resources will enhance their reproductive fitness.
2. Domain Specificity?
 The more important the adaptive problem, the more
intensely natural selection will improve and specialise the
mechanism for solving it.
 In this way Darwinian algorithms become 'domain specific'
they are designed to solve specific rather than general
problems.
 E.g., vervet monkeys have evolved cognitive mechanisms
that produce and respond to a different alarm call for
different predators (Cheney & Seyfarth, 1990).
 A single, general-purpose alarm call and response system
would be inefficient and would not be selected for.
 The human mind thus includes many functionally distinct
adaptive specialisation's that are domain specific.
 Cosmides has compared the mind to a Swiss army knife.
Example:
Algorithms For Social Exchange.
 Social exchange behaviour is both universal and highly
elaborated in present human cultures.
 It must have been a very important feature of our
evolutionary history:
 Trading tools.
 Sharing food.
 Making and swapping alliances.
 Soliciting help when faced by aggression.
 Cooperation in hunting.
 Gaining sexual access to mates.
 Sharing information about resources.
 Sharing social information.
 Our nearest relatives (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.
 The SSSM argues that we learn such abilities through the
general purpose process of cultural transmission.
Therefore, the logic that underpins such behaviour should
also be generalised.
 Evolutionary psychologists instead argue that we should
have developed specialised cognitive mechanisms for
spotting those who cheat in such exchange situations.
 Such skills will not generalise – they are ‘domain-specific’.
Human Social Exchanges.
 Social exchanges can be viewed in terms of formal logic.
 If the SSSM model is correct we should be equally skilled at
all types of formal logic.
 The ‘Wason selection task’ (Wason, 1966) is a measure of
conditional hypotheses of the form:
 ‘If P then Q’, the logically correct response is therefore ‘ P
and not-Q’.
 In a typical paradigm, < 25% of college students choose the
correct solutions.
 Most pick P but many wrongly select Q instead of not-Q.
The ‘Wason Task’
 Indicate only the card(s) you definitely need to turn over to
see if the documents of any of these people violate the
following rule.
 ‘If a student is rated ‘D’, then their documents must be
marked with a ‘3’.
D
F
3
Correct answer: D & 7 (P and not-Q).
Performance is poor on this version
7
Social Contract Versions of the
Wason Task
 Cosmides (1985) argued that individuals will be able to
detect violations of conditional rules when such rules
represent cheating on a social contract.
 When the same problem is represented as a social decision
(involving the spotting of cheaters – e.g the ‘drinking-age
problem’), around 75% choose the correct solutions.
 This indicates that we do not possess general purpose
reasoning mechanisms but ones highly specialised for
reasoning about social contracts.
 In many subsequent studies, Cosmides and colleagues have
shown that performance is always as predicted by
evolutionary theory and not as predicted by other social
theories.
Supporting Evidence.
 Mealey et al., (1996) asked students to rate the
attractiveness of a set of male photos.
 Each was presented with a fictional description giving
information on their character history (history of cheating,
irrelevant information or history of trustworthiness).
 One week later the same participants showed preferential
recognition for those faces that had been described as
'cheater's.
 Stone et al., (2002) reported the case of a patient who had
suffered extensive brain damage.
 While he performed normally on Wason-type logic
problems, when the problem involved the violation of a
social contract he was impaired.
 This provides neurological evidence that reasoning about
social exchange can be selectively impaired.
Can We Judge a Book by it’s Cover?
 More interestingly, Yamagishi et al., (2003)
identified people who either cooperated or
cheated on a game.
 They then showed their pictures to participants
who had no knowledge of their honesty.
 When asked to recognise the pictures amongst
other (non-seen pictures) the pictures of
cheaters were recognised significantly better.
 he authors argued that cheaters may actually
look different to non-cheaters and people may be
able to pick up on such subtle facial cues.
3. Interactionism.
 Critics often state that evolutionary psychologists are
'deterministic', i.e. they ignore the role of the environment
in shaping human behaviour.
 This is not so, a key assumption underlying evolutionary
psychology is that behaviour is created by geneenvironment interactions.
 E.g. environmental feedback concerning our own mate
value (beautiful or ugly) will then influence our mate
strategies.
 A handsome male may be able to pursue many short-term
matings while a less attractive male may opt for loyalty to a
single mate.
 Both strategies could have genetic roots but the
environment influences their subsequent expression
(Rossano, 2003).
4. The Unconscious Mind.
 The motives which drive our behaviours are not accessible
to conscious awareness.
 lcock (1993) pointed that individuals do not need to be
aware of the ultimate reasons for their activities.
 Cognitive decision-making processes were shaped by
natural selection to enhance reproductive fitness, not
provide us with the capacity to monitor the fitness
consequences of each and every action we take.
 We enjoy sweet foods, become attracted to someone, gain
pleasure from achievement, co-operate and compete, learn
a language etc because we possess physiological and
psychological 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.