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’.

FD 3 7

Correct answer: D & 7 (P and not-Q).

Performance is poor on this version

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 gene-environment 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.