Evolutionary Explanations of Human Behaviour

Evolutionary Explanations of Human Behaviour

Objectives • Assess prior knowledge • Define Evolution • Define Evolutionary Psychology

What is Evolutionary Psychology? Read the article on page 3 of your resource pack. Pick out 5 key points from the article and write them on a post-it!

Darwin Natural Selection Evolution Genetic Appear Adaptive

Mastery Test How much do you already know? Complete the multi-choice test on page 2 on paper Work on your own in SILENCE!!! 2min Go! STOP

Marking the Test • Swap papers! • Mark the answers as I read them out • How did you do? • You will complete this again at the end of the topic – aim to improve!

Extension Tasks • Complete the definitions and the picture of the model on page 1 of your workbook • Create a poster about the four parts of Modern Darwinism

Parental Investment Sexual Selection Human Reproductive Behaviour

Objectives • State the nature of sexual selection • Evaluate the nature of sexual selection • State the forms of sexual selection • Evaluate the forms of sexual selection • State the consequences of sexual selection • Evaluate the consequences of sexual selection

My ideal partner! • Take a piece of plain paper. • Draw the head of a person. • Fold it over and pass left. • Draw the body and arms of a person • Fold it over and pass it left • Draw the legs and feet of a person • Fold it over and pass it left

Key Definition! • EEA (Environment of Evolutionary Adaptation) • This is the environment to which a species is adapted and the set of selection pressures that operated at this time. • Generally regarded as the time when our ancestors were hunter-gatherers on the African savannah.

Nature of sexual selection – Gender Specific • Characteristics to promote reproductive success • Men – young healthy females • Women – resource investment • Female – more choosy (intersexual competition) • Male – compete with each other (intrasexual competition)

Evaluation • Buss (1989) study of 37 cultures. • Men – choose on fecundity • Women – choose on resource potential • Scheib (1994) – sperm donor choice study supported Buss’ findings

Evaluation • Bereczkei (1997) – females advertised for family-orientated men • Female financial independence • Homosexual relationships – no reproductive potential. • Dunbar (1995a) Homosexual adverts also advertise resources – despite having no reproductive potential

Nature of Sexual SelectionOrigins of Mate Preferences • Preference for one mate over another • Links to problem of appropriate mate choice in EEA • Mating biased in favour of individuals with certain characteristics • Genetic quality of mate determines genetic quality of offspring!

Evaluation • Human behaviour influenced by selective pressure in EEA is not universally accepted. • Continuing evolution • Why so affected by one environment and not another?

Forms of sexual selection – Selection for Indicators • Indicators reveal traits that can be passed on. • Show information about mate survival • Tend to be condition dependent – healthier = bigger – or revealing – make better use of indicators, e.g. better groomed • Pre-programming

Evaluation • Indicators can be faked! E.g. female lips • Handicaps only reliable indicator (Zahavi 1975) • Facial symmetry.

Forms of sexual selection Selection for sperm competition • Sperm is stored • Size matters! • Male humans have medium-sized testicles by primate standards. • Ancestral males mildly competitive – females must have had multiple partners (Baker & Bellis 1995)

Evaluation • Humans are by nature more promiscuous than monogamous • 9% misattributed fatherhood (Baker & Bellis) • Majority of people do know who their father is • Majority not adulterous

Competition Activity • Complete the human intra-sexual competition activity. • Be prepared to share your opinions

Consequences of sexual selectionPhysical Characteristics • Dimorphism (physical differences between the sexes) is linked to female mate choice Martin et al. (1994) • Size difference = polygynous mating system (one male, many females) • More sexual competition between males.

Consequences of sexual selectionPhysical Characteristics • Facial Characteristics • Neotenous (child-like) more attractive (Perrett et al 1994) • Strong testosterone linked features • Facial symmetry (Thornhill & Gangstad 1993)

Sexual selection & Human mental evolution • Physical and mental • Neophilia (love of novelty) • Favour the creative (Miller 1998)

Extension Task • Complete the task on Fisher’s hypothesis.

Objectives • State & evaluate parental investment theory • Compare and contrast the differences between maternal and paternal investment and evaluate these

Fisher’s Hypothesis • What did we find out?

Key Definition • Parental Investment – any investment by a parent in one of his or her offspring that increases the chance that the offspring will survive at the expense of the parent’s ability to invest in any other offspring (alive or yet to be born) (Trivers 1972)

Parental Investment Theory • Trivers (1972) • Males and females do not invest equally • Gametes

Evaluation • Plausible explanation (Buss 1998) • Men gain from polygyny. Females from monogamy. • Polygyny common prior to Western influence. (Smith 1984) • Reproduction rates are low among wealthy people. • Contraception • Socially enforced monogamy

Maternal vs. Paternal

Evaluation • Females want male providers because of infant dependency • Female want good quality offspring. • Mistaken paternity supports this.

Cuckoldry • Self-protection against cuckoldry • Considerable investment = need for fidelity (Miller 1998) • Care not misdirected

Paternal love • Read the article on paternal love in the resource pack • Pick out 5 key points and transfer to post-it notes • Be prepared to share

Sexual Jealousy • Different adaptive problems for males and females • Males – incorrect investment • Females – diversion of resources • Sexual jealousy a solution (Buss 1995) • Men – jealous of sexual act • Women – jealous of shift in emotional focus

Evaluation • Buss et al. (1992) male concerned with sexual fidelity, female concerned with emotional fidelity. • Galvanic skin responses • Veil • Changes in sexual morals • Surplus of men means marital life is more stable (Hill & Hurtado 1996)

Evaluation • Dunbar (1995b) Joint parental investment is desirable because of high cost of successful reproduction. • Males restrict reproductive activity and invest more in each offspring. • Greater male selectivity means female attractiveness is important compared to non-human animals.

Sexual Jealousy • Complete the activity on sexual jealousy in the activity pack. • Be prepared to share your answers

Extension Activity • Complete the activity on polygyny and polyandry • Ensure it is complete by next lesson.

Objectives • State the main ideas about parent-offspring conflict • Evaluate the main ideas about parent-offspring conflict

Polygyny & Polyandry • What did we find out?

Parent-offspring conflict • Trivers (1994) • Parents will be in conflict about weaning, parents will want to wean earlier than the child • Parents will encourage children to value siblings more than they are naturally inclined to • Parents will punish conflict and reward co-operation.

Sibling Rivalry • Individual offspring • Fair share • Maximise fitness • Sibling rivalry for attention and resources

Evaluation • Lalumiere et al. (1996) Different developmental paths • Harris (1999) Peer socialisation

Age related parent-offspring conflict • Begins at conception (Buss 1999) • Pre-eclampsia • Sibling investment • Transfer of investment

Evolutionary Explanations of Human Behaviour