COMPARATIVE PSYCHOLOGY Evolutionary explanations of human behaviour

1. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour Four important points to recognize in relation to evolution: Evolution is a fact. Living species have changed or evolved over time. Darwin’s theory of evolution is an attempt to explain the forces that cause such change. Natural selection is the basic process that drives evolution. Any trait that enhances reproduction will be naturally selected.

2. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • THE NATURE OF SEXUAL SELECTION • An important adaptive problem for both sexes is • the selection of a suitable mate. • Certain characteristics lead to lower reproductive success therefore are not selected. • Low in re-productive capacity (e.g. older) is one characteristic. Cont… HUMAN REPRODUCTIVE BEHAVIOUR

3. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • THE NATURE OF SEXUAL SELECTION • Males and females face different adaptive problems when selecting a mate. • Since women have to make a greater investment in their offspring, through gestation and infant care, they are more choosy whom they will mate with. • Males have to compete with each other (intrasexual competition) to be chosen. HUMAN REPRODUCTIVE BEHAVIOUR

4. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • FORMS OF SEXUAL SELECTION • Physical and behavioural indicators reveal traits that could be passed on to offspring (‘good genes’) and information about the chances of the mate surviving to protect and support the offspring (selection for ‘good parents’). • Indicators tend to be ‘Conditional dependent’ - healthier individuals take better care and make better use of the indicators they have (better groomed and better displayed). Cont… HUMAN REPRODUCTIVE BEHAVIOUR

5. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • FORMS OF SEXUAL SELECTION • Human beings are ‘pre – programmed’ to attend to displays of these important indicators, which in turn increases their Willingness to mate. • Male humans have medium – sized testicles by primate standards, suggesting that the norm for ancestral males was to be mildly competitive, so females must have had multiple partners (Bakers and Bellis, 1995). HUMAN REPRODUCTIVE BEHAVIOUR

6. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • CONSEQUENCES OF SEXUAL SELECTION • Dimorphism – physical differences between sexes. • Polygynous mating system – one male and many females. • The moderate size difference between human males and human female suggest that our species evolved under a polygynous mating system, with more intense sexual competition between males than females. Cont… HUMAN REPRODUCTIVE BEHAVIOUR

7. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • CONSEQUENCES OF SEXUAL SELECTION • Females with (child –like) facial features, such as large eyes and small noses are universally considered more attractive (Perrett et al., 1994), as are males faces with testosterone – influenced features such as strong jaws and larger noses (Thornhill and Gangestad, 1993) • Neophilia (the love of novelty) influences mate choice in many species. Creative ‘behavioural courtship displays’ such as jokes, dance, music and art (Muller, 1998). HUMAN REPRODUCTIVE BEHAVIOUR

8. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • SEX DIFFERENCES • Sexual selection occurs as a result of the different levels of parental investment between males and females, as well as between different individual men and females. • In humans, it is the female who biologically invests more than the male. PARENTAL INVESTMENT

9. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • SEX DIFFERENCES • Why do human females invest more than males? • Anisogamy – females invest in producing relatively few, large, long lasting and energy rich gametes (ovum), while men produce many short lived and rapidly renewable gametes (sperm). • Gestation and lactation – females provide more resources by developing the zygote internally for nine months (gestation) and producing milk for offspring nutrition (lactation). PARENTAL INVESTMENT

10. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • SEX DIFFERENCES • Why do human females invest more than males? • Parental certainty – because of anisogamy and internal conception, the females always knows the offspring is hers unlike males (parental guarantee is not certain). • Commitment to resources – because of the previous factors and the helpless nature of babies, females are likely to continue care for the baby due to the already significant investment put in by the mother. PARENTAL INVESTMENT

11. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • SEX DIFFERENCES • Male investment! • Male investment after conception is more uncertain due to lack of parental guarantee. PARENTAL INVESTMENT

12. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • SEX DIFFERENCES • Male investment! • Further male investment depends on [part 1]: [1] the number of females available. [2] a low female – to – male ratio. [3] a high degree of competition from other males. [4] a low appeal to other females (mate choice). All the above points will increase the investment in offspring. PARENTAL INVESTMENT

13. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • SEX DIFFERENCES • Male investment! • Further male investment depends on [part 2]: [1] The likelihood of infant survival. [2] Harsh climate. [3] Many predators. [4] Lack of food and social support. The helpless infants are less likely to survive with only the mother’s care. PARENTAL INVESTMENT