evolutionary perspectives

social organisation

how animals interact with and space themselves in relation to other individuals of the same species. both in quantity and quality of relationships

variation

solitary to social. loose aggression to close-knit, highly organised groups

why are humans social beings

group living benefits individuals, so that behaviours which facilitate group living are favoured

Darwin’s theory

evolutionary change through natural selection.

• continual competition between individuals in a population for resources

• some individuals contribute more offspring to the next generation than others

• provided that offspring resemble parents (i.e. physical and behavioural traits are heritable), the traits of individuals that leave more offspring than average will increase in freq over time

  • the contribution of an individual to the gene pool in the next generation is its evolutionary fitness

• this produces evolutionary change

benefits of group living

• lowers probability of being killed by predators

• facilitates finding and capturing food

• improves competitive ability

• improves success at rearing own young

costs of group living

• increased chances of being detected by predators

• higher risk of parasitism

• resources have to be shared with other group member

• increases risk of reproductive suppression

inclusive fitness

the total fitness that an individual gains by breeding itself and helping close relatives to breed

kin selection

the process by which characteristics are favoured due to their beneficial effects on the survival of close relatives

mathematics of altruism

Hamilton’s rule → defines the conditions under which we would expect genes causing an increase in altruistic behaviour to spread

recipient benefit / donor cost > 1 / relatedness coefficient

relatedness coefficients

• mother-child = 0.5

• full siblings = 0.5

• nieces/nephews = 0.25

reciprocal altruism

defined by Trivers. provided the benefit of an altruistic act to the recipient in greater than the cost to the donor, then as long as the help is reciprocated at a later date, both ppt gain

communication

basis for social behaviour. animals exchange specially adapted signals (e.g. vocal, visual, olfactory) to mediate their relationships with others. this sort of interaction facilitates and underpins social behaviour

purpose of communication

• transmit information

• social recognition

• advertising resources

• assessing rivals

emotional communication

emphasised by Darwin. there are apparent similarities in facial expression used in similar behavioural contexts in some primates and humans

what affects mating system

• system of parental case

• extent of defensibility of females

  • do males defend females or vice versa

sexual selection

process by which secondary sexual traits become more elaborated because they increase the owners ability to gain mates

intra-sexual competition

between members of the same sex for a mate. e.g. direct combat

inter-sexual choice

by members of one sex for a mate of the opposite sex. good genes theory, attractive sons theory

sexual dimorphism

males are usually larger, more highly developed weaponry, extravagant displays, but not always

sexual displays

bring sexes together for mating and influence outcome of:

• intra-sexual competition

• inter-sexual choice

information is transferred via signals (and more static cues) that may be visual, acoustic or olfactory (chemical, pheromonal)

resource holding potential

individuals wouldn’t fight if this was assessed and would likely lose. this assessment can only be maintained by selection if the displays give a reliable indication of fighting ability; if weak individuals are able to imitate displays of strong individuals, there would be selection to detect bluffers and use of the bluffable cue for assessment would be abandoned

human evolutionary psychology

• our behaviour is influenced by biological predispositions and our social environment

• as our environment has changed, psychological traits originally selected for may be of little or no adaptive value now

• human behaviour is uniquely flexible and most aspects of it are under control