Social Behaviour

Social Behaviour

1. Kin Altruism/Inclusive Fitness

   • Hamilton's rule
     • rb > c
       • r - average coefficient of relatedness between actor and recipients
       • b - the sum of the fitness benefits to all individuals affected by the behaviour
       • c - the fitness cost to the individual performing the behaviour
     • Animals = inclusive fitness maximisers
     • Direct fitness - genes which are passed on to the next generation via an individual's offspring
     • Indirect fitness - genes passed on via aid to other kin
     • Animals provide care to others
       • Share genes with them by common descent
       • Amount of care given will increase as does proportion of genes shared
     • Show altruism to those that share the same gene by common descent - favoured by natural selection
       • Kin selection
   • Burnstein et al. (1994) - most likely to give aid to relatives
   • Stewart-Williams (2007) - low-cost aid - give aid to friends as much as kin. High-cost aid - kin favoured
   • Altruism limited to kin and closer kinship facilitates more costly altruism
   • Criticism
     • Sahlin (1976)
       • Hunter-gatherers - incapable of calculating r = unable to act appropriately
       • Adoption practices of hunter-gatherer societies - do not predict altruism
         • Coefficient of relatedness typically reported between adopters and adoptees ?
         • EEA - adaptive sense to adopt young individuals - may have been relative of some degree
       • Criticism of criticism
         • Not necessary for an organism to have insight into either how or why it does something. It is merely sufficient that it generally behaves in ways that are likely to increase its inclusive fitness

2. Parental Investment and family life (Trivers, 1972)

   • R-selection - production of vast numbers of offspring at little cost per individual
   • K-selection - production of very few offspring at great cost per individual
   • Female of long-lived internally fertilised species with lengthy period of development - invest greatly in offspring
   • Humans - family = disposition to mate and disposition to favour kin
     • Not just feeding - protection and teaching
   • Parental manipulation - parents tend to teach their children to behave benevolently towards each other
     • Parents' genes that benefit

3. Parent-Offspring Conflict (Trivers, 1974)

   • K-selected species - invest heavily in offspring
   • Can become pregnant - female can breed again - invest in another offspring
   • Time to invest comes faster to mother than it does to first offspring
   • Sibling rivalry - investment drawn away from first offspring
   • Dunbar and Barrett (1994) - tantrums used by wide variety of infant animals to increase maternal investment
     • Conflict reaches peak at time of weaning
   • Cost/benefit asymmetry between mother and daughter - mother doesn't want daughter to reproduce so she can help raise mother's offspring
     • Fades when mother passes reproductive age
   • Flinn (1989; 2011) - no girl of reproductive age became pregnant until mother's last-born child was at least 4
     • Reproduction suppression mechanism
     • Mother can still reproduce - doesn't matter if daughter or mum reproduces
     • Suits both parties
   • Household agnostic encounters more likely to be initiated by the mother
   • Should be fewer of these encounters involving teenage sons than daughter