Altruism Flashcards
What is altruism?
Behaviours that increase others’ survival chances at a cost to your own
Examples of non-human animal altruism
Wilkinson, 1990
- Vampire bats regurgitate blood and feed hungry bats
Sherman, 1977
- Ground squirrels give alarm calls, drawing predators’ attention to themselves while warning others of it’s presence
Naked mole rats are eusocial - like bees! ‘Queen’ dominant female is the only one who breed. Other females are sterile workers
How could altruism come about?
Individual fitness
- no. of own offspring
Gene’s eye view
- no. copies of genes make it to next generation (includes other family members)
Genetic overlap
Genes shared with relatives
- child-parent r = 50%
- siblings r = 50%
- grandchild-grandparent r = 25%
- aunt/uncle-neice/nephew r = 25%
- cousins r = 12.5%
r = coefficient of relatedness
Inclusive fitness
Sum of direct fitness & indirect fitness
direct fitness = genes passed on by you to your offspring
indirect fitness = genes passed on by aid to relatives
Kin selection hypothesis –> helping relatives survive and reproduce helps spread your shared genes
Evidence for kin selection hypothesis
Hamilton’s rule
- genes for altruism will spread if r x B > C
- **r = coefficient of relatedness
- B = benefit to receiver
- C = cost to giver
Wilkinson, 1990
- Vampire bats more likely to share food with relatives
Sherman, 1977
- Ground squirrels only signal danger when there are many relatives present
Kin selection in humans
Barrett et al., 2002
- food sharing more common amongst close relatives
- political alliances between kin are more stable
- passing of wealth to lineal descendants more common than giving to unrelated others
- close relative preferentially sought in times of need & such help is less likely to be reciprocal
- relative typically receive more expensive presents
Burnstein et al., 1994
- House is burning - who do you save?
- 7-yr-old female cousin
- 75-yr-old grandmother
- 21-yr-old female acquaintance
- simple favours - favour old, sick, poor
- life or death - favour closer kin, young, healthy, pre-menopausal
Kin identification
Platek et al., 2004
- facial warping of child toward or away from own appearance
- who do you adopt?
- spend more time with?
- punish most?
- resent paying child support for?
- self morphs selected more often, especially by males for positive traits
DeBruine, 2002
- play trust games with ‘opponent’ - face resembles self or is very dissimilar
- more trusting actions towards self-resemblance faces
- adaptive response to kin
Evidence against kin selection
de Waal & Luttrell, 1999
- Chimpanzees help unrelated others e.g. when they are injured
Wilkinson, 1990
- Vampire bats often feed non-relatives
People giving blood
People helping animals
Reciprocal altruism
Trivers, 1971
- natural or sexual selection could create altruism, provided
- B > C
- recognition and memory of individuals and their actions to reciprocate and spot cheaters
- possibility of repeated interactions
Models of reciprocal altruism
Prisoner’s dilemma
Best personal choice is to snitch
Should work together, both stay quiet to get best possible 2-way outcome
Axelrod, 1981
- devised set of strategies for repeated interactions. Best was…
- tit-for-tat = whatever you do, I’ll do in return on the next turn
- evolutionarily stabe - constant co-operation with instant punishment = mutual benefit
The Ultimatum game
Proposer has money, offers a split.
If responder accepts, each gets proposed payoff.
If responder rejects, each gets nothing.
Henrich et al., 2005
- People are willing to go without to punish people who give low offers
- costly punishment allows complex societies to grow - cheaters are punished early, collboration spurs growth
Sigmund et al., 2002
- developed from small living groups where cheating more than once would be impossible - we expect others to remember our actions
Gene-culture co-evolution of altruism
Fehr & Fischbacher (2003)
- genes - kin selection
- culture - future encounters, individual reputation formation
Reputation formation
Milinski et al., 2002
- reputations of helping previously in public goods interactions (multiple people) determin later donor decisions
- donors punish recipients who defected in public goods game by being less likely to help in bilateral (1-1) interactions - increases cooperation in future public goods rounds
Limits of human altruism
Fehr & Fischbacher (2003)
- Reciprocal individuals reward & punish in anon one-shot interactions but increase reward/punishment in repeated interactions if reputation is at stake
- Altruism-selfishness interaction
- altruism in one-shot interactions
- selfishness of reputation building is possible
Isaac & Walker, 1988
- Frequency of altruistic acts decreases as costs increase
- Public goods games, dictator games
