Thursday 20th September - Cooperation and Altruism COPY Flashcards
First, a couple important definitions
• Cooperative behaviour: ?
• Altruism: ?
• Cooperative behaviour: A mutually beneficial interaction between individuals.
• Altruism: A behaviour resulting in the increased fitness of another individual that incurs a cost to the individual performing the behaviour.
The puzzle of Altruism
Two fundamental assumptions of models of behaviour based on population genetics:
- Default patterns of behaviour are heritable, i.e., genetically fixed.
- Only genes controlling adaptations that favour survival or lifetime reproductive success of individuals can pass scrutiny by natural selection.
But various degrees of sociality, cooperation and altruism do exist.
- There are heritable behaviours that advance lifetime reproductive success of others at cost of own reproductive success.
- Seems intuitive if natural selection works for the “good of the species” – but it doesn’t!
Degrees of sociality
No altruism = ?
With altruism = ?
• All animals are socially aware, but degree of sociality determined by habitat, distribution of resources, genetic relationships and the behaviour of others.
No altruism
– Solitary or pairs
– Aggregations, e.g., at waterhole
With altruism
– Pack (co-operative hunting)
– Society (with division of labour)
Important questions to think about
In evaluating various forms of cooperative behaviour, ask:
1. Who benefits? – if one partner doesn’t benefit, it is not cooperation but manipulation (commensalism or parasitism)
2. How? – As an individual? If not, the group? – Or the genes it/they carry?
3. When? – Now or in the future? – Self or offspring?
Forms of cooperative behaviour
These are not mutually exclusive: mutualism overlaps with reciprocal altruism in unrelated individuals, and with kin selection in related individuals.
What is Mutualism?
Mutual benefit of individuals
– requires common interests, i.e. no competition
– Especially, but not only, amongst relatives
– Also within and among species
A) Explain ‘Within’ species and ‘Between’ species mutualism and give an example of each.
Within..
- grooming important to strengthen social bonds in e.g., zebras, many primates.
- pack hunting, assistance in agonistic interactions (Japanese macaques)
- shared vigilance increases average feeding rate of group
Between…
- cleaners (fish, birds, crabs, etc)
- ants and aphids
- mongooses and hornbills Mutual benefit are easy to assume…
“Obvious” explanations aren’t always correct
Classic example: Oxpeckers pick ticks off African game animals
- Adaptive advantage to a giraffe or zebra of tolerating oxpeckers usually assumed to be that oxpeckers remove ticks
- Animals with oxpeckers should have fewer ticks - but not so!
Another explanation Mean
of wounds per ox • Red-billed Oxpeckers also peck at open wounds and probe the animals’ ears for ear wax.
- Cattle protected from oxpeckers do not have any more ticks than cattle exposed to them…
- But they do have fewer open wounds and more earwax
Kin Selection
• Benefits of altruism can be ______ & ________?
– This means that benefits will be rewarded in passing on of genetic material.
• If an individual can produce more offspring by helping a sibling, after penalization by genetic relatedness, then this will be favoured by kin selection.
– B = Benefit (extra offspring the relative produces due to altruistic act)
– R = coefficient of relatedness (relatedness of altruistic individual to relative)
– C = Cost (# of offspring individual doesn’t produce due to altruistic act)
• Hamilton’s rule:
Altruism can evolve when ? x ? > ?
Direct (helping own offspring).
and
Indirect (helping family members = kin selection).
• Hamilton’s rule: Altruism can evolve when B x r > C
Quantifying ‘indirect’ fitness
Example: A bird can raise 2 offspring without help, but could raise 5 with help from sister. The sister could only raise 1 on her own. B = 4, C = 1, r = 0.5 (for full siblings).
• Apply to B x r > C: So, is 4 x 0.5 >1? YES, Hamilton’s rule predicts that the sister will help (increases her total contribution to the gene pool)
Kin Recognition
Not the same as kin selection, but a precondition of it – why?
• Because kin selection requires that altruism be confined to relatives
• Recognition rules are mostly simple, what are they
– By location
- all in my nest are kin
• But this rule can be exploited (e.g., cuckoos; parents ignore own chick outside nest)
– By association
- all I grew up with are kin
• humans almost never marry adopted siblings
– By similarity
- all like me are kin = phenotype matching (e.g. smell, colour)
So does altruism vary with (perception of) relatedness?
- Reciprocal altruism
• Definition: one gains now, the other later.
– contrast to mutualism = both gain at the same time.
• Partners unrelated
– If related, kin selection operates.
– Both processes act together in mixed groups.
• Requires ability to
– Recognise individuals most often encountered.
• Not just relatives, so recognition not genetic.
– Remember and exchange benefits.
• Found mainly in permanently sociable groups of mammals and birds where:
– Sufficient capacity for learning and memory
– Personal survival depends on mutual aid
The “problem” with reciprocal altruism
• Question: How to avoid exploitation by cheats who don’t reciprocate?
– E.g., a hunter who demands a share of others’ meat but doesn’t help or share own.
• Answer: “keep score” and refuse aid to cheats
– Essential, since fitness payoff depends only on whether favour is returned
• requires ability to choose to cooperate or not
– but how to decide?
• Enter game theory
– The study of social decisions
Consequences of choice
• If only one type of game possible = no choice
– most predation is a win-lose game: e.g., lions adapted to hunt; can’t eat grass instead.
- Dilemma arises if players can choose whether to play by scoring off each other or by cooperating to score off 3rd party (could be any kind of resource).
- If choices have to be made simultaneously and without communication,
- AND if the payoff for cooperation is larger than for random play, then game becomes a Prisoner’s Dilemma
– A range of possible payoffs can be calculated
Classic Prisoner’s Dilemma
From match to deal: repeat games
- One-off encounters are a match of wits
- If the same players meet repeatedly (game is iterated) then the outcome changes
– previous experience allows prediction of what opponent is likely to do next
In Iterated Prisoner’s Dilemma (IPD)
Cooperation becomes less risky; eventually becomes the best strategy
• Most social animals interact with the same individuals daily, so IPD leads to cooperation between unrelated group members = reciprocal altruism
If they only meet once they’re more likely to default to this option but if they are repeatedly meeting each other again and again they are more likely to come to this mutual arrangement.
Essentially the conditions that favour this cooperative interaction amongst non relatives depends on whether or not they know how many times they will meet each other.
Also depends on the animals ability to retaliate if they do get cheated on, also depends on an element of forgiveness..
(if they do keep cheating on each other and at one point one of them decides to break the vicious cycle and just help, the other animal also needs to forgive the animal and start helping again as well which blossoms into a beautiful relationship.
