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