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Evolution - Coggle Diagram

- - - - Organisms in Social Groups
        
        Many organisms are found in groups
        
        May be close kin or not kin
        
        E.g., Superb fairywren
        
        One nest have multiple males helping out in raising the young of a single female
        
        e.g. Social lizards
        
        In lizards we can see parent-offspring interaction, monogamous pairing, social barriers
      - Why be Social?
        The problem of altruism: Why should organisms help each other?
        
        Kin Selection
        
        Often groups consist of close kin
        
        This helps to gain inclusive fitness
        
        Benefits of Kin Selection
        May be direct or indirect
        
        Direct Benefits
        
        May include food, shelter, protection from predators
        
        Indirect benefits
        
        Genetic benefits to the individual and/or offspring (fitness)
        
        Costs of Kin Selection
        
        Increased visibility to predators
        
        Less food available
        
        Crowded territories
        
        Inclusive Fitness
        
        Benefits to genetic legacy by assisting close kin to increase their fitness according to Hamilton's rule
        
        Hamilton's definition: An individual's direct fitness (reproductive success) plus the direct fitenss of kin, weighted by their relatedness to the individual
        
        Hamilton's rule
        Engage in altruistic behaviour when
        rb > c
        r = relatedness
        b = benefit
        c = cost
        (in units of fitness)
        
        Relatedness
        Usually calculated as 0.5 to the power of the number of generations between two individuals via their most recent common ancestor
        
        e.g. Grandmother and grandchild (2 generations)
        
        relatedness = 0.5 x 0.5 = 0.25
        
        e.g. Two full cousins (2 gens up & 2 gens down)
        
        relatedness = 0.5 x 0.5 x 0.5 x 0.5 = 0.125
        
        This calculation works with diploid organisms without inbreeding
        
        More complicated with Eusocial insects (Hymenoptera: Bees, ants, wasps, sawflies)
        
        haploid males
        
        diploid females
        
        1 more item...
        
        Reciprocital Altruism
        You scratch my back and I'll scratch yours
        
        Reciprocity works when:
        
        Actors are likely to be repaid in the future
        
        More likely to occur in speceis that form stable groups
        
        as actors are more likely to encounter each other through time
        
        Group Selection
        The idea that individuals work together for the 'good of the species'
        
        Originally put forward by Wynne-Edwards (1962) Animal Dispersion in Relation to Social Behaviour
        
        Argument basically destroyed by George C Williams (1966) Adaptation and Natural Selection
        
        Why Group Selection doesn't work
        
        Group-selected behaviours are subject to cheaters
        
        Tragedy of the Commons
        
        The benefit of cheating outweighs the cost to the individual, since the cost is shared by all participants
        
        e.g., Adding 1 more sheep to graze in a common field benefits the herder at the cost of the society's pasture
        
        Group Selection can work
        
        When:
        
        Groups are stable:
        
        Individuals don't switch between groups
        
        Groups give rise to more groups as a result of cooperative behaviours
        
        Group reproduction may mean producing more individuals, dispersing into new environments etc.