L15- 'New' Group Selection Theory

Old group selection:

  • idea by VC Wynne-Edwards

  • observed that individual fecundity was lower at high population densities→ density dependance through competition

    • believed it was due to reproductive self-restraint to avoid over-exploitation of resources so the group could survive

  • ideas were demolished by George Williams and Richard Dawkins

  • know that group selection is unlikely as any behaviour designed to increase success of conspecifics is vulnerable to exploitation by selfish individuals

Model:

  • in theory→ can work if selfish groups die out faster than cooperative groups

    • if selection is operating most strongly at the group level:

  • but know that selection acts more on individuals than groups

  • for group selection to work, groups have to be isolated and individuals cannot move→ biologically unlikely

→ these models do not have much biological realism

New group selection:

  • advocated by 4 main people:

  • idea that we can see a hierarchy of multilevel selection:

Model:

  • populations are divided into trait groups or demes (share similar traits)

  • groups can mix together before splitting into new groups

  • cooperative groups are expected to contribute more to new groups→ are more successful than selfish groups

  • new groups tend to share traits→ mainly cooperators or mainly selfish

→ cooperative traits spread when between group selection (how much groups outcompete other groups to contribute to new groups) is stronger than within group selection

Predictions of model:

  • cooperation is favoured by:

    • increasing group benefits→ cooperative groups are more likely to contribute to new generation

    • reducing individual cost of cooperating

    • reducing within-group variance in cooperative behaviour, relative to between-group variance→ the more like individuals cluster together increase the probability of cooperation being expressed

  • 3 conditions link to Hamilton’s rule:

    • increasing group benefits→ high B

    • reducing individual cost of cooperating→ low C

    • reducing within-group variance in cooperative behaviour, relative to between-group variance→ high r

→ condition under which cooperation evolves in the new group selection models is mathematically equivalent to Hamilton’s rule for the evolution of altruism

Are these two equal then? NO:

  • inclusive fitness theory→ tells us the quantity natural selection seeks to maximised under all conditions, expect an individual to be selected based on how its behaviour contributes to its inclusive fitness

  • new group selection→ tells us the certain conditions that group selection will operate (isolation), does not look at the maximum group fitness that will be selected for

  • is causing conflict in literature

  • study→

    • looked for models of evolution of altruism in the literature→ analysed 89 of these that were significantly different from each other

      • 46 concluded kin selection was driver of selection

      • 43 argued there was another route

        • all alternative routes were reinventing kinship→ high relatedness favours altruism

Do we see group selection in natural systems?→ empirical studies:

e.g. Social Spider-

  • live in large groups, capture prey collectively, composition of bold and shy spiders, massive webs

  • conditions matching predictions for group selection→

    • colonies frequently became extinct

    • had limited dispersals between colonies

    • colonies had a mix of docile and aggressive phenotypes

  • manipulated compositions of groups, observed what happened over time:

    • group level traits persisted, combinations tended to be more successful in certain habitats than others

  • HOWEVER fabricated data→ was scientific fraud

→ there is no good evidence of group selection in natural systems

  • selection mainly occurs at the level of individuals or genes

Conclusions-

  • Theoretical work to ‘revive’ group selection continue…

  • Group selection models that work and inclusive fitness models are mathematically equivalent

  • Inclusive fitness theory is far more useful because it gives us the quantity that natural selection maximises

  • Advocates of group selection often appear to have an agenda of denial e.g. Nowak et al. (2010): “empirical evidence [for IFT] is meagre”

  • No empirical evidence…