Unit of Selection

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Reading 1 –
The Units and Levels of Selection by Samir Okasha (Ch 8, A Companion to Philosophy of Biology)

Traditional Darwinian View –
* Though Darwin treats individual organisms as basic unit of selection, other possibilities can be seen * Lewontin (1970) – Natural Selection will operate on any level that exhibits ‘heritable variation in fitness’. * Hence the question of level seems purely empirical – but is not.

Historically –
* The debate of Levels of Selection can be traced back to Darwin himself – Descent of Man (1871) – tries to explain ‘altruist behaviour’ based on selection at group level. * Weismann has also shown a similar thinking of hierarchical levels of selection. * G. C. Williams in Adaptation and Natural selection (1966) attacked the idea of group selection regarding it to be a weak evolutionary force as compared to individual selection – Pointed out that only a concept of between-group selection can be an evolutionary force * Hamilton – Kin Selection

* Hamilton and Williams – ‘Gene’s eye view’ – Popularised by Dawkins (1976)

The Gene’s Eye View –
* Hamilton – Altruistic behaviour towards related organisms. Relatives share same genes, hence the beneficiary of the act will be carrying same gene as the actor – Kin selection. * Hamilton’s rule – Altruism favoured by selection as long as cost incurred by the altruist is offset by sufficient amount of benefit to a related organism. bc>1r [ c – cost incurred, b – benefit enjoyed, r – relatedness] * Dawkins – Selfish gene (1976) – Organisms are mere epiphenomena of Evolution; real competition is at gene level - Gene’s Eye view. * Hence (for example) Altruism takes place based on the fact that the net effect of the trait (Altruism) leads to increase in frequency of underlying gene. * Since gene is the real unit of selection other levels of selection are incompatible with it, and hence a fallacy.

A Change of Mind –
* Dawkins and Hull later have maintained that pitching gene against group (or organism, at that) is a categorical mistake. * Replicator/Interactor distinction.
* Hence group v/s individual is an empirical, while gene v/s individual or gene v/s group is not, as they are not similar entities – as genes are replicators, while individuals/groups are interactors. * Natural Selection a two stage process. And Gene’s eye view is a heuristic, available for any level of interactor selection

Criticism –
* Intra-genomic and Junk DNA do not fit nicely into this picture. * Sober and Wilson – Gene is sometimes the unit of selection in the sense similar to individuals – if genes differ in fitness, then genic selection takes place. * But then we must draw a distinction between process of genic selection and gene’s eye view (Okasha 2004a, 2006) * This would mean categorising genic selection with individual/kin/group selection, while keeping gene’s eye view as a heuristic to explain underlying frequency change of genes due to the higher levels of selection. * Dawkins and Williams confused between inheritance and units/levels of selection.

Group and Kin Selection –
* Williams and Maynard Smith criticised group selection on following lines – * Weak evolutionary force compared to individual selection. * Turnover of group slower.
* Altruism can be explained by Kin selection or evolutionary game theory. * Implausible and Superfluous.
* Sober and Wilson have challenged this –
* Group selection is a potential evolutionary force.
* Early Mathematical models of Group selection relied on unrealistic and maximally unfavourable assumptions. * Kin selection and game theory no alternatives at all, just versions of Group selection presented in formal framework. * Opposition – Kin selection can take place within a single population with no isolated population unlike traditional multi-group selection. * Sober and Wilson’s reply – Relevance of the Group...
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