Organisms, Groups and Superorganism

Sex and Death: An Introduction to Philosophy of Biology

8.1 InteractorsIdentifying Interactors – Copidosoma Floridanum Example

8.1 InteractorsIdentifying Interactors – Copidosoma Floridanum Example

8.1 InteractorsIdentifying Interactors – Copidosoma Floridanum Example

8.1 InteractorsIdentifying Interactors – Copidosoma Floridanum Example

8.1 InteractorsIdentifying Interactors – Copidosoma Floridanum Example

8.1 InteractorsIdentifying Interactors – Copidosoma Floridanum Example

Should we think of all the clones as a single interactor or as individuals?

If they are individuals, how can such suicidal behaviour evolve?

8.1 InteractorsHierarchical Conception of Evolution

Organisms are only one level of organization Organized groups may also be relevant to

evolution Main motivation for HCE is that it can explain

the challenge of altruism

8.2 The Challenge of AltruismWhy altruism?

Selection should favour selfish behaviour

Yet many organisms seem to show altruism

8.2 The Challenge of AltruismThree possible explanations

1. Error/imperfect adaption to the environment

2. Altruism is an illusion

3. Selection on the collectives

8.3 Group Selection: Take 1Wynne-Edwards

Reproductive contstraint as central example of altruism

Reproductive constraint evolved through group selection:– Groups that don‘t show reproductive constraint go

extinct and are replaced by groups that do

8.3 Group Selection: Take 1Challenges

Altruism is an Illusion Kin Selection/Inclusive Fitness

– Individiuals can promote the projection of its genes into the future not just by reproducing itself but also by helping close relatives (similar genes) to reproduce

Self sacrifice can be selfish

8.3 Group Selection: Take 1Subversion from Within

Selfish individual in an altruistic group has a higher fitness than an altruistic individual

Individual selection favours egoism Individual selection has shorter generation

time and higher variety than group selection Individual selection should outperform group

selection

8.4 Group Selection: Take 2Trait Groups

Wilson introduced the idea of trait groups

– group of organisms that each feel the influence of the others with respect to some trait

8.4 Group Selection: Take 2Trait Groups as Unit of Selection

Wilson: Trait group is a unit of selection Trait group selection can overpower individual

selection, even though selfish individuals are fitter than altruistic ones in both selfish and altruistic groups (Simpson‘s paradox)

8.4 Group Selection: Take 2Simpson‘s Paradox

Application of Simpson‘s paradox– Fitness(altruist individual) < Fitness(selfish

individual) in both selfish and altruistic groups– Fitness(altrustic groups) > Fitness(selfish groups)– Can lead to Avg. Fitness(altruist) > Avg.

Fitness(egoist) in combined groups– If most altruists are in an altruistic group

8.4 Group Selection: Take 2Wilson‘s Response to Kin Selection

Kin selection is a special case of trait group selection– Genetic relatedness only relevant as it generates

the correlation between having a trait and being in the same group with others having this trait

8.4 Group Selection: Take 2Wilson‘s/Sober‘s Response to Reciprocal Altruism

Reciprocating individuals form a trait group Reciprocal altruism evolves as reciprocating

groups outperform other groups

8.5 Population Structured EvolutionChallenges to group selection: Are Trait Groups really Interactors?

Are trait groups really interactors? Alternative view: Groups are rather part of the

environment (broad individualism) Authors argue that broad individualism and

(trait) group selection are equivalent

8.5 Population Structured EvolutionOne True Story?

Group selection: altruism evolves because altruistic groups are more productive and group selection can outweight individual selection

Broad individualism: altruistic individual is fitter than the 'freeloader' because it is more likely to live in an altruistic group

8.5 Population Structured EvolutionOne True Story cont‘d

Both views recognize importance of groups and that an individual‘s fitness depends both on the character of the group they are a member of as well as its own behaviour

Both views are equivalent formulations of population structured selection.

8.6 Organisms and SuperorganismsSuperorganisms

Organisms are objectively interactors

Some collective individuals are enough like an organism to be a real composite interactor, a 'superorganism'

8.6 Organisms and SuperorganismsDefining/Identifiying Superorganisms

Two suggestions how superorganisms could be identified:– physical cohesion– reproductive fate is irrevocably tied to that of others

However, the nature of superorganisms is not well understood