Lecture 15- levels of selection Flashcards
what is old group selection?
Reproductive self-restraint to avoid over-exploitation of resources
who came up with old group selection?
VC wynne Edwards
what was the idea of old group selection demolished by?
by the revolution of thought of inclusive fitness theory
- the selfish gene - Richard Dawkins
why are the conditions for old group selection are unlikely to be met in nature?
1)In theory, group selection can work if some groups die out faster than others. But, individuals usually die at a faster rate than groups, so individual selection will be more powerful.
what needs to happen for old group selection to work?
groups must be isolated so that selfish individuals can’t migrate into cooperative groups
under the theory of old group selection would would happen to selfish and cooperative groups?
cooperative groups proliferate and selfish groups would go extinct
3 people that came up with ‘new’ group selection
1) EO Wilson
2) Martin Nowak
3) David Sloan Wilson
describe the basic thinking of new group selection
The basic thinking is that selection doesn’t really work on genes or individuals but also operates at a group level = multi level selection - Wilson argues that to understand selection you have to look across levels
describe the theoretical core argument of new group selection
• Populations are divided into ‘trait groups’ or ‘demes’
• Selection acts for or against cooperative traits within groups
• Groups mix together before splitting into new groups and the next round of selection
- some groups will contribute more to the mixed group because they are cooperative - groups made up of selfish individuals will be less successful and contribute less to pool - intermediate contribution from group composed of selfish and cooperative
•Pool of individuals then organize themselves in separate groups according to the possession of particular traits - cooperators tend to associate themselves with cooperators and selfish with selfish = assortative association according to traits possessed - through time this would result in the spread of cooperation
under new group selection when would cooperative traits spread?
• Cooperative traits spread when between group selection is stronger than within group selection i.e. cooperation can evolve through group selection
in the new group selection model what is cooperation favoured by?
- increasing group benefits (B)
- reducing individual cost (c)
- reducing within-group genetic variance, relative to between-group genetic variance (r)
what are new group selection models mathematically equivalent too?
Hamilton’s rule for the evolution of altruism: rB > C
If new group selection and inclusive fitness models are mathematically equivalent, are they also equally useful?
NO!
- inclusive fitness underpins everything in module
- new group selection theory has low generality
give an example of a species thought to show new group selection in the natural world? (before this study it wasnt thought any did )
social spider - Spiders form groups and cooperate together forming webs and hunting etc
Each web is composed of a mixture of two behavioral types
• Colonies have a mix of docile and aggressive phenotypes which are site-specific and affect reproductive success
describe the study on social spiders
• Artificial colonies of varied mixes of docile/aggressive phenotypes introduced to different sites
• Some introduced to their ‘native’ site, others to ‘foreign’ site
• Monitored after two generations
- Found outcomes to match expected mix of social phenotypes
- Colonies adjusted their composition to match mixture seen at native site
-Suggests group trait is locally adapted
