Sociality
Costs and benefits of social groups
Benefits
• Predation
Costs
• Predation
– Collective detection
– Predator dilution
• Food
– Predator attraction
• Resource competition
• Disease transmission
– Information sharing
– Cooperative hunting
Social interactions
Behavior towards others depends on
costs and benefits to actor and recipient
and genetic relatedness between the two
Fitness of recipient
Fitness of actor
+
-
Altruism
Spitefulness
+
Cooperation
Selfishness
Genetic relatedness
• Sharing copies of gene from same relative (identical
by descent)
• Coefficient of relatedness (r) = average proportion of
genes identical by descent
0.50 = Parent, full sibling
0.25 = Grandparent, half sibling,
aunt/uncle, nephew/niece
0.125 = First cousin
“Would I lay down my life
to save my brother?
No, but I would to save
two brothers or eight cousins.”
Approximate quote by J.B.S. Haldane
Types of fitness
•
•
•
•
Own offspring = direct fitness
Related offspring = indirect fitness
Direct + indirect = inclusive fitness
Kin selection = process of maximizing
inclusive fitness
Hamilton’s rule
• In order for altruistic behavior to occur
C
Costs and benefits of social Groups
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