LIFESCI 7B Lecture Notes - Lecture 5: Evolutionarily Stable Strategy, Reciprocal Altruism, Worker Bee
10 Jun 2018
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45.6: Social Behavior
● Collaborative social behavior (like whale wave washing) can be beneficial
Group selection is a weak explanation of altruistic behavior.
● group selection Selection caused by the differential success of groups rather than individuals.
○ Idea is that it favors altruistic groups that help eachother and work as a unit (rather than one of
selfish individuals)
● Probably not important in evolution of altruism; selfish activities probably increase individual fitness
more than altruism would
○ Altruism under group selection is typically not an evolutionarily stable strategy; can be
overthrown by “selfish” strategies
■ Organisms do not act for the good of the species!!! All natural selection
● Traits disadvantageous to an individual are selected against, even if beneficial to
the population as a whole
○ evolutionarily stable strategy A type of behavior that cannot readily be driven to extinction by
an alternative strategy.
Reciprocal altruism is one way that altruism can evolve.
● reciprocal altruism The exchange of favors between individuals (can be unrelated, like in vampire
bats that regurgitate extra food to others so that the favor can one day be returned)).
○ individuals have to be able to recognize each other and remember previous interactions.
The concept of kin selection is based on the idea that it is possible to contribute genetically to future
generations by helping close relatives.
● kin selection is based on the idea that it is possible to contribute genetically to future generations by
helping close relatives survive and reproduce.
○ Animal is twice as closely related w/ its offspring than neice/nephew; so helping a sibling
produce two offspring=same net contribution as having one offspring
■ So it’d be beneficial if one animal helps his sibling have 3+ offspring
■ “I’d die to save 2 brothers or 8 cousins”
● If rB>C, altruism (in kin selection) can evolve (hamiltonian equation)
○ r=degree of relatedness between recipient and donor
○ B=benefit of behavior to recipeint (how many individuals does behavior save?)
○ C=cost of behavior to donor
● Example: bugs who spend lives defending rest of colony from predator; don’t have own offspring but
help others survive to produce even more
○ eusocial Describes behavior most commonly observed in species of Hymenopteran insects, in
which they have overlapping generations in a nest, cooperative care of the young, and clear and
consistent division of labor between reproducers (the queen of a honeybee colony) and
nonreproducers (the workers).
■ In bees, sisters are more closely related than mother/offspring; makes sense for worker
bee to help queen bee create more sisters than to reproduce herself
● can result in a huge colony of related individuals all working collectively; entire colony can be refered to
as a single “superorganism”
21.3: Evolution and the Hardy Weinberg Equilibrium
Evolution is a change in allele or genotype frequency over time.
● Change in genetic makeup=evolution
● Does not specifiy a mechanism for this change
The Hardy–Weinberg equilibrium describes situations in which allele and genotype frequencies do not change.
● Frequencies only change when specific forces act on population
● Hardy-Weinberg equilibrium A state in which particular allele and genotype frequencies do not
change over time, implying the absence of evolutionary forces.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Collaborative social behavior (like whale wave washing) can be beneficial. Group selection is a weak explanation of altruistic behavior. Group selection selection caused by the differential success of groups rather than individuals. Idea is that it favors altruistic groups that help eachother and work as a unit (rather than one of selfish individuals) Probably not important in evolution of altruism; selfish activities probably increase individual fitness more than altruism would. Altruism under group selection is typically not an evolutionarily stable strategy; can be overthrown by selfish strategies. Organisms do not act for the good of the species!!! Traits disadvantageous to an individual are selected against, even if beneficial to. Evolutionarily stable strategy a type of behavior that cannot readily be driven to extinction by the population as a whole an alternative strategy. Reciprocal altruism is one way that altruism can evolve.
