Kin Selection
EITHER: What kinds of trade-offs shape how much parents invest into each offspring? // Is kin selection
important for humans and if so, explain how. // Compare infanticide in humans, mice and lions. // Do we
understand why animals help their relatives? // Using detailed examples, explain how family life is
organised in non-human primates. // Why do animals sometimes help and sometimes harm their
relatives? // Under what conditions do males help with the care of the young? // When do we expect
conflicts between parents and their offspring? // How can infanticide be adaptive? // Why is there so much
diversity in patterns of parental care in different species? // Why should kin kill kin? // How is parental care
affected by risk of extra-pair copulation?
Cooperation, Altruism and Selfishness
OR: Use Hamilton’s rule to explain under what circumstances it pays to be cooperative or altruistic. //
What prevents animals being more aggressive than they are? // Do humans always choose what is best for
them? // When animals help others are they helping themselves? // Is group living selfish? // How useful is
the Prisoner’s Dilemma for explaining animal behaviour (including humans)? // Discuss with examples the
use of optimality modelling in the study of animal behaviour. // Is cooperation altruistic? // Does altruism
ever occur in human or non-human animals?
Early thinkers
Darwin (1871): The Descent of Man
The sense of morality is a fundamental proposition in the difference between man and the lower
animals
Social instincts, with the aid of active intellect and the effects of habit, naturally posit that humans
should do to one another as they wish done unto themselves.
The development of social behaviour can be seen within the limits of the same tribe, with evidence
that once-barbarous nations became civilized through natural selection of those who acted
cooperatively
Social evolution
Evolution is change is allele frequency in a population, driven by mutation, drift and natural selection
(organisms differ, differences affect survival and reproduction, differences are heritable – three things you
need for natural selection). This leads to a concept of reproductive (direct) fitness – fitness from your own
reproduction.
In evolution, social means the effect of one individual on the direct fitness of another. This leads to a
concept of indirect fitness or the fitness gained from helping others.
Social interactions occur at multiple scales:
In a linkage group (two linked genes)
Between chromosome and homologue
Between nuclei and organelles
Between cells
Within and between species
For example, there is a propensity for cooperation (and competition) within a genome. This is linked the
major transitions (genes to genomes etc.).
, Social interactions are classified by direct fitness effects, i.e. by the effect an action has on an actor’s own
reproduction. For example, altruism is a sacrifice of one’s own reproduction with a positive effect on the
recipient.
Hamilton’s rule
A cooperative behaviour is one that carries a fitness benefit to another individual; it includes mutualism
(benefit to actor and recipient) and altruism (cost to actor, benefit to recipient).
Examples of cooperation: kin selection, adaptive altruism, symbiosis, mutualism, and reciprocal altruism.
The problem of altruism: how is it that animals help each other at a cost to themselves?
Hamilton (1963) The evolution of altruistic behaviour
Recognised the key role of the degree of relatedness between donor and recipient
Hamilton’s rule: rb – c > 0
c = cost to the altruist (reduced reproduction)
b = benefit to the recipient (increased reproduction)
r = degree of relatedness from altruist to recipient
NOTE the importance of b and c is often overlooked
Hamilton’s rule in writing: alleles become more common in a population if the indirect fitness benefit
(which is affected by relatedness/the probability that the individual whose fitness benefits from an
altruistic actor carries the same altruistic allele) is more significant that the direct fitness cost to a given
individual.
“r”
NOT the proportion of shared genes between two individuals
NOT the probability of sharing altruism genes with another individual
Probability of sharing alleles identical by descent (as opposed to by state)
Geometric view of relatedness. It is the probability, over and above the population average, of sharing an
altruism gene in common with a relative (i.e. even if a gene increases in population frequency, the
probability of sharing a gene in common with a sibling is always an extra half). "r" is therefore the degree
to which individuals should value the reproduction of others over their own, suggesting that animals
should have evolved the capacity to distinguish degrees of relatedness.
The concept of inclusive fitness is encapsulated in Hamilton’s Rule
Direct component: personal reproduction
EITHER: What kinds of trade-offs shape how much parents invest into each offspring? // Is kin selection
important for humans and if so, explain how. // Compare infanticide in humans, mice and lions. // Do we
understand why animals help their relatives? // Using detailed examples, explain how family life is
organised in non-human primates. // Why do animals sometimes help and sometimes harm their
relatives? // Under what conditions do males help with the care of the young? // When do we expect
conflicts between parents and their offspring? // How can infanticide be adaptive? // Why is there so much
diversity in patterns of parental care in different species? // Why should kin kill kin? // How is parental care
affected by risk of extra-pair copulation?
Cooperation, Altruism and Selfishness
OR: Use Hamilton’s rule to explain under what circumstances it pays to be cooperative or altruistic. //
What prevents animals being more aggressive than they are? // Do humans always choose what is best for
them? // When animals help others are they helping themselves? // Is group living selfish? // How useful is
the Prisoner’s Dilemma for explaining animal behaviour (including humans)? // Discuss with examples the
use of optimality modelling in the study of animal behaviour. // Is cooperation altruistic? // Does altruism
ever occur in human or non-human animals?
Early thinkers
Darwin (1871): The Descent of Man
The sense of morality is a fundamental proposition in the difference between man and the lower
animals
Social instincts, with the aid of active intellect and the effects of habit, naturally posit that humans
should do to one another as they wish done unto themselves.
The development of social behaviour can be seen within the limits of the same tribe, with evidence
that once-barbarous nations became civilized through natural selection of those who acted
cooperatively
Social evolution
Evolution is change is allele frequency in a population, driven by mutation, drift and natural selection
(organisms differ, differences affect survival and reproduction, differences are heritable – three things you
need for natural selection). This leads to a concept of reproductive (direct) fitness – fitness from your own
reproduction.
In evolution, social means the effect of one individual on the direct fitness of another. This leads to a
concept of indirect fitness or the fitness gained from helping others.
Social interactions occur at multiple scales:
In a linkage group (two linked genes)
Between chromosome and homologue
Between nuclei and organelles
Between cells
Within and between species
For example, there is a propensity for cooperation (and competition) within a genome. This is linked the
major transitions (genes to genomes etc.).
, Social interactions are classified by direct fitness effects, i.e. by the effect an action has on an actor’s own
reproduction. For example, altruism is a sacrifice of one’s own reproduction with a positive effect on the
recipient.
Hamilton’s rule
A cooperative behaviour is one that carries a fitness benefit to another individual; it includes mutualism
(benefit to actor and recipient) and altruism (cost to actor, benefit to recipient).
Examples of cooperation: kin selection, adaptive altruism, symbiosis, mutualism, and reciprocal altruism.
The problem of altruism: how is it that animals help each other at a cost to themselves?
Hamilton (1963) The evolution of altruistic behaviour
Recognised the key role of the degree of relatedness between donor and recipient
Hamilton’s rule: rb – c > 0
c = cost to the altruist (reduced reproduction)
b = benefit to the recipient (increased reproduction)
r = degree of relatedness from altruist to recipient
NOTE the importance of b and c is often overlooked
Hamilton’s rule in writing: alleles become more common in a population if the indirect fitness benefit
(which is affected by relatedness/the probability that the individual whose fitness benefits from an
altruistic actor carries the same altruistic allele) is more significant that the direct fitness cost to a given
individual.
“r”
NOT the proportion of shared genes between two individuals
NOT the probability of sharing altruism genes with another individual
Probability of sharing alleles identical by descent (as opposed to by state)
Geometric view of relatedness. It is the probability, over and above the population average, of sharing an
altruism gene in common with a relative (i.e. even if a gene increases in population frequency, the
probability of sharing a gene in common with a sibling is always an extra half). "r" is therefore the degree
to which individuals should value the reproduction of others over their own, suggesting that animals
should have evolved the capacity to distinguish degrees of relatedness.
The concept of inclusive fitness is encapsulated in Hamilton’s Rule
Direct component: personal reproduction
