Altruism, Kin Selection, Kin Recognition, and Inclusive fitness

altruism

• Type of social behavior where the “actor” is harmed while others get benefit

• In evolutionary biology, an organisms is said to behave altruistically when its behavior benefits other organisms, at a cost to itself

• Cost and benefits are measured in terms of “reproductive fitness”

• Pertinent topics:

• Group selection

• Kin selection

• Reciprocal altruism

• Almost all animals show altruistic behavior in their societies (social organizations)

helpful behavior that lowers the helper’s reproductive success while increasing the reproductive success of the individual being helped

how does altruism exist within natural selection

• Why did altruistic behavior evolve where natural selection persist?

• In a group there are individuals who are selfish, so how can the altruists thrive in the population?

• The idea of altruism seems to be completely against the Darwinian idea of “survival of the fittest”

group selection

• Type of natural selection that acts on all members of a group: the whole group is favored over another group

• A selection which evolves according to “group fitness”

• V.C. Wynne Edwards

• J. Maynard Smith (evolutionarily stable strategy -ESS-)

Groups or species with self-sacrificing (altruistic) individuals are more likely to survive than those without altruists, leading to the evolution of group-benefiting altruism

• Sterile castes of social insects

• BUT: natural selection acting on differences among individuals within a population or species will usually have a stronger evolutionary effect than group selection acting on differences among entire groups

If GS favors a trait that involves reproductive self-sacrifice while natural selection acts against it, natural selection seems likely to trump GS

the process that occurs when groups differ in their collective attributes and the differences affect the survival chances of the groups

direct selection

the process of natural selection that occurs when hereditarily distinctive individuals differ in the number of surviving offspring they produce or number of genes they pass on to subsequent generations

direct fitness

a measure of the reproductive or genetic success of an individual based on the number of its offspring that live to reproduce

“Kin” or indirect selection

the process that occurs when hereditarily distinctive individuals differ in the number of non-descendant relatives (not their offspring, but its relatives) they help survive to reproduce

• “Kin selection” was coined by Maynard Smith (1964)

• It is a type of natural selection

• It is based on the concept of inclusive fitness, which is made up of individual survival and reproduction (direct fitness) and any impact that an individual has on the survival and reproduction of relatives (indirect fitness).

• Animals are more likely to behave altruistically towards their relatives then towards unrelated members of their species

• Coefficient of relatedness: the probability that an allele in one individual is present in another because of both individuals have inherited it from a recent common ancestor; the probability that two individuals share an allele due to recent common ancestry

indirect fitness

→ measure of the genetic success of an altruistic individual based on the number of relatives (or genetically similar individuals) that the altruist helps reproduce that would not otherwise have survived to do so

→ the reproduction of non-descendant relatives

inclusive fitness

→ a total measure of an individual’s contribution of genes to the next generation by direct and/or kin (indirect) selection

→ If an individual produces one offspring itself and helps a sibling produce three offspring...

• Direct fitness = 1 x 0.5 = 0.5 (the one offspring that owes its existence to the individual)

• Indirect fitness = 3 x 0.25 = 0.75 (the three offspring that would not have existed except for the individual’s help)

• Inclusive fitness = 0.5 + 0.75 = 1.25

behavioral strategy

an inherited behavioral pattern that is in competition with other hereditarily different behavior patterns in ways that have the potential to affect an individual’s inclusive fitness. E.g., the willingness of individuals to assist close relatives even though their help reduce their direct fitness

the inclusive fitness theory

was proposed by William Hamilton (1964): “Hamilton’s Rule”

• B = Benefit to Recipient

• C = Cost to Actor

• r = Coefficient of their genetic relatedness

• rB - C > 0

• In other words: a gene for altruistic behavior would be favored

by natural selection if: rB > C

• The cost for the actor ( C ) is low

• The benefit for the recipient (B) is high

• The action is between close relatives

inbreeding depression

the reduced survival and fertility of offspring of related individuals

Habsburg Chin/Jaw

• Fifteenth century European royalty

• Mandibular prognathism due to inbreeding

• Other associated physical illnesses

• Seems to have disappeared but may still be in gene pool

Richard Dawkins: “The Selfish Gene”

It explains the biological nature of selfishness, and argues that biological nature is entirely concentrated on the protection of one's own genes

• It is possible for an individual to preserve its genes through its own self-sacrifice.

• If a mother dies while saving her 3 offspring from a predator, she will have saved 1½ times her own genes (since each offspring inherits one half of its mothers' genes: ½ x 3 = 1.5)

helpers

are often older offspring of the parents and sibs of the young

helpers at the nest

• To describe a social structure in which juveniles and sexually mature adolescents of either one or both sexes, remain in association with their parents and help them raise subsequent broods or litters, instead of dispersing and beginning to reproduce themselves.

• Mostly in birds

• A simple form of co-operative breeding

• Uli Reyer (1984) & the pied kingfishers

• Year-old males that are unable to find mates become primary helpers that bring fish to their mothers and their nestlings while attacking predatory snakes and other nest enemy

• Some help unrelated pairs = secondary helpers

• Some sit out the breeding season = delayers

Result:

• Primary helpers have higher inclusive fitness (= 0.41 + 0.58 = 0.99) than secondary helpers (= 0.84) or delayers ( = 0.29)

cooperative breeding

• The conditions that favored its evolution are still unclear

• Griesser et al. (2017): “family living acted as an essential stepping stone in the evolution of cooperative breeding in the vast majority of species”

• Two-step framework or “the two-transition model” better explains the geographic distribution (environmental factors) of cooperative breeding

• Many of the hotspots for this trait (South Africa, Australia, northern South America): places that have undergone dramatic climate change

The formation of families is associated with more productive and seasonal environments and the subsequent evolution of cooperative breeding is linked to an increase in the variability of environmental productivity

what would be the advantage to a helper at the nest?

• Competition for home sites (nests, dens)

• Lack of appropriate mates

• Delay of the offspring’s “going out into the world” until he is bigger/stronger/smarter/more experienced

• More members in his family (Kin selection): probably an advantage