This document discusses different theories for how altruistic behavior evolved in animals despite natural selection favoring selfish behavior. It describes theories of group selection, kin selection, and reciprocal altruism. Group selection proposes that groups with more altruistic members are more likely to survive. Kin selection explains that animals help relatives to increase indirect fitness. Reciprocal altruism occurs when organisms help each other with the expectation of future help in return. The document analyzes these theories in terms of evolutionary biology to explain the prevalence of altruism in animal societies.

1. Birupakshya Paul Choudhury
M.Sc. 3rd semester
Dept of Life Science and Bioinformatics
ASSAM UNIVERSITY

3.  Derived from : French - “Autrui” meaning other people
Latin - “Alter” meaning other
 The term was Coined by- Aguste Comte (French)
 Altruism is a type of social behaviour where the actor is harmed
while others get benefit
 In evolutionary biology, an organism is said to behave altruistically
when its behaviour benefits other organisms, at a cost to itself
 Costs and benefits are measured in terms of reproductive fitness

4.  Why did Altruistic behaviour evolve where natural selection persists
 In a group there are members who are selfish, so how can the
altruists thrive in the population
 Idea of altruism seems to go completely against the Darwinian idea
of ‘survival of the fittest’
??!!!

5.  To explain the altruistic behaviors of animals in the light of
evolution, we need to discuss the following:
A. Group selection
B. Kin selection
C. Reciprocal altruism
 In The ‘Descent of Man’ (1871), Darwin discussed origin of altruistic
and self-sacrificial behaviour among humans
 Almost all animals including humans show altruistic behaviour in
their respective society
 Lets find out the reasons behind Animal altruism

6.  It is a type of natural selection, that acts on all members of a group
i.e. the whole group is favored over another group
 Defined as a selection which evolves according to fitness of groups
 Has two Concepts- 1) Old Concept
2) New Concept

7.  In 1960, Wynne Edwards argued that individual selection could
not explain subordination of selfish interests to promote group
wellbeing
 For example, in groups consisting of selfish individuals (who
reproduce at the maximum rate), resources would be over
exploited, and the group would go extinct. In contrast, groups
consisting of cooperative individuals who restricted their birth
rate would not over exploit their resources, and not go extinct
 This came to be known as the Old concept of group selection

8.  During the 1960s and 1970s a large body of theoretical work was piled up
against the idea of Wynne Edwards’ Old Concept
 Maynard Smith (1976) showed that group selection would not work if the
number of individuals who disperse and reproduce elsewhere (successful
migrants) is greater then one per group
 Empirical works showed that individuals who were reproducing at the rate
that maximized their lifetime reproductive success, and were not practising
reproductive restraint
 Basic idea behind this concept is at certain stages of an organism's life
cycle, interactions take place between only a small number of individuals. &
under these conditions, cooperative behaviour can be favored.

9.  Sometimes referred to as ‘trait-group selection’ or ‘demic selection’
or ‘intrademic’ selection
 Difference between the old and new group selection models is that
the new group selection models rely on within-population
(intrademic) group selection,
 Whereas old group selection theory worked on between-population
(interdemic) group selection
Groups
Selfish
Altruists

10.  “Kin selection” was coined by Maynard Smith
 Also known as Inclusive Fitness Theory
 Here, an individual has the tendency to help its relatives
 The inclusive fitness theory (commonly known as Kin selection) was
proposed by Hamilton (1964)- HAMILTON’s RULE
let B = Benefit to Recipient
let C = Cost to Actor
let r = Coefficient of their genetic relatedness
In this case, An allele for an altruistic behavior will be favored if:
Br – C > 0
 r is the probability that homologous alleles present in different
individuals are “identical by descent”.
William
Hamilton

11.  Jerram Brown pointed out that the inclusive fitness of an individual
is dividedinto two components:
I. ‘Direct Fitness’
II. ‘Indirect Fitness’
 Direct fitness is gained through the production of offspring
 indirect fitness through aiding the reproduction of nondescendent
relatives

12.  Basis of this behaviour: A gene that a particular individual carries
may pass to the next generation through a related animal
 Forego reproduction: Eusociality

13.  Robert Trivers coined and introduced the theory of
‘reciprocal altruism’ (1971)
 In this type of altruism, the altruist acts in a manner that
temporarily reduces its fitness with the expectation that
the beneficiary organism will act in a similar manner at
a later time
 This form of altruism may occur among unrelated
individuals
 Trivers suggested that two conditions must be met:
I. Cost must be ≤ to the benefit received.
II.Individuals that fail to reciprocate must be
punished.
Robert Trivers

15. RECIPIENT BENEFITS
RECIPIENT HARMED
ACTOR BENEFITS ACTOR HARMED
COOPERATIVE ALTRUISTIC
SELFISH SPITEFUL

16. BIG question to be answered
But we have some examples
Helping the needy
Blood donation
BIG question to be answered
But we have some examples
Exchange gifts
Giving seat in the
bus to old/women
Giving away something
permanently for loved
ones
Giving the child to
childless uncle in
joint families
………… and many more
Caring for pets
Working for animal
rights
Sacrificing self for
Nation

18. 1. Alan Grefen ‘Natural selection, Kin selection and Group selection’
2. David Sloan Wilson ‘A Theory of Group Selection’ (1975)
3. Joan B. Silk ‘Reciprocal altruism’
4. Kevin R. Foster, Tom Wenseleers, & Francis L.W. Ratnieks ‘Kin
selection is the key to altruism’(2005)
5. Martin Zwick, Jeffrey A. Fletcher ‘Levels of Altruism’(2014)
6. Stuart A. West, Andy Gardner & Ashleigh S. Griffin ‘Altruism’
7. S. A. West, A. S. Griffin, A. Gardner‘Social semantics: altruism,
cooperation, mutualism, strong reciprocity and group selection’
(2007)

19. URLs:
1. http://science.jrank.org/pages/264/Altruism.html
2. http://plato.stanford.edu/entries/altruism-biological/
3. https://en.wikipedia.org/wiki/Reciprocal_altruism
4. http://www.lse.ac.uk/philosophy/blog/2015/06/19/where-does-altrui
5. http://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2006.01258