ALTRUISM AND EVOLUTION
Altruism is a social behaviour. From an evolutionary point of view, a behaviour is social if it has
consequences for both the actor and another individual, the recipient. Social behaviour can be
categorized according to whether their consequences for the actor and recipient are beneficial,
increasing fitness or decreasing fitness. Altruism is when a behaviour reduces the fitness of the actor,
but increases the fitness of the recipient. Altruistic behaviour actually increases inclusive fitness
(fitness of the individual plus the fitness of relatives).
There are two concepts to explain the way in which natural selection helps in the development of
sociality. They are group selection concept and kin-selection concept.
Group selection concept is based on the view that the natural selection operates at group level,
instead of at the more conventional level of the individual. Many species have a social structure in
which individuals form groups and interaction among members within each group is much more
frequent than interaction of individuals across groups. Group selection is possible when the
aggregation of individuals into groups with a particular social structure promotes the fitness of
group members.
Example (1) Wolves may associate in packs because this facilitates the capture of prey.
Example (2) Chimpanzees may live in groups because this provides defence against predators and
promotes the defence of valuable territory.
Example (3) Cooperative hunting such as among lions and other social carnivores.
Kin Selection Concept
Kin selection is a subcategory of group selection, where the group is formed of related organisms.
Group selection and kin selection are two concepts but one process. Kin selection favours the
reproductive success of organism’s relatives, even at the cost to the organism’s own survival and
reproduction. Evolutionists have often been puzzled by the occurrence of certain traits whose
evolution seems difficult to explain. For instance, altruism is a characteristic feature of many social
animals. Altruism is a form of behaviour that benefits other individuals at the expense of the one
that performs the action (the altruist). For example, a male Baboon sacrificing itself to protect
the troops. Since the altruistic individual dies, selection appears to act to weed out genes for
altruism out of population. It might be expected that natural selection would foster the
development of selfish behaviour and eliminate altruism. However it is interesting to see that
natural selection always favour altruistic behaviour since it increases the reproductive fitness
of the population as a whole. It has been proposed that in these cases, the actual units of selection
is group but not the individual. Population lacking them die out. It is noticed that the beneficiaries of
altruistic behaviour are usually relatives or kins. They carry the same genes, including the genes that
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promote altruistic behaviour. Thus the more likely explanation of the phenomenon of altruism is kin
selection.
Parental care is a form of altruism readily explained by kin selection. The parent spends some
energy caring for the progeny because it increases the reproductive success of the parent’s genes. A
particularly valuable contribution of the theory of kin selection is its explanation of the evolution of
social behaviour among ants, bees, wasps and social insects. In the honeybee, for example, the
female workers build the hive, care for the young, and gather food, but they are sterile; the queen
bee alone produces progeny. It would seem that the workers’ behaviour would in no way be
promoted or maintained by natural selection. Any genes causing such behaviour would seem likely
to be eliminated from the population, because individuals exhibiting the behaviour do not increase
their own reproductive success, but that of the queen. The situation is, however, more complex.
Some of these behaviours can be explained by the fact that the recipient of the”altruistic” behaviour
is a relative of the donor. It is important to define the coefficient of relatedness.
Coefficient of relatedness (r)
The coefficient of relatedness (r) between two individuals is defined as the percentage of genes that
those two individuals share by common descent. That may seem a little complicated, but it is
actually easier to calculate than to define. Consider the simplest example of calculating the
coefficient of relatedness of a parent and its offspring in a diploid system. The offspring inherit ½ of
their genome from a particular parent, so that they will have a coefficient of relatedness of 0.5. If
you take this one generation further,the offspring’s offspring (grandoffspring) will have ½ of the
genome of its parent, and consequently ½ x ½ = ¼ of its genome from its grandparent. Thus, a
grandparent and grandoffspring have a coefficient of relatedness (r) of .25. In general r = 5n where
‘n’ is the number of “generational links”.
The coefficient of relatedness or coefficient of relationship (r) is how related you are to a particular
family member. The closer the number is to 1, the closer the relative; the closer the number is to 0
the more distant the relative. A high (r) between two people means their offspring will be more
inbred. Everyone gets half their autosomal DNA from each parent, making the coefficient of
relationship between parent and child ½ . For example, the coefficient of relatedness between you
and your full sibling is ½ (0.5), which is obtained from ¼ + ¼ as in the diagram below.
mom
dad
½
½
sister
you
½
sister
½ x ½ = ¼ = 0.25
½
you
½ x ½ = ¼ = 0.25
¼ + ¼ = ½ = 0.5
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You and your full sister are ¼ similar via your mother, and ¼ similar via your dad, making your
total similarity equal to ½.
Half-Siblings
If someone else share a dad but not a mom, then they are half-siblings. What makes two children
full-siblings or half-siblings is, how much genetic information or DNA, they share. Hence similarity
between you and your half sister is only ¼ (0.25).
Similarly, grandparents and grandchildren have coefficient of relatedness, ¼ (0.25), great
grandparents and great grandchildren have coefficient relatedness, 1/ (0.125).
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Hamilton’s Rule
As close relatives share more genes than distant ones, we would expect a balance between the cost
to the donor and the relatedness of the recipient. This idea is captured by Hamilton’s Rule which
says that the fitness benefit to the recipient must be greater than the fitness cost to the donor (C).
The benefit to the donor is given by the total fitness benefit (B) multiplied by the relatedness (r) of
the recipient to the donor. Thus, for altruism to occur, rB>C. Thus altruism is expected to be
uncommon except among highly related individuals.
Altruism is favoured when rb-c>0. Altruism could evolve if the fitness benefit to the recipient (b),
weighted by its relatedness to the actor (r), outweighs the fitness cost of the actor (c).
So, Hamilton’s rule states that a gene for altruism spreads if the genetic profit, calculated as the
recipient’s extra offspring production multiplied by the relatedness of the altruist and the recipient,
minus the genetic loss, which is the fall in the altruist’s offspring production, is greater than zero.
Reciprocal Altruism:In a series of ground-breaking contributions to biology in the early 1970s Robert Trivers introduced
the theories of reciprocal altruism (1971), parental investment (1972), and parent-offspring
conflict (1974).
Reciprocal altruism is the name given to the provision of goods and/or services by one organism to
another, when the cost incurred by the donor in such provision will later (or sometimes,
immediately) be repaid in the form of a reciprocated act-a returned favor, of sorts. Reciprocal
altruism is not unconditional. Firstly the act of altruism must give rise to a surplus of cooperation, in
the sense that the gains to the beneficiary must be perceived to be meaningfully larger than the costs
to the benefactor. Secondly the act of altruism should be reciprocated by the original beneficiary if
the
situation is later reversed. Failure to do so will usually cause the original benefactor to
withdraw future acts of altruism.
In order for the altruist not to be exploited by non-reciprocaters, it would be expected that reciprocal
altruism can only exist in the co-presence of mechanisms to identify the punish “cheaters”. This
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strategy of behaving altruistically at first, but withdrawing aid in the case of non-reciprocation is
similar to the tit for tat strategy in game theory.
A potential example of reciprocal altruism is blood-sharing in the vampire bat, in which bats feed
regurgitated blood to those who have not collected much blood themselves knowing that they
themselves may someday benefit from this same donation; cheaters are remembered by the colony
and ousted from this collaboration.
MULTIPLE CHOICE QUESTIONS AND ANSWERS
1. The idea that an altruistic gene will be favoured if r>C/B, where r is the coefficient of
relatedness, B is the benefit to the recipient of the altruism and C is the cost incurred to the
donor, is known as
1. red queen hypothesis.
2. handicap principle.
3. Hamilton’s rule
4. Competitive exclusion principle.
2. Altruism to occur,
1. rB=C
2. rC-b>0
3. rB>C
4. rC-b=0
3. Vampire bats regurgitate food in order to feed a starving member of their group. This is an
example of
1. group selection
2. reciprocal altruism 3. selfish behaviour
4. K-selection
4. In an altruistic act, if a donor sacrifices ‘C’ offsprings which helps the recipient to gain ‘B’
offspring and the donor is related to the recipient by a coefficient r, under which condition
would kin selection favour this altruistic trait?
1. B>C
2. B>rC
3. rB – C = 0
4. rB-C>0
5. The correct expression of Hamilton rule for the evaluation of altruism is [C = the cost of a
behavioral act to the actor, b= the benefit of that act to a beneficiary, and r = the genetic
relatedness between the actor and the beneficiary]
1. c < b r
2. c < b
3. c r < b
4. r < b c
6. Assume that in terms of ‘genetic fitness’ the ‘benefit’ of performing an altruistic act to a relative
is 500 units and the ‘cost’ involved is 150 units. Following Hamilton’s Rule, the act should be
performed if the relative is a
1. only brother
2. nephew or niece
3. brother or step-sister
4. only step-sister
7. Brothers A and B have the same father but different mothers. B wants A to help him, which
involves both benefits (b) and costs (c) for A. If A incurs a cost of 30 ‘Darwinian fitness units’
in that act, under what condition should help B, following Hamilton’s rule?
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1. only if b > 30
2. only if b > 60
3. only if b > 120
4. only if b > 240
8. Individual A can derive ‘fitness’ benefit of 160 units by helping individual B, but incurs a
‘fitness’ cost of 50 units in doing so. Following Hamilton’s Rule, A should help B ONLY if B is
his
1. brother or sister.
2. first cousin only.
3. cousin or uncle.
4.
nephew or
niece.
9. Worker bees, instead of themselves reproducing, help the queen reproduce. This behaviour is
explained as an example of
1. kin selection
2. group selection
3. sexual selection
4. natural selection
10. In some species of new world monkeys, only one female reproduces in a group. One or more
younger females have suppressed reproduction and assist the reproductive female. This is an
example of
1. sexual selection
2. group selection
3. kin selection
4. reciprocal altruism
KEY
1. Ans. 3
2.Ans. 3
3.Ans.2
4.Ans.4
5.Ans.1
6. Ans.1
Expln:- Kin selection would favour the altruistic act if rB-C>0. In the given question. the
coefficient of relatedness should be 0.5 or more.
Then, 0.5 x 500 – 150 > 0
While if it is nephew or niece, the coefficient of relatedness would be 0.25.
The 0.25 x 500 – 150 < 0
-
25 < 0
Hence the following Hamilton’s Rule the act should be performed if the relative is only brother.
7. Ans.4
Expln:- Since A and B are half-siblings, there coefficient of relatedness, r = 0.25
rb>C
0.25 x 240 > 30= 60 > 30.
8. Ans.1
Expln:- If the B is his cousin, uncle nephew or niece, coefficient of relatedness would be 0.25.
Then based on Hamilton’s rule A cannot help B, because
0.25 x 160 = 40
It is less than the fitness cost, C which is 50. Hence A should help B only if B is his brother or
sister;
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0.5 x 160 > 50 = 80 > 50.
9. Ans.1
10. Ans.3
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