Kashmeera N.A.Kashmeera N.A.

II Sem MSc.ZoologyII Sem MSc.Zoology

Roll no:37Roll no:37

Christ collegeChrist college

Natural selection has shaped the behaviour of different animal species in accordance with the demands of their different life styles; as the way of life of a species and its form change over evolutionary time,so does its behaviour.

Under natural conditions,some of the variability between individuals would affect their ability to survive and reproduce successfully.

Those variants that were more successful would leave more surviving offspring and hence their frequency would increase in the population over successive generations

This is the main reason that behaviour evolves and that different species have come to behave differently,because animals only breed with their own species & they can evolve characters independently in accordance with the demands of their surroundings

This type of adaptive evolution is well illustrated by the Kittiwakes

One of the most spectacular displays is the courtship of male peacock.Comparing the displays of related species can give us a clue about their evolutionary origins.

During evolution new species form by splitting of old ones.

The isolated populations then evolve independently in their different environments and their characteristics often diverge.

Mating between such distinct populations may result in sterile hybrids and result in few surviving young ones.

In such circumstances natural selection favours distinct colouration and displays in the 2 groups so that they can readily recognize and mate with members of only their own population.

Once this has happened speciation occurs.

Sceloporus lizards-Males defend their territory and try to attract females with head-bobbing which is different in different species.

Sometimes recognition of the members of the same species is based on learning by the young of the appearance of their parents

In early 1960s W.D.Hamilton developed genetical theory for evolution of behaviour.

This theory revolutionized study of animal social behaviour.This approach is referred to as sociobilogy

Sociobiology is a field of scientific study which is based on the assumption that social behavior has resulted from evolution and attempts to explain and examine social behavior within that context.

.

E. O. Wilson, a central figure in the history of sociobiology.

While the term "sociobiology" can be traced to the 1940s, the concept didn't gain major recognition until 1975 with the publication of Edward O. Wilson's book, Sociobiology: The New Synthesis.

““Every man must decide whether he will walk in the Every man must decide whether he will walk in the light of creative altruism or in the darkness of light of creative altruism or in the darkness of destructive selfishness”destructive selfishness”

– – Martin Luther King JrMartin Luther King Jr

•On occasion, some animals behave in ways that reduce their individual fitness but increase the fitness of others

This kind of behavior is called altruism

For example

An adult Ringed Plover will pretend to have a broken wing.

to draw the enemy away from its nest or young.

Such altruistic act serves to increase the chances of survival of the offspring but often at some risk to the parent.

In naked mole rat populations, nonreproductive individuals may sacrifice their lives protecting their reproductive queen and kings from predators

Vampire bats will regurgitate and feed blood that they have collected from their prey to a hungry conspecific

““You scratch my back & I will scratch yours”You scratch my back & I will scratch yours”

Altruistic behavior toward unrelated individuals can be adaptive if the aided individual returns the favor in the future.This type of altruism is called reciprocal altruism.

Eg-Olive baboon

In them male will always help an unrelated male in troop to distract the attention of a third male that is guarding a receptive female

The soliciting male will take over female while the other two are engaged in dispute.

In future the favour is returned.

Kin selection is the natural selection that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction.

Charles Darwin was the first to discuss the concept of group/kin selection.

In the "The Origin of Species", he wrote clearly about altruistic sterile social insects

Altruistic suicide?Altruistic suicide?

•In many social insects, workers not only forego reproduction, but also their own life, “for the good of the colony”

Florida scrub jay is a communally breeding bird in which the offsprings assist the parents in rearing subsequent broods.

These are their own siblings and by helping to rear them they are in effect spreading copies of their own genes to the future.

In the 1930s J.B.S. Haldane had full grasp of the basic quantities and considerations that play a role in kin selection.

He famously said that, "I would lay down my life for two brothers or eight cousins".

Haldane’s father father’s brother

Genetic relatedness

50%

(1/2)

Genetic relatedness

50%(1/2)

HaldaneBrother’s son

(Haldane’s cousin)

Genetic relatedness 50%

(1/2)

Genetic relatedness

1/2x1/2=1/4

Genetic relatedness

½ x ½ x ½ = 1/8

Hamilton’s Rule and Kin SelectionHamilton’s Rule and Kin Selection

Hamilton proposed a quantitative measure for predicting when natural selection would favor altruistic acts among related individuals.

The three key variables in an altruistic act are:

The benefit to the recipient.

The cost to the altruist.

The coefficient of relatedness.[The coefficient of relatedness is the probability that two relatives may share the same genes.]

Natural selection favors altruism when the benefit (B) to the recipient multiplied by the coefficient of relatedness (r) exceeds the cost (C) to the altruist.

rB > C

This inequality is called Hamilton’s rule.

Hamilton’s ruleHamilton’s rule

Belding’s Ground squirrels will warn others of the presence of a predator, even though making such a call may draw the attention of the predator to itself.

The inclusive fitness of an organism is the sum of its classical fitness and the number of equivalents of its own offspring it can add to the population by supporting others .

more generalized than strict kin selection, which requires that the shared genes are identical by descent.

Inclusive fitness is not limited to cases where kin are involved.

inclusive fitness offers a mechanism for the evolution of altruism.

this leads natural selection to favor organisms that would behave in ways that maximize their inclusive fitness.

The most important text on the subject of biological altruism is "The Selfish Gene" by Prof. Richard Dawkins (1976), which explains in great depth and accuracy the biological nature of selfishness, and argues strongly that biological nature is entirely concentrated on the protection of one's own genes

. It follows that it is possible for an individual to preserve its genes through its own self-sacrifice; if a mother dies in the course of saving her three offspring from a predator, she will have saved 1½ times her own genes (since each offspring inherits one half of its mother's genes).

“Let us try to teach generosity and altruism because we are born selfish” Richard Dawkins (1976).

“Scratch an altruist and watch a hypocrite bleed”. Ghiselin