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Class 10 Class 12
When did life appear on earth ?

 500 million years ago.

What is industrial melanism ?


Explain how natural selection has worked on population of peppered moth in industrial area of England. 

Industrial melanism. It is an example of natural selection shown by peppered moth Biston betularia. The moth had a dull grey coloured body before industrial revolution in England. The colour of moth enabled it to adapt to the light coloured background. After the industrial revolution the environment changed with the deposition of tar soot on the bark of the trees. As a result, light coloured species of moth were easily detected by the predators against the dark bark of trees while the black coloured moth Biston carbonaria increased in number. The change enabled the animal to adjust with the changed environment.

However, with the replacement of coal and petroleum by gas and electricity the situation has changed. Thus the white moth has become abundant with a sharp decline in the number of black. The reason being the decrease in pollution and restoration of grey colour on the trees because of the growth of the lichens on the tree trunk.

Thus industrial melanism is an interesting example of evidence in favour of natural selection.


Discuss geological time scale as evidence of evolution.

Geological time scale. It is estimated that age of our planet earth is about 4.6 x 106 years and first life originated in water (probably seas) about 3.6 x 106 years ago. Geological time scale is the tabulated form showing the sequence and duration of the eras and the periods with their dominant form of life since the beginning of life on the earth.

G. Araduiana developed the first geological time scale. In the geological time scale, the duration of earth's history has been divided as follows :

Era Periods -

Palaeozoic era  has 6 Periods. They are : Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.
Mesozoic era  has 3 Periods. They are Triassic, Jurassic and Cretaceous.
Coenozoic era  has 2 Periods. Tertiary and Quarternary.

Some of the periods are further divided into still smaller time spans called epochs.  Tertiary period 5 epochs namely Palaeocene, Eocene, Oligocene, Miocene and Pliocene.
Quarternary has 2 epochs called  Pleistocene and Recent.



Differentiate apes and man.

Differences between Ape and Man



1. Cranium expanded, maximum brain size 750 cc.

2. Less erect posture.

3. Strong jaws and without well marked

4. Incisor and canine teeth large.

5. Limited use and no manufacture of tools.

6. Not able to speak.

1. Cranium expanded, maximum brain size 2,250 cc.

2. Fully erect posture.

3. Small jaw with a prominent chin.

4. Incisor and canine teeth reduced.


5. Extensive use and manufacture of tools.

6. Able to use spoken and written language.


State and explain any three factors affecting allele frequency in populations.

The allele frequency in a population can be affected in the following ways -:
i. Genetic migration or Genetic drift. - When a section of population migrates to some other region then there is change in the gene frequencies and new allele or gene are added to the population. 
ii. Mutation Mutation leads to the formation of new species and hence change in allelic frequencies.
iii. Natural selection - is the process in which heritable variations that enable better survival are chosen and the organism is enable to produce and leave more number of progeny.

Where did Darwin err in his theory of the “Origin of Species” through natural selection ?

Darwin's theory had following drawbacks :

1. Survival of the fittest. Darwinism can explain the survival of fittest but is unable to account for arrival of the fittest. It is difficult to suppose that small variations could have formed organs like wings and mimicry colouration which are useful only in their fully developed state.

Certain organs can be helpful to the organism only in fully developed state and what about their presence in early stages.

2. Over specialization. Tusks of elephants and the antlers of some deer have overgrown their usefulness.

3. Vestigial organs. A number of vestigial organs persisting generation after generation has no explanation according to Darwinism.

4. Darwin did not differentiate between somatic and germinal variations.