(i) Stabilizing selection (centripetal selection):
1. This type of selection operates in a stable environment.
2. The organisms with average phenotypes survive where as the extreme individuals from both the ends are eliminated.
3. There is no speciation but the phenotypic stability is maintained within the population over generation.
4. For example, measurements of sparrows that survived the storm clustered around the mean and the sparrows that failed to survive the storm clustered around the extremes of the variation showing stabilizing selection.
(ii) Directional selection:
1. The environment which undergoes gradual change is subjected to directional selection.
2. This type of selection removes the individuals from one end towards the other end of phenotypic distribution.
3. For example size differences between male and female alike extremely but different in body weight.
4. Females show directional selection in reflection to body weight.
(iii) Disruptive selection (centrifugal selection)
1. Under homogenous environmental changes into heterogenous environment this type of selection is operational.
2. The organisms of both the extreme phenotypes are selected whereas individuals with average phenotypes are eliminated. This results in splitting of the population into sub-population/species. This is rare form of selection but leads to the formation of two or more different species.
3. It is also called adaptive radiation (e. g.)  Darwin finches -beak size in relation to seed size inhabiting Galapagos islands.

1. Hugo de Vries by his experiment suggest that variations is caused due to mutation among the genetic sequence of an individual.
2. Hugo de vries for the first time gave the term saltation which stands for huge mutation in a single step resulting in speciation.
3. Darwin during his voyage in H.M.S. Beagle he found that living organism share similar features existed from million of years.
4. Evolution is a sequential process that leads to betterment of life forms to cope with change in environment and that is passed to successive generation called as natural selection.
5. Mutation is a random process and direction which is not specific.

Adaptive radiation is the process of evolution of different species in a given geographical area starting from a point and literally radiating to other geographical area habitats.
1. Darwins finches were the small black birds which Darwin observed in Galapagos islands.
2. There were many varities of these birds in the same island.
3. Darwin reasoned that after originating from a common ancestral seed eating stock the finches must have radiated to different geographical areas and undergone adaptive changes especially in their breaks enabling some of them to become insectivorous.
4. Living isolation for long new kinds of finches must have evolved which could survive in the new habitats.
5. Australian marsupials (Kangaroos) also show adaptive radiation
6. Marsupials in Australia and placental mammals in north America are two subclasses of mammals they adapted in similar way to a particular food resources, locomotary skill or climate.
7 They were separated from the ori-on ancestor more than 100 million year ago and each lineage continued to evolve independently despite temporal and geographical separation marsupials in Australia and placenta mammals in North America have reduced varieties of species living in similar habitats with similar way of life their overall resemblance in shape, locomotary mode, feeding and foraging are superimposed upon different modes of reproduction.

1. Natural selection can be explained clearly through Industrial melanism.
2. Industrial melanism is classical case of natural selection exhibited by the peppered moth.
Biston Betularia
1. These were available in two colours, white and black. Before industrialization peppered moth both white and black coloured were common in England (Manchester).
2. Pre-industrialization witnessed white coloured background of the wall of buildings hence the white coloured moths escaped from their predators.
3. Post Industrialization the tree trunks become dark due to smoke and soot let out from the lndustries.
4. The black moths camouflaged on the dark bark of the trees and the white moths were easily identified by their predators (birds).
5. Hence the dark coloured moth population was selected and their number increased when compared to the white moths nature offered positive selection pressure to the black coloured moths.
6. The above proof shows that in a population organisms that can adapt will service and produce more progenies resulting in increase in population through natural selection.

Genetic drift is a mechanism of evolution in which allele frequencies of a population change over a generation due to chance (sampling error). Genetic drift occurs in all population sizes, but its effects are strong in a small population.

Genetic variation is the ALXl gene in the DNA of Darwin's finches is associated with variation in the beak shape. Mild mutation is the ALXl genes leads to phenotypic changes in the shape of the beak as in Darwin finches.

Structures which are similar in origin but perform different functions are called homologous structures that bring about divergent evolution.
Eg: Thorn of Bougainvillea is used for defense and tendrils of Cucurbita are used for climbing but both are homologous structures.

(i) The earliest fossils of the prehistoric man like Ramapithecus lived some 14mya. They were hairy and walked like gorillas and chimpanzees.
(ii) They had a brain capacity of 1300cc.
(iii) They lived on tough food consisting of seeds and savannah grasses and had well developed grains and heavy molars.
(iv) Australopithecus had a brain capacity of 461cc, teeth consisted of small canines and large molars. Good are softer foods consisting of grass, leaves and fruits.

Lamarcks 'theory of acquired character's was disproved by August Weismann who conducted experiments on mice for twenty generations by cutting their tails and Weismann proved that change in the somatoplasm will not be transferred to the next generation but changes in the germplasm will be inherited.