Question

Describe briefly any three factors responsible for speciation.

Answer 1

Speciation is the process in which one or more species arise from previously existing species due to reproductive isolation of a part of its population.

Factors responsible for speciation:

Geographical barriers
Speciation can occur due to formation of extrinsic geographical barriers (such as rivers, mountains, etc)  between two populations which allows no gene flow. 


Natural selection
Darwin and wallace proposed that natural selection is the mechanism by which new species arise from pre existing ones. Natural selection states that there is "struggle for existence" within a population.

Genetic drift
Genetic drift refers to the fact that variations in gene frequencies within populations can occur by chance rather than by natural selection. 

Answer 2

1)Genetic drift

accidental changes which leads to evolution

2)Natural selection

nature select the best ones having positive variation

3)Mutation

chemicals or radiations cause evolution