Evolution: This deals with the origin of newer types of organism from the previous ones by modification involving genetic changes and adaptations. Evolution also called as biological & organic evolution it is the change over time in one or more inherited traits found in populations of organisms. Evolution can occur when there is variation or change of inherited traits within a population. The big sources of such variation are genetic recombination, mutation or gene flow. 

 There are four general mechanisms of evolution. The first mechanism is called as natural selection, this is a process in which there is differential survival or reproduction of organisms that differ in one or more inherited traits. The second mechanism is genetic drift, it is a process in which there are random changes to the proportions of two & more inherited traits within a population. The third mechanism is known as mutation that is a permanent change in a DNA sequence. And finally, the fourth mechanism is gene flow this is the incorporation of genes from one population into another.