Chemical evolution resulted in the evolution of life on earth about 3.8 billion years ago. The primitive cells that resulted from this process gradually gave rise to primitive forms of organisms such as bacteria, algae, fungi and protozoan. Organic evolution is a slow and gradual process involved in evolutionary development of a species or taxonomic group of organisms. The process is the result of innumerable modifications which the living organisms have developed and passed on to their offspring. Hence, organic evolution is described as descent with modifications.