The term evolution was given by Herbert Spencer. Evolution means gradual change from one form to another. It means to unroll or to unfold or to reveal the hidden potential. The change in non-living things is called as inorganic evolution while change in living organisms is called organic evolution. Darwin defined evolution as “descent with modifications”. According to Dobzhansky “Nothing in biology makes sense except in the light of evolution”.
Every change is not evolution like metamorphosis of Frog, change in ecosystem etc. Evolution is change between successive generations. Often evolution is defined as formation of complex forms, but complexity is never the aim of evolution. Aim of evolution is fitness of an Organism with surrounding conditions or environment. If complexity had been the aim of evolution, the parasites like bacteria, viruses are vanished. Parasites show simplification in its structure in course of evolution, successful feeding and breeding are two main objectives of living organisms and for this complexity is not mandatory. Evolution is continuous process. It never stops because environment never remains constant. There is no climax of evolution. It is not goal oriented process. It is not direct process in terms of determinism. It is stochastic process that means a process which we cannot say with 100% accuracy.
The
unit of evolution is population.
Driving
force of evolution is natural selection.
Unit
of natural selection is individual.
Raw
material for evolution is variation.
Ultimate
source of variation is mutation.