The variation are produced when the new generation reproduces, The second generation produced will have variations that they inherit from the first generation.

The organism can reproduce through two mode of reproduction

(i) Asexual reproduction.

(ii) Sexual reproduction.

In Asexual reproduction is found by the division of parent organism into daughter nuclei. In case of bacteria, bacteria get divided into two individuals, each of them will divide again and give rise to two other organism. The four individual bacteria generated would be very similar with minor difference that occurred due to small inaccuracies in copying of DNA.

In Sexual reproduction involves the fusion of gametes. The offsprings show variations from their parents due to crossing over and exchange of gene segments. They are not exact copies of their parents, due to environmental factors certain favourable variations are also produced. Due to production of variations, sexually reproducing animals show very quick evolution.