The accumulation is the variations of gradual changes which takes places in primitive organisms over millions of years and new organisms are formed.

There are four ways in which this can do. These are:-

(i) Natural selection: Natural selection may work differently in different location. Due to this, variations may occur which lead to the formation of a new species.

(ii) Geographical isolation: is the isolation of population by physical barriers such as stretches of water, mountain, etc.

(iii) Dna changes: variations during DNA copying often leads to the formation of a new species

(iv) genetic drift: Over generations, genetic drift may lead to the accumulation of different changes which leads to the formation of a new species.