What factors would lead to the rise of a new species ?

The factors that would lead to the rise of a new species are the following : Geographical isolation of a population caused by various types of barriers (such as mountain ranges, rivers and sea). The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of pupulation. Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone. Variations caused in individuals due to a natural selection.