This process can be divided into the following steps:
Spontaneous mutations and the onset of divergence within the same population.
Natural selection of the fittest individuals, continued divergence.
The death of less adapted individuals as a result of the influence of environmental conditions is the continuation of natural selection and the formation of new populations and subspecies.
Isolation of subspecies resulting in the emergence of new species due to reproductive dissociation.
Divergence, or the divergence of signs, is the basis of the evolutionary process. Any species consists of a large number of populations that differ in a number of ways. But the population does not happen to be homogeneous: due to mutational variability, there are individuals in it more and less adapted to the conditions of existence. In populations, recessive mutations that do not manifest themselves phenotypically are constantly accumulating. When conditions of existence change, divergence begins. It lies in the fact that individuals with extreme manifestations of any trait will mainly survive or die out without leaving offspring. The group of individuals that is best suited to new conditions will actively multiply, passing on useful hereditary traits from generation to generation. The least adapted individuals will quickly die out, and individuals with an intermediate value of the trait will gradually be replaced by more adapted ones. Thus, new subspecies and species arise. Not only species diverge, but also genera, families, orders.
Divergence always has the character of group selection of individuals with useful traits due to natural selection. Since the material for natural selection, that is, hereditary changes, arise as a result of various mutations, it is the mutational variability that leads to divergence. As a result of divergence, a whole genus emerged from one species of tits, combining 5 species that feed on various foods. More than 20 species of buttercups have one ancestor appearance. The reason for their divergence was geographical specialization: some species live in swamps, others in meadows, still others in the forest, etc.
This type of isolation is associated with the expansion of the habitat of the species – range. Moreover, new populations fall into different conditions compared to other populations: climatic, soil, etc. Hereditary changes constantly accumulate in the population, natural selection acts – as a result, the gene pool of the population changes and a new subspecies arises. The free crossing of new populations or subspecies can be hindered by rivers, mountains, glaciers, etc. For example, on the basis of geographical factors of isolation from one species of lilies of the valley, a number of species arose over several million years. Speciation along this path is carried out slowly, over hundreds, thousands and millions of generations.