There are three main ways of speciation.
The first is a simple view conversion. In the course of evolution, species A changes and turns into species B. This process is called phyletic speciation. In this case, the number of species does not increase.
The second path is called hybridogenic. It is associated with the merger of two existing species A and B and the formation of a new species C. Species A and B in this case can be preserved.
The third way of speciation is due to divergence, that is, the division of one ancestral species into several new species. This is the way, basically, and the evolution of life on Earth went.
Darwin proved that in nature there is a constant process of the emergence of new species on the basis of the existing under the influence of the driving forces of evolution. He considered only the divergent pathway of speciation. The phyletic and hybridogenic pathways were discovered later.
According to modern concepts of evolution, the formation of a new species occurs within the population – an elementary unit of evolution.
Populations are genetically open systems. And while there is an exchange of genes between them as a result of the migration of individuals, the species remains a single genetically closed system. The emergence of isolation between the two populations leads to the accumulation of differences in them, preventing the crossing of individuals. Populations become genetically closed systems and, therefore, new species.
Speciation is an evolutionary process of transformation of genetically open systems (populations) into genetically closed systems (new species).
Speciation is a complex and lengthy process with intermediate stages.
The action of isolation is undirected, but it is a prerequisite for enhancing genetic differences between populations. If the isolation continues for a long time, then multidirectional natural selection leads to a divergence of the characteristics of populations – divergence.
As a result, populations become species or races. Maintaining isolation leads to an increase in the differences between the species, and they turn into subspecies. If the increasing differences between subspecies will prevent them from crossing, then they have become genetically closed systems. Reproductive isolation has developed between them. Subspecies evolved into new species.
Speciation factors are:
- prerequisites for evolution: mutational and combinative variability, population waves, gene drift, isolation;
- driving forces of evolution: the struggle for existence, natural selection.