Elementary factors of evolution are factors that change the genetic structure of a population.
The main elementary factors of evolution include the mutation process, combinative variability, population waves and gene drift, isolation, and natural selection.
Mutations are abrupt and persistent changes in traits that are inherited.
The mutation process leads to the emergence of new genes. A gene can go from a dominant state to a recessive one (A → a) or vice versa. The structure of the gene can change (A → C).
The mutation process occurs by chance and cannot be a guiding factor. As a result of mutations, material for natural selection is formed.
Combinative variability is the formation of new combinations of already existing genes.
Provides phenotypic diversity of individuals in the population and is also a source of material for natural selection.
Waves of life – periodic and non-periodic fluctuations in population size.
Causes of population waves:
- periodic changes in environmental factors (seasonal fluctuations in temperature, humidity, etc.);
- non-periodic changes (natural disasters);
- development of new habitats (leads to a significant increase in the number of individuals of the species).
Life waves are an important factor in evolution in small populations where gene drift can occur.
Gene drift is a sharp and random change in the concentration of genes and genotypes in the gene pool of a population.
In a small population due to natural disasters (fire, flood, hurricane, etc.), the number of individuals can sharply decrease. At the same time, individuals with rare genes can survive. In the future, these genes will be fixed due to an increase in the frequency of closely related crosses and the gene pool of the population will change.
This means that population waves and genetic drift create material for natural selection.
Isolation is the occurrence of factors that prevent free crossing.
The exchange of genetic information between isolated populations stops, so the differences in the gene pools of populations increase and become fixed. In each of the populations, different changes take place, and they gradually turn into different species.
Isolation is either spatial or biological.
Spatial (geographical) isolation occurs when different populations of the same species are separated by some difficult-to-overcome barriers (water bodies, gorges, forest areas, mountains, swamps, roads) or long distances.
The reasons for biological isolation are biological differences that arise between organisms of the same population. There are four types of biological isolation: ecological, ethological, morphophysiological and genetic.
Ecological isolation is associated with a shift in the timing of flowering, mating, spawning, or with different breeding sites. Ethological isolation is due to differences in the behavior of individuals during the mating season. Morphophysiological isolation is due to differences in the size of individuals or in the structure of the reproductive organs, which prevents mating and fertilization. Genetic isolation is associated with chromosomal and genomic rearrangements that prevent free interbreeding of individuals.
Isolation is a prerequisite for increasing differences in the gene pools of populations.
All the considered elementary factors of evolution act in an undirected manner, but they lead to a change in the ratio of genes and create material for natural selection.