Forms exist in the form of populations due to heterogeneity of the external environment.These groups of organisms are resistant in time and space, but the number of individuals from time to time subject to change.
On the basis of family ties or similar behavior in animal populations can be divided into even smaller groups (prides of lions, flocks of birds or fish).But these groups do not have such stability as the population itself: under the influence of external conditions, they may break or mixed with others, ie,long support themselves, they can not.
organisms comprising the population are interconnected in a variety of ways: they can compete for limited resources (food, territory, individuals of the opposite sex, etc.), eat
each other or together to defend themselves against predators.Internal relationships groups usually difficult and inconsistent.
Some individuals in a population respond differently to changing environmental conditions."Screenings" sick or debilitated organisms can improve the quality of the group and increase its overall viability and resistance to external aggressive factors.
Within the population there is a constant exchange of hereditary material, while individuals from different populations interbreed much less.Therefore we can say that each group has its own inherent only to her gene pool in which different alleles of genes, as well as their encoded symptoms occur with some frequency.Under the influence of such isolation of individual populations may increase the internal diversity of the species, which is useful for securing the new conditions of life.The changes in the properties of populations originated even the formation of new species.
all evolutionary transformations occur at the population level, so it is called the elementary unit of evolution.Preconditions evolutionary transformations are changes in the genetic apparatus - mutations that appeared, spread, fixed and accumulate in the population's gene pool.
Most mutations do not appear outwardly as they are recessive and dominant genes are suppressed in the alleles.However, inbreeding hidden recessive alleles can go in the homozygous state, and appear in the phenotype.Thus, mutations, even in the heterozygous state, and not appearing at once, hidden supply material for possible evolutionary transformations.