Stability of the population and species over the number of generations is met under the following conditions

$(i)$ No Mutation Sudden appearance of variations are called mutations. There should not be either gene or chromosomal mutation. Mutation causes changes in gene frequency

$(ii)$ No Gene flow (Gene Migration) Within the gene pool of a given breeding population there is a continuous interchange of alleles between organisms. Gene flow refers to the movement of alleles from one population to another as a result of interbreeding between the members of two population. There must not be gene flow between the population

$(iii)$ No Genetic Drift Genetic drift is also known as 'Sewall Wright Effect' (named after its discoverer). It is random in gene (allele) frequency. It occurs only by chance. It is non directional. Genetic drift can cause elimination of certain alleles or fixation of the other alleles in the population. Genetic drift refers to a change in the population of alleles in the gene pool. So genetic drift must not occur

$(iv)$ No Genetic Recombination The alleles of the parental linkage groups separates and new associations of alleles are formed in the gamate cells, this process is known as genetic recombination. Thus, crossing over during meiosis is a major source of genetic variation within population.

Offspring formed from these gametes showing 'new' combination of the characteristics are called recombinants. There is no genetic recombination

$(v)$ No Natural Selection Pressure There must be no natural selection pressure with respect to the alleles in question.

According to Hardy-Weinberg Principle, gene frequencies will remain constant if all above five conditions are met