According to the Hardy-Weinberg model, evolution will not occur if the following conditions are met: mutation is not occurring, natural selection is not occurring, the population is infinitely large, all members of population breed, all mating is totally random, everyone produces the same number of offspring, and there is no migration in or out of population. In the real world, some of the conditions can never be met.
Biologists generally define evolution as being the sum total of inherited changes in the individual members of a population and measurable as a change in the frequency at which certain alleles occur in the gene pool. In 1908, Godfrey Hardy and Wilhelm Weinberg proposed that gene pool frequencies are inherently stable but that evolution nonetheless occurs virtually all the time because the seven conditions in their model are rarely met. These conditions such as mutation, mate choice, natural selection and migration are all evolutionary influences, and populations in the real world do not exist without them. In fact, only in rare situations are any of the seven conditions met, and some of them, such as having an infinite population or having all members of the population breed in equal numbers, are never possible. The natural conclusion of the Hardy-Weinberg model is that evolution is inevitable in the real world.