Answer:
Genetic drift, natural selection, genetic variation in population, mutation, speciation, reproductive isolation. These all factors could lead to the rise of a new population, i.e, show patterns of evolution in different ways.
Genetic Variation in the Population: A species may have many populations in different places. Population is involved in this not an individual because the individual can die suddenly, but the population will not die in the sudden way it will continue and lead to the generation of new species.
Genetic Drift: It is the chance of elimination of genes when the part of a population dies during the natural calamity or migrates due to any reason. Some of the population dies, but the remaining part of the population migrants when mates with same or different species may lead to rise of a genetic variability or rise of a new species.
Natural Selection: This theory is given by Darwin, which represented the struggle for existence or elimination of the unfit members. Some members of the population have special genes which are able to grow up or reproduce at the higher level and transfer their special genes to the next generation and so on. Genes of the some members who reproduce the offspring at the higher level will become the strongest element in the gene pool which leads to change in gene frequency of the population and the rise of the new species.
Mutation: Mutation is the major source of the variation. When mutation occurs in the genes the new phenotype produced by the genetic variations, and these variations can have some advantages or some disadvantages, that alters the gene pool. Or when variations occur in the positive way, it will give rise to the new species.
Speciation: When the environmental changes occur or the part of population migrates to the new place due to some variations, may lead to the rise of a new species. If the population becomes adapted and if its members have some genetic variations, i.e, adapted to the new environmental changes give rise to the new population. And, the origin of new species from the existing one with the new acquired characters is known as speciation.
Reproductive Isolation: It is the mechanism which checks the population of the two different species from interbreeding (that breed with the other species). In brief, it preserves the integrity of the species by checking hybridization, they ensure that the different species will not breed. It may, however, be the origin of new species that occurs by the accumulation of the genetic variation in the population leads to evolution. There are many isolating mechanisms which leads to the barrier of the interbreeding species including:- geographical isolation, genetic isolation, ecological isolation, incompatibility, hybrid sterility, hybrid breakdown etc.
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