Four forces influence the process of evolution. These forces include natural selection, gene flow, mutation, and genetic drift. Each of these forces has an impact on variation within and between populations. Natural selection refers to the process by which best-suited individuals reproduce offsprings that guarantee their survival and existence. Parents pass on genes to offspring that give them a survival advantage over other individuals. Natural selection causes variation by propagating the inheritance of traits through successive generations. Natural selection has four main components that include variation, inheritance, population growth, and differential reproduction and survival of individuals. The variation takes place when a trait is inherited and passed on over different generations. Inherited traits are responsible for the survival of individuals because they give them an advantage over others. This way they reproduce and pass on good traits to their progenies and enhance survival. In this case, survival depends on the reproductive success of individuals. Gene flow refers to the carrying on of genes from one population to the other. Gene flow causes genetic variation if transported genes land in a population in which they did not exist before. This is because new genes are incorporated into a population that did not possess them. It mostly depends on the type of organisms that are involved in the exchange of genes. An example is a pollination in which pollen moves from one plant to another. Within a population, it can increase variation by introducing or reintroducing genes. Between populations, it can reduce the possibility of speciation because it makes different populations genetically similar. This encourages the propagation of that species by reproduction.
Mutation refers to the random alteration of the genetic composition of an organism. Mutations are random and bring variation to different aspects of an organism’s life. Evolution is because of the accumulation of mutations. Within and between populations, a beneficial mutation increases the reproductive ability of organisms. They also bring genetic variation by altering the genome of the organism’s DNA and this increases the chances of the mutation being carried over successive generations. Harmful mutations lower the chances of an organism’s survival. They render the progeny less able to adapt and survive when inherited from parents. Genetic drift refers to a change in the frequency with which a gene occurs in a population. This results from the fact that genes present in an offspring represent a random sample of the parent’s genes. Within populations, genetic drift decreases genetic variation due to a phenomenon known as a bottleneck. This happens when the size of a population decreases and so a certain gene may disappear from a population completely. Between populations, variation increases because the population is large and the chances of genes surviving are high.
An isolating mechanism is a factor that prevents different species from reproducing. They include genetic variations, behavioral, geographical, and morphological differences. These barriers lead to reproductive isolation that ensures that species remain different. Isolating mechanisms play an important role in the process of speciation. Speciation is a process through which new species come into existence. It arises from the prevention of gene flow between populations. Isolation mechanisms prevent the flow of genes between populations by creating productive barriers that lead to the emergence of new species. If different populations reproduce, then they belong to the same species. As such, their reproduction can never give rise to a new species.