Blog 7 Selection vs Genetic Variation

Over the course of this semester we have examined the various forces that drive evolution. Selection is one such force, describing the increased likelihood of survival and reproduction in certain species that exists due to variances in genetic characteristics within a population. These genetic characteristics might serve to make an organism more desirable for mating and reproduction purposes, or better suited to the environment, making it more adept at competing for resources.

Given that this process curtails members of a population less fit to survive while encouraging the reproduction of members with a higher fitness level, one would think that selection would lead to the elimination of genetic variation over time. Yet, this theory does not translate into the real world as we don’t observe populations losing their genetic variation, even when highly advantageous mutations exist within a population and make it especially fit to thrive within its environment.

There are two reasons for this. One is that reproduction does not create offspring that are perfect genetic replicas of their parents. Since no sexually reproducing organism has a perfect method for passing on their genetic code, offspring will always vary from their parents in some fashion, meaning offspring will be born with mutations that differ from that of their parents. This influx of new mutations prevents the stagnation of genetic variation in a population and leads into the second reason that selection doesn’t result in the eradication of genetic variation over time.

The second reason for the continued genetic variation is actually the process of selection itself. This might register as strange, because how can selection serve to both reduce and foster genetic variation at the same time? This ties back into the previous paragraph, which describes the continuous introduction of new mutations into a population. As these mutations are introduced, some will be more conducive to the survival of an organism than others and thus become more heavily selected while the previously preferred mutations become less desirable in comparison. If offspring did not have mutations that differed from their parents, then genetic variation would lessen as selection came to emphasize the best mutations and remove the less desirable mutations from the population. However, since we do have this variety of mutations, selection actually promotes genetic diversity by instilling new mutations into the population with each generation of offspring.

Imperfect reproduction and the process of selection are both important mechanisms within evolution because of their role in genetic variation, which is vital to the survivability of a species. Without genetic variation, an organism would only be able to maximize its fitness to the extent that the best mutation within the population allowed. However, as the world changed and the organism encountered new obstacles, it would be unable to adapt to overcome them as the lack of genetic variation would leave it at a standstill, unable to evolve beyond the limits of the mutations already present within the population. This would leave the population incapable of competing with populations that do have genetic variation and the population lacking in genetic variation would eventually find itself extinct.