Genetic diversity

If you think of a group of people in your street, or within your own family, no two will be exactly alike. All are humans, but all are different. These differences are due to genetic diversity, that is, the variety of genes within a species.

Each species consists of individuals with their own particular genetic composition. When the individuals interbreed, their offspring have new combinations of the genes, resulting in new mixtures of the characteristics of the species.

This diversity of characteristics is essential for the survival of healthy populations in natural communities. When the environment of a community changes, as they do all the time, some individuals will have characteristics that suit the new environment. They are more likely to survive and produce offspring that are also suited to the new environment. As a result, the whole population may change. This is how the process of adaptation occurs.

The story of the peppered moth (Biston betularia) provides a good example of a species adapting to changes in its environment. In pre-industrial England, almost all peppered moths were grey with dark flecks. However, there were also a few peppered moths that were black. During the day, moths rested on greyish, lichen-covered tree trunks. The grey peppered moths were well camouflaged on the grey trunks, but the black moths stood out and tended to get eaten by birds.

This situation was reversed by the industrial revolution in England. The pollution from factories killed the lichens on the tree trunks, leaving the dark bark exposed. With this change in the environment, the black moths were better camouflaged than the grey ones. Birds ate many more of the grey peppered moths, so most of the moths that survived to produce offspring were black. After many moth generations, almost all of the peppered moths in industrial areas were black. The species had changed to suit the new environment.

The peppered moths were able to adapt to environmental change because of their genetic diversity — there were genes for grey and also for black in the population. This is not always so.

If a small population of a species becomes isolated from the larger group, the small population is forced to reproduce by breeding within itself — to inbreed. Inbreeding can result in a loss of genetic diversity, making it harder for the species to adapt to changing conditions.

This has been the case with a group of Blanding's turtles in Kejimkujik National Park.

This loss of genetic diversity can eventually result in the extinction of the population.

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