 premature aging, growing a bark-like substance out of your skin or having facial hair like a werewolf. These are all examples of disorders suffered by some members of the human race and they are all due to genetic mutations. The one we grow and develop in the world is controlled by our DNA. Small sections of DNA called genes carry the code telling the body how to build itself. Usually this works fine but sometimes these genes carry mistakes in their code. These mistakes, known as mutations, may have no effect, they may be beneficial or they may be harmful. If the mutation is beneficial, the mutated individual will have a better chance of surviving and reproducing. With all the offspring benefiting of this mutation too, alternatively a harmful mutation means that that individual may not be able to survive and reproduce. As mutations in DNA are a random and ongoing process, non-beneficial and harmful genes are eventually weeded out of a population through a process called natural selection. Species evolve through a slow process of natural selection so that only the beneficial mutations are incorporated into a population whilst the harmful ones are removed. Sickle cell disease is an example of a genetic mutation that is harmful to humans. This mutation causes the hemoglobin molecules inside red blood cells to crystallize, meaning that instead of being a usual round shape, the red blood cells of sickle cell sufferers are an abnormal sickle-like shape. This makes it harder for these cells to carry on reduced oxygen. Individuals with sickle cell disease are at risk of a whole host of medical problems, such as heart attack and stroke. As recently as the 1970s, sickle cell sufferers did not live much beyond the age of 14, usually before they had a chance to reproduce and pose their defective genes to the next generation. I mentioned sickle cell as a choice example for a harmful mutation because, interestingly, it is involved in a beneficial mutation for immunity to malaria. Sickle cell carriers are more immune to malaria than those who aren't and are more likely to survive and reproduce, thus passing on the sickle cell trait. In this video you have learned that genes carry the code which tells our bodies how to develop and that sometimes this code changes and this process is called mutation. Mutations happen all the time, they can be beneficial, neutral or harmful in the effects. Over time and as a result of ongoing mutations, species evolve and change through natural selection.