 DNA mutation can be defined as permanent transmissible change in the genetic material. Either the genetic material may be DNA or RNA. So two things are important. One is the permanent change and the second one is that change should be transmitted to the next generation. If the change is not transmissible we cannot say it as a mutation. So in other words it is a permanent change in the nucleotide sequence of the genome of an organism. So if a change becomes a permanent component of the genome of an organism we can call that change as a mutation. DNA can be easily damaged even under normal physiological conditions. Many different kinds of chemical and physical agents can damage DNA. Some of these agents are endogenous while which are produced inside the cells as a result of normal metabolic pathways. So there may be some chemical it may be some other thing which is produced inside the cells and it damages the DNA. So these agents are called endogenous agents. While some other agents are exogenous which come from the surrounding environment. So it may get these agents may get entry from the environment into our body and then they reach to our cells and up to our DNA molecule. So some of these agents are exogenous which damage the DNA and some are endogenous. On one hand DNA stability is required to ensure that the genetic information may pass accurately from one generation to the next. It is also required for the correct functioning of the thousands of genes. You know there are thousands of genes and they are functioning and they will only function correctly if their sequence is correct. So DNA stability is required. On the other hand the genetic variation is needed to derive evolution. You know new organisms, new systems, new path ways are being evolved. So for this evolution genetic variation is required. If this variation would be lacking the new species including humans would have no horizon on this earth. So the life and biodiversity depend on a happy balance between DNA damage or DNA mutation and its repair. Both the things are very important.