Cell division is designed to follow a plan, a blueprint, a formula, all based upon information that is contained in DNA. Thus when a superficial skin cell dies it is replaced by one of the cells that have divided and formed in the basal layer of the epidermis. The entire top layer of the skin covering our bodies is replaced in this manner every 28 days.
If the DNA in a basal cell is transformed (undergoes mutation) by the effects of X-rays or ultraviolet rays, that cell begins to divide abnormally (chaotically) and it does not form normal skin. What does form is a basal cell or squamous cell skin cancer; or worse yet a deadly melanoma. The mutation has produced a growth that is either harmful or fatal to the person so afflicted.
When the cells that line our respiratory tract divide they normally form (replicate) other cells just like themselves. Those cells may become mucous producing structures that moisten and cleanse the air we breath. They cleanse by trapping dust and other particles on the sticky mucous so that they do not go deeper into our lungs. They may produce another kind of cells that have cilia (hair like projections) on the surface that sweep the dust laden mucous upward and outward from our lungs. On the other hand, if they are subjected to the hundreds of carcinogens contained in cigarette smoke and tar those cells may undergo DNA mutation and become one of several cancers. Once again a mutation has proven to be either harmful or fatal.
If a mother who is in her early stages of pregnancy (first trimester) contracts measles (Rubella) there is a 10 to 20% chance that her baby will be born with a developmental defect. That too is the result of a mutation which is in turn harmful to the newborn child through out his or her life.
Certain drugs are known to be teratogenic. That is, they are prone to produce congenital abnormalities, in the cardiovascular or neurological systems. Thus the caveats on drug labels that warn against taking them if one is pregnant. Radiologists and X-ray technicians are urged to wear badges that measure the accumulative effects of radiation in their bodies. That is because there is a high rate of leukemia in persons who are exposed to the ionizing radiation effects of X-rays and other radioactive materials. Those leukemias develop because of mutations and they are usually fatal.
Oncogenes are mutated genes that predispose to all sorts of cancers. People with oncogenes circulating in their blood streams may develop primary cancers in three or more organs, one after the other. Again, it is a result of mutations occurring in the DNA program.
If mutations in living humans are so detrimental to our well being, what kind of logic leads anyone to believe that we humans have evolved on planet earth, over billions of years, as a result of multiple mutations and natural selection? That is one of the basic, unproven, inane and illogical premises of macro evolution and that is what young people in our nations schools are being taught as a proven fact.