If something works better the odds are that it will replace the genes that are not as efficient. If it does not then the organism will be out competed and eventually the less efficient genes are lost. That is evolution. A positive change, that depends upon the environment.
Corruption of DNA code is not exclusively environmental
Where on earth did you get that from?
Even cancer research cannot explain why the corruption occurs in all cases. Yes sometimes it is environmental, such as smoking causing lung cancer, however many cancers have no apparent environmental cause...and to make your position even worse...some cancers are from problems in coding from previous generations that are also not shown to be caused by environmental factors.
For example, my mother had breast cancer, a close family friend had breast cancer, and my wife has had breast cancer, however, my wifes mom died of melanoma.
None of the above cancers are related to each other case.
My mother in laws case was absolutely environmental. However,
The breast cancer of my mother was estrogen-based and so was that of my wife. The professor who was involved in the research program my mother was part of after her treatment...which went on for a few years afterward, along with other researchers on the same medical panel studying breast cancer, all maintained that there was no specific environmental reason for her breast cancer. It was simply a failure with the information copying process, cells did not replicate exactly as it should and eventually something went wrong such that cancer started growing. The same appears to have been the case with my wife (although we are only going by what the oncologist and her specialist have said to us verbally).
Cancer is an example where I think your claim is false.
