Natural selection is based on the idea that as an environment changes, an individual's genetic makeup will change suddenly to suit the new environment.

yes it is right because if we take example of viruses and germs ... new germs and viruses are much modified as compared to old ages because they adopted the ways they can escape from the immunity ... they have an adoption to transmit their DNA material, also they can take protein coat of host because of which host's immunity cells cannot recognize germs as foriegn particle ... and in this way germs and viruses remain for a long time in body due to the adoptations according to age and environment ...