““The chemicals along a strand of DNA are arranged so that the molecule can make a copy of itself. Things being the way they are out there (or way down in there), these copies are not perfect. In the same way, you can tell the difference between an original document and a copy of the document made with a copy machine, it’s very difficult in nature to make a perfect copy. Those small changes in DNA that occur during an organism’s developmental stage result in the organism being just slightly different from its parents or parent organism.””
