Didn't geneticists also note that only a small fraction of our genetic code is actually in active useBack in the days when The Git was in Big School studying genetics nearly 50 years ago, it was clear there were two types of DNA. Only a small fraction was used to generate RNA, the rest was labelled "junk" DNA because it appeared to have no such function. Later, it was discovered that the "junk" was far better conserved than the useful stuff, so it was renamed "silent". Unravelling what DNA and replicated genes do and don't do is a matter of ongoing research.
In the meantime, the movement of genes between unrelated organisms was discovered. It would appear that horizontal/lateral gene transfer (HGT/LGT) plays a far more important role than point mutation of genes in situ. As an example there's a cnidarian (jellyfish) with perfect lenses, but lacking the necessary retina and brain to process visual information. Dawkins' account in The Blind Watchmaker has the retina and brain come before perfect lenses, not after.