The Making of the Fittest by Sean B. Carroll was published in 2006, 14 years ago, but most of it is probably still correct.

The Making of the Fittest, DNA and the Ultimate Forensic Record of Evolution

Sean B. Carroll

According to Amazon, I purchased this book on August 18, 2007.

immortal genes, 35-36, 69-89, 81, 186-87

Immortal genes are one of the most interesting things about evolution. There is too much to copy from the book, but these are the ideas.

Natural selection also acts to remove, in Darwin's words, "injurious change".

The survival of individual genes over vast geological periods provides more than unimpeachable evidence of the preservative force of natural selection. They are clues to the history of life's evolution from ancient ancestors, a new kind of evidence that Darwin could never have imagined. I will show how these immortal genes are powerful genealogical records that reflect the degree of relatedness among kingdoms and help us retrieve and reconstruct events in the history of life that are not visible in the fossil record.

Immortal genes have survived not because they avoid mutation--they are as vulnerable to mutation as all other genes. The genes are immortal in the sense that the gene as a unit endures; however not every letter of the gene's code endures. This fact can be seen upon more detailed inspection of their DNA sequences and of the sequences of the proteins they encode, and it is a key demonstration of one aspect of the process of natural selection.

Realize that an immortal letter in a protein sequence has experienced mutation again and again, in uncountable numbers of individuals, in millions of species, over billions of years, but that all these mutations have been purged by selection over and over again.

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This blog has 429 posts about the evidence for evolution at evidence for evolution.