This 2014 human study showed that DNA methylation was the most frequent way that duplicate genes were epigenetically silenced. Current thinking is that at least half of the genes in the human genome are inactive duplicates.
The study stated:
“Duplicate genes are essential and ongoing sources of genetic material.”
What the researchers didn’t show, however, was that duplicate genes evolve per the study’s title “evolution of duplicate genes.” It was misleading to imply in the study’s headline that duplicate genes evolve.
Evolution occurs as organisms adapt to their environments. Duplicate genes aren’t active in the adaptation process when they are silenced.
http://www.pnas.org/content/111/16/5932.full “DNA methylation and evolution of duplicate genes”