You'll find more about this topic on this site, but here's the nutshell bit.
Every time we see two things which are genetically identical, but which aren't the same, we're seeing epigenetics in action.
This affects huge amounts of life on earth and has a big impact on human health. The science is weird, heretical and fascinating.
I'm the author of The Epigenetics Revolution, a book aimed at a non-specialist readership, which discusses the amazing biology behind so much of life around us.