The classic example discussed is a study of children born during a famine. Children born during famine are going to be smaller than normal, but it was found that their children and grandchildren would be born smaller than normal, even though the famine has long since passed. This change has been attributed to a particular methylation pattern that was passed down.
It's known that things like exposure to famine and abuse can change methylation patterns, but this study suggests that non-traumatic things like your cultural upbringing can affect methylation.
It seems like the debate we're having is a rehash of nature vs nurture, where it seems like the new research indicates nurture can affect nature for future generations through gene expression.
“These data suggest that the interplay between race and ethnicity as social constructs and genetic ancestry as a biological construct is more complex than we had realized,” said Noah Zaitlen, PhD, a UCSF assistant professor of medicine and co-senior author on the new study. “In a medical context both elements may provide valuable information.”
Setting aside the fact that this is such a touchy issue that the authors are carefully couching their language, it looks like there may be ways in which this new information can help people by tailoring medical treatments. I'd love a ELI5 explanation of this if I'm somehow misunderstanding, but the conclusion I formed seems to be supported by the article to my reading of it.
Note, I'm not taking a hardline stance. That's why I said "race is not just a social construct" in my conclusion.