It is literally a case study with a single pair of subjects. At first I thought the OP pop sci article was just focusing in on one pair of participants of many. Most of the discussions in threads here seem wholly unwarranted. There are loads of random factors that affect people’s development, many of which can’t realistically be measured in a study. Maybe one of them happened to become friends with with a classmate that’s really into literature and so they started reading a lot! Maybe they are both sensitive to sounds, but only one of them happens to live near an airport, disrupting their sleep at night.

It is not surprising that one particular set of monozygotic twins happens to markedly differ with respect to some traits. There are always outliers in large twin studies too, and researchers don’t usually get that hung up about them because everyone knows there are countless factors involved. To be able to have any certainty about the effects of a particular factor you need scale that lets you separate them from the random noise. It’s just basic statistics, like what is even anyone doing here. The study itself does make sense, but should be interpreted as extremely exploratory in nature, not something to draw any conclusions from. IMO the researchers themselves are irresponsible in this regard, as they speculate much more than what’s warranted in the discussion and conclusions sections. Like, one of their conclusions is “They [the twins] also show that cultural climates can modify values.”. First, that is something already widely known and accepted, but second and more importantly, that is not the kind of statement you should make based on a single pair of subjects.