I am a sucker for reports on research using identical twins subjects. Observing the physical and psychological similarities and differences are the way we get closest to teasing apart those two great forces that shape who we are as humans: nature and nurture.

So I listened carefully to the recent NPR report featuring adult identical twins who, from birth, were among a dozen or so identical siblings in a study that would never, ever be allowed today. The repercussions are huge, the study design unimaginable, and, practically most conflicting of all, the notes and information and possible results of the study are stuffed away in a file cabinet somewhere.

The doctor behind the study is still alive, by the way. And unapologetic.

Okay, the study: Paula Bernstein and Elyse Schein were both born in New York City. Both women were adopted as infants and raised by loving families. They met for the first time when they were 35 years old, shortly after they had found they were "identical strangers." These two shared a womb, and even played together until they were four or so months old, while being observed by psychologists and doctors who took part in this study.

The sisters were intentionally adopted to separate families. Neither girl grew up knowing she had an identical twin. Schein first learned she was a twin while searching for information about her biological mother.* Sometime later, Berstein got a call from the adoption agency who informed her she was a twin and her twin sister's name.

The two have written a memoir “Identical Strangers” about their lives, their reunion, the fallout of the study, and meeting the doctor in charge. The sisters say they have a close relationship. They can’t imagine how the study got approved, yet still can’t imagine not having the lives they had.

Some of the other identical siblings in the study – also raised separately – have reunited as well. But four of the subjects likely still have no idea they may have an identical sibling out there.

Their story is a great listen – the radio interviewer talks to the doctor! – and likely a great read (there's an excerpt on the NPR site). 

More recent laws in New York state require siblings be adopted out together.* 

* Corrected. A previous version said that new state laws in New York require adoptions records to be open to adoptees. That is incorrect.