The Photographic Fascination With Twins
"One of the photos that made photographer Diane Arbus famous was Identical Twins, Roselle, New Jersey, 
1967; it reverberated in The Shining and probably influenced Mary Ellen Mark's twin photos."
"It goes without saying that twins long have fascinated photographers — as well as scientists. How is it that identical twins with virtually identical DNA can be so different? Conversely, how is it that identical twins separated at birth can still have so much in common? An article in National Geographic's December issue explores the focus of recent research: How a third factor, beyond nature and nurture, might have a vital role in making us who we are. The term is epigenetics and the article explains it best."