Conjoined twins are extremely rare, and that’s part of what made me curious about their lives and experiences. In researching Gemini, I delved into biographies, memoirs, and other accounts of living as a conjoined twin, as well as gleaning what I could from accounts of living with other rare anatomies. There was medical research, too, of course, but what interested me most was the experiences of real people.

The basics: Conjoined twins are identical twins with connected bodies. They develop from a single fertilized egg that doesn’t separate fully. According to a CNN report, about 200 pairs of conjoined twins are born alive each year, and only about half of those survive until their first birthday.

Depending on where they’re conjoined, twins may be referred to as thoracopagus (joined at the chest), omphalopagus (joined at the trunk, usually the abdomen), pygopagus (joined at the buttocks), ischiopagus (joined at the hip), or craniopagus (joined at the head). In Gemini, Clara and Hailey are pygopagus twins.

Although many singletons imagine that conjoined twins would be miserable, the reality is that most adult conjoined twins have said that they’re happy to be conjoined and have no desire to be separated.

According to researcher Alice Domurat Dreger, “The fact is that across cultures and across time, the great majority of people who are conjoined simply have not expressed the sensation of being overly confined, horribly dependent, physically trapped, or unwillingly chained to others.”

Some online resources to learn more:

• Information about conjoined twins from the Children’s Hospital of Philadelphia, which has separated more than 20 pairs
• The Science of Conjoined Twins, a 5-minute video by National Geographic
• A 45-minute video documentary about conjoined twins Abigail and Brittany Hensel, filmed when they were in high school
• Famous conjoined twins throughout history
• Trailer for “Bound by Flesh,” a documentary about conjoined twins Daisy and Violet Hilton

For more in-depth background and discussions, some books that I found especially helpful in my research for Gemini are:

• One of Us: Conjoined Twins and the Future of Normal, by Alice Domurat Dreger
• The Lives and Loves of Daisy and Violet Hilton: A True Story of Conjoined Twins, by Dean Jensen
• Millie-Christine: Fearfully and Wonderfully Made, by Joanne Martell

More generally, on the topics of living with noticeable differences and navigating related questions of identity:

• Far From the Tree: Parents, Children, and the Search for Identity, by Andrew Solomon
• Autobiography of a Face, by Lucy Grealy