New York based award-winning photographer Martin Schoeller, best known for his close-up portrait photography, recently completed a shoot for the cover story of the January 2012 issue of National Geographic magazine. Schoeller, whose celebrity portraits have graced the covers of more than 20 magazines, took on the subject of identical twins, capturing the subtle differences (or similarities?) between them.

The following excerpt comes from the January issue of National Geographic:

They have the same piercing eyes. The same color hair. One may be shy, while the other loves meeting new people. Discovering why identical twins differ-despite having the same DNA-could reveal a great deal about all of us.

… twin studies have helped lead scientists to a radical, almost heretical new conclusion: that nature and nurture are not the only elemental forces at work. According to a recent field called epigenetics, there is a third factor also in play, one that in some cases serves as a bridge between the environment and our genes, and in others operates on its own to shape who we are.

Marta (top); Emma (bottom) ? The 15-year-old sisters want to go to the same university and become opera singers. They both like to draw as well but have a different approach to their art. Marta depicts finely detailed faces, while Emma prefers more expansive images: the sky, the rain, objects in motion. (©Martin Schoeller/National Geographic)

Ramon (top); Eurides (bottom)  ? As infants, Ramon and Eurides looked so much alike that their mother gave them name bracelets so she wouldn't get confused and feed the same child twice. Today at age 34, the twins are next-door neighbors in Florida, living in identical custom-built houses. A topic of family debate: Who has the fullerface? Ramon says it's Eurides. Eurides (and the mother) say it's Ramon. Mom thinks it's because she mistakenly gave Eurides's portion to the other twin. (©Martin Schoeller/National Geographic)

Emily (top); Kate (bottom)  ? The nine-year-olds get along well and also have a psychic shopping bond. Their mom sometimes takes them to the mall on separate occasions. Even when one twin doesn't know what the other twin has selected, they typically want to buy the same clothes. (©Martin Schoeller/National Geographic)

Loretta (top); Lorraine (bottom)  ? When Loretta was diagnosed with breast cancer three years ago, Lorraine was in the doctor's office with her. Loretta asked if Lorraine should be checked as well. The doctor discovered that Lorraine also had breast cancer. After receiving treatment, the sisters are both in good health. (©Martin Schoeller/National Geographic)

Jeff (top); Steve (bottom)  ? In grade school it didn't matter that Jeff Nagel wasn't good at spelling-Steve was. The twins dressed identically save for wristwatches, which could be secretly switched before a test. Now 44, they work different jobs in Ohio but still fool people sometimes. Jeff, a chef, once asked Steve to lend a hand at a catering gig. The guests became so alarmed at how quickly Jeff moved in and out of the kitchen that they told him to slow down, not realizing more than one man was on the job. (©Martin Schoeller/National Geographic)

These photos and more are in the January 2012 issue of National Geographic magazine, on newsstands now.