via 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.
Every summer, on the first weekend in August, thousands of twins converge on Twinsburg, Ohio, a small town southeast of Cleveland named by identical twin brothers nearly two centuries ago.
They come, two by two, for the Twins Days Festival, a three-day marathon of picnics, talent shows, and look-alike contests that has grown into one of the world’s largest gatherings of twins.
The idea of using twins to measure the influence of heredity dates back to 1875, when the English scientist Francis Galton first suggested the approach (and coined the phrase “nature and nurture”). But twin studies took a surprising twist in the 1980s, following the discovery of numerous identical twins who’d been separated at birth.
The story began with the much publicized case of two brothers, both named Jim. Born in Piqua, Ohio, in 1939, Jim Springer and Jim Lewis were put up for adoption as babies and raised by different couples, who happened to give them the same first name. When Jim Springer reconnected with his brother at age 39 in 1979, they uncovered a string of other similarities and coincidences. Both men were six feet tall and weighed 180 pounds. Growing up, they’d both had dogs named Toy and taken family vacations in St. Pete Beach in Florida. As young men, they’d both married women named Linda, and then divorced them. Their second wives were both named Betty. They named their sons James Alan and James Allan. They’d both served as part-time sheriffs, enjoyed home carpentry projects, suffered severe headaches, smoked Salem cigarettes, and drank Miller Lite beer. Although they wore their hair differently—Jim Springer had bangs, while Jim Lewis combed his hair straight back—they had the same crooked smile, their voices were indistinguishable, and they both admitted to leaving love notes around the house for their wives.
On the interesting biochemistry of monozygotic twins.