Marshall Brain's identical twin sons at birth Marshall Brain

You take it for granted that you are a totally unique person, different from everybody else on Earth. And you understand that everybody else is also unique.

On a most basic level, identical twins are fascinating because they challenge this truth. They are unique people, of course, but they're eerily like each other.



Consider the extreme case of the "Jim twins." Identical twins Jim Lewis and Jim Springer were only 4 weeks old when they were separated; each infant was taken in by a different adoptive family. At age 5, Lewis learned that he had a twin, but he said that the notion never truly "soaked in" until he was 38 years old. Springer learned of his twin sibling at age 8, but both he and his adoptive parents believed the sibling had died. The two were finally reunited at age 39. The similarities the twins shared not only amazed one another, but researchers at the University of Minnesota as well. The very fact that you had twin siblings separated at birth bearing the same name, both 6 feet tall and weighing exactly 180 pounds is pretty incredible. But there's more.

In her book "Entwined Lives," Nancy Segal lists the following shared characteristics:

As youngsters, each Jim had a dog named Toy.

Each Jim had been married two times — the first wives were both called Linda and the second wives were both called Betty.

One Jim had named his son James Allan and the other Jim had named his son James Alan.

Each twin had driven his light-blue Chevrolet to Pas Grille beach in Florida for family vacations.

Both Jims smoked Salem cigarettes and drank Miller Lite beer.

Both Jims had at one time held part-time posts as sheriffs.

Both were fingernail biters and suffered from migraine headaches.

Each Jim enjoyed leaving love notes to his wife throughout the house.

Of course, before you start thinking about science fiction movies with pod people, the Jims, like other identical twins, are not carbon copies of each other. Some obvious differences were discovered during their participation in the "Minnesota Study of Twins Reared Apart," including:

Each styled his hair differently; one Jim wore it combed straight, hanging down over his forehead (think Beatles circa 1961) and the other Jim wore it combed back and sported sideburns (think Johnny Cash circa 1957, but with longer 'burns).

One Jim more clearly conveyed himself through speech, while the other was better suited to writing.

While both Jims had been married twice, one Jim had taken vows with a third wife (called Sandy)

While not all as eerily similar as the Jim twins, many more instances of uncanny likenesses can be found among twins who were raised apart. The CBS news show "48 Hours" once interviewed five sets of identical twins who were raised apart, including the following:

Also known as the "giggle twins" (because they "laugh and fold their arms the same way"), Barbara Herbert and Daphne Goodship spent the first four decades of their lives apart. In the time following their reunion, they've discovered some remarkable parallels in their lives — both had miscarriages followed by the birth of two boys and then one girl.

Identical twins Tom Patterson and Steve Tazumi had very different upbringings. Raised in a Christian family by two janitors in rural Kansas, Tom still managed to choose the same career as his brother. Steve, who lives in Philadelphia, was raised in a Buddhist household. Both men own body building gyms.

Debbie Mehlman and Sharon Poset were also raised by families of different faiths. But nature versus nurture prevails in some interesting ways with these women. They both have the unusual habit of crossing their eyes when they get excited.

The Minnesota study even included a set of triplets. Although raised separately, Bobby Shafran, David Kellman and Eddy Galland shared similar personalities. According to the book "Entwined Lives," all were described as, "intelligent, extraverted and slightly rambunctious." Bobby and Eddy were the first to meet, reunited by one of Eddy's college friends. Upon seeing a newspaper photo of his brothers, David immediately contacted his siblings and the triplets were fully reunited.

It's obvious from these twins' stories that genetics are certainly a factor in shaping who we are. In the next section, we'll see how such close genetic matches actually form.