(CBS) 

If you can spot a child's future sexual orientation before the child even knows he or she has one, doesn't that prove it's genetic? Studies have shown that homosexuality runs in families. So genes must be the answer. But then the researchers tell you identical twins can have different sexual orientations.

60 Minutes found identical twins Steve and Greg Lofts in New York. They had the same upbringing, have the same DNA — and yet Greg is gay and Steve is straight.

When people meet the twins and find out one of them is gay, Greg says people have asked if he's sure, and how it can be. "Everyone is curious about that," he says.

There were signs, even when they were little kids. Their mother told Stahl that Steve loved sports and the outdoors while Greg liked helping out in the kitchen. But it wasn't until high school that Steve became convinced Greg was gay.

Asked if he said anything to his brother, Steve says, "I did actually. And I think the way I worded it was something like, 'You know, Greg, if you're gay, it's OK with me. And I'll still love you the same.' And he gave a very philosophical answer. He said something like, 'Well, I love the soul of a person and not the physical being.' And in my mind, I was like, 'Yep, he's gay.'"

"I wasn't ready just yet," Greg added.

Does this prove that it's not genetic?

"What it proves is it's not completely genetic. They have the same genes," says Bailey.

Asked if that brings us back to the mother and the father, Bailey says no.

"But that's environment," Stahl said.

"That's environment. But that's not the only environment. There's also the environment that happens to us while we’re in the womb. And scientists are realizing that environment is much more important than we ever thought it was," Bailey explained.

A newborn rat pup in the lab of Dr. Marc Breedlove at Michigan State University, may, oddly enough, hold important clues to what happens in the womb.

By Shari Finkelstein ©MMVI, CBS Broadcasting Inc. All Rights Reserved.

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