Identical twins share everything, genetically. The DNA of one is essentially a carbon copy of the other. They are always the same sex and they look, well, identical.
But identical twins, or twins born from a single fertilized egg that splits into two embryos, don't have the same fingerprints.
You see, even in a space as tiny as a womb, two distinct individuals have entirely separate experiences. They rub up against different parts of the uterine wall and bump into each other at different places on their bodies. Thus, each gets distinctive markings on his or her fingers.
It is variation in life experience, however, that makes them truly unique.
Fast forward 50 years, that's what Beijing-based photographer Gao Rungguo did.
Identical twins who start out looking very much alike don't always stay that way.
The color and texture of our individual experiences over the course of our lives, be they largely lucky or more challenging, shape us.
Perhaps nowhere is this more evident than in these simple, poignant photos of twins over the age of 50 in China's Shandong province.
Some of them look exactly alike, still.
And some, barely related.
The photographer, Gao Rungguo, cites St. Augustine on his website in the artist statement: "People born at the same time differ in temperament and fate."
Gao says he wanted to show how people who "used to have the same face and live in the same family" become dissimilar after growing up.
"Their lives changed for various reasons after growing up," he wrote.
Gao says he chose the age of 50 based on Confucius, who said that at the age of 50 one's fate becomes clear.
Hat tip, HuffPo.