Why do identical twins have different fingerprints?
The interesting thing about fingerprints...
Is that they have less to do with genetics (DNA) and more to do with the environment of the womb. Between 10 and 24 weeks, small ridges begin to form on the tips of the fingers and toes, and those are what eventually form into finger (and toe) prints.
The unique thing, is that although the DNA plays a part in having a likeness to mom and dad, most of what decides each unique print, is where the fetus is positioned, what the mother's diet consists of and how quickly baby develops. There are also other factors that can determine the unique formations of a person fingerprints, what can include any slight injuries to the fingers on the way out of the womb, or even thumb sucking during the time when the ridges along the fingers are developing.
The reason identical twins don't have identical fingerprints...
Is because once the egg separate and begin to form into individual fetus's, they've already begun their own lives. Because they came from the same egg from mom, they will forever have the same physical makeup, though after that anything can happen.
By the time they get between 10 and 24 weeks, when the ridges along the fingers start to form, they start out the same, but begin to change as the baby grows, mom's diet changes and they get more squished in the womb. It's similar to birthmarks, which often form individually as well.