Speaking of twins, there are actually a lot of discoveries where twins get separated, lived and grew in a completely different environment but end up having the same traits such as habits, ways of thinking, etc.

One of the most shocking findings is by Bouchard, Oskar and Jack ( http://www.psywww.com/intropsych/ch11_personality/bouchards_twin_research.html ):
1. Was raised in extremely different cultures; Oskar raised as Catholic; Jack as a Jew.
2. Both were wearing wire-rimmed glasses and mustaches.
3. Both sported two-pocket shirts with epaulets
4. They share idiosyncrasies galore.
5. They like spicy foods and sweet liqueurs, are absentminded
6. Have a habit of falling asleep in front of the television.
7. Think it's funny to sneeze in a crowd of strangers.
8. Flush the toilet before using it.
9. Read magazines from back to front. and many many more

Another shocking one (came from the same source) is the Jim Twins.
1. James Lewis and James Springer were separated weeks after birth.
2. Both married and divorced women named Linda.
3. Both had second marriages with women named Betty.
4. Both had police training and worked part-time with law enforcement agencies.
5. Both had childhood pets named Toy.
6. Their first-born sons were named James Alan Lewis and James Allan Springer.

Which brings the issue of 'Nature vs Nurture'. Are we really pre-programmed?