0 Twin .. Full story

A twin is one of two offspring produced in the same pregnancy.
Twins can either be identical (in scientific usage, "monozygotic"), meaning that they develop from one zygote that splits and forms two embryos, or fraternal ("dizygotic") because they develop from two separate eggs that are fertilized by two separate sperm.

Chang and Eng Bunker,
born in Siam (now Thailand) in 1811,
were the origin of the term "Siamese twins".

In contrast, a fetus which develops alone in the womb is called a singleton, and the general term for one offspring of a multiple birth is multiple. It is theoretically possible for two singletons to be identical if all 23 chromosomes in both gametes from the mother and father were to be exact matches from one birth to the next. While this is statistically improbable (less than one in one billion-billion-billion chance) under natural conditions, a controlled pairing may someday be possible. A less complex way to engineer genetically identical offspring is through the process of cloning, a procedure that has successfully been accomplished with several species of mammals

twins: Statistics
twins: Zygosity
twins: Fraternal/Sororal (dizygotic) twins
twins: Identical (monozygotic) twins
twins: Genetic and epigenetic similarity
twins: Degree of separation
twins: Demographics
twins: Dtwins: elivery interval
twins: Complications of twin pregnancy
twins: Human twin studies

morre - http://en.wikipedia.org/wiki/Twin

Twin sisters from Powys are officially oldest in world

Two sisters who are 100 years old have been officially named as the oldest twins in the world.

Farmer's daughters Ena Pugh and Lily Millward, who still live in their own houses near Brecon, Powys, were given the title by Guinness World Records.

They were born on 4 January, 1910 when Queen Victoria's son Edward VII was king.

They have taken the record from two French sisters, Raymonde and Lucienne Wattelade, who are 98 years old.

The French twins said: "We think it's encouraging to know that there are older twins and are delighted to pass the record on to them."

bbc

See also
The World's Oldest Conjoined Twins
Strongest india baby : Conjoined Twins Gone Wrong
Conjoined twins born in China .. Twins Born with Two Heads on Single Body
The birth of two children stuck in a rare case in Yemen
Conjoined Twins : CONJOINED TWINS REUNITED AFTER SURGERY GOES AWRY
Les Twins Video & Photos 
funny Twin Baby .. videos