Originally Posted by AlienQ

As Dundes points out in support of this theory, evil eye belief is geographically spread out in a radiating ring from ancient Sumer, where it apparently got its start. It is mentioned the Torah (the Old Testament of the Bible) and its existence is acknowledged by modern Arabs, Jews, and Christians.

The evil eye is the name for a sickness transmitted -- usually without intention -- by someone who is envious, jealous, or covetous. It is also called the invidious eye and the envious eye. In Hebrew it is ayin ha'ra (the evil eye), which in Yiddish is variously spelled ayin horoh, ayin hora, or ayen hara. In mainland Italian it is mal occhio (the bad eye) and in Spanish mal ojo or el ojo (the bad eye or just the eye). In Sicily it is jettatore (the projection [from the eye]) and in Farsi it is bla band (the eye of evil).

There is nothing exclusively Jewish about the hamesh hand. Arab cultures often refer to it as the Hand of Fatima, which represents the Hand of G-d. Similar designs are common in many cultures. Why it has become such a popular symbol among Jews? I haven't been able to find an adequate explanation anywhere. My best guess: in many cultures, this hand pattern represents a protection against the evil eye, and the evil eye has historically been a popular superstition among Jews.