Two sons were born to Eber: One was named Peleg, because in his time the earth was divided; his brother was named Joktan.
Genesis 10:25 (NIV)
Peleg means "divided."
Joktan means "to shrink."
The Rabbis note two things being said in Genesis 10:25:
1. This is when the confusion from the Tower of Babel occurred, and the world was divided afterwards.
2. The lifespan of humanity was cut short (to shrink) at this time.