Mitchell has said of the book:
Literally all of the main characters, except one, are reincarnations of the same soul in different bodies throughout the novel identified by a birthmark...that's just a symbol really of the universality of human nature. The title itself "Cloud Atlas," the cloud refers to the ever changing manifestations of the Atlas, which is the fixed human nature which is always thus and ever shall be. So the book's theme is predacity, the way individuals prey on individuals, groups on groups, nations on nations, tribes on tribes. So I just take this theme and in a sense reincarnate that theme in another context...