User blog comment:D. Cello/Assassinews 02/16 -- AC3 date released/@comment-4524035-20120219220725/@comment-1153722-20120219223634

The whole concept of the games is that a single individual is reliving the memories of a single ancestor. There is no way that there would be two individuals reliving the memories of two of their ancestors who did the exact same things in their lives, let alone at the same time. While the concept of co-op is appealing to quite a large group of players, it is not possible for Assassin's Creed.