Before revision: This theory is strengthened by the fact that sleep is observed to be a necessary behavior across most of the animal kingdom, including some of the least evolved animals which have no need for other functions of sleep, such as memory consolidation or dreaming.
After revision: This theory is strengthened by the fact that sleep is observed to be a necessary behavior across most of the animal kingdom, including some of the least cognitively advanced animals which have no need for other functions of sleep, such as memory consolidation or dreaming.