The best scientific answer to why we sleep - "Because we get sleepy?"

The multiple hypotheses proposed to explain the function of sleep reflect the incomplete understanding of the subject. (When asked, after 50 years of research, what he knew about the reason people sleep, William Dement, founder of Stanford University's Sleep Research Center, answered, "As far as I know, the only reason we need to sleep that is really, really solid is because we get sleepy.")[54] It is likely that sleep evolved to fulfill some primeval function and took on multiple functions over time[citation needed] (analogous to the larynx, which controls the passage of food and air, but descended over time to develop speech capabilities). @Curionic