The researchers identified a sleep-like state in a tiny, brainless animal called a hydra. - Our brains need sleep to work properly. But it turns out you don't need a brain to sleep. In a new study, researchers identified a sleep-like state in a tiny, freshwater animal called a hydra, which has a simple anatomy and lacks a brain. "We now have strong evidence that animals must have acquired the need to sleep before acquiring a brain," study lead author Taichi Q. Itoh, an assistant professor at Kyushu University in Japan, said in a statement. The study, recently published in the journal Science Advances, has implications for our understanding of the reason the need for zzzs evolved.