Researchers recently discovered that animals developed the need to fall asleep, even before their brain was formed.
Who doesn’t love sleep? After a long hard day of work, studying, online classes, and working out, a good sleep on a comfortable mattress while snuggling under a blanket at the perfect room temperature seems like absolute heaven for many people. Sometimes, when you’re too exhausted even to think correctly, a 15-minute nap could do wonders, and those 15 minutes might seem like hours of blissful sleep. We’re usually told that an 8-hour sleep is good for the body, especially the brain.
However, a new Hamletian dilemma has arisen on what came first. No, we’re not talking about the chicken or the egg (according to science, the egg came first, since the first one was laid roughly around 312 million years ago. In comparison, chickens descended from their red junglefowl ancestors around 8000 years ago — so let’s put this debate to rest).
But this new paradoxical question is what came first — the brain or sleep? You can try your best to answer this without continuing further, but if you still want to know what the scientists have to say about this, read this article through till the end.
Sleep Precedes Brain
An international team of scientists discovered that hydras — a genus of small, fresh-water organisms that do not have any brains and nervous system, regularly engaged in sleep-like phases. They even lacked the necessary hormones and chemicals required to induce sleep in the higher order of animals yet seemed to enjoy a nap in the deep blue waters.
Previously, sleeping patterns were discovered in jellyfish too, which are biologically brainless. Hydras and jellyfish are members of the Phylum Cnidarians, whose signature feature is nematocysts’ (stinging cells) and tentacles. This recent study on hydra from the researchers at Kyushu University in Japan and Ulsan National Institute of Science and Technology in South Korea revealed that many biochemicals which induced sleep within humans had similar effects on the tiny hydras.
This study firmly supported that sleep is a quintessential part of animals even before they are mature. The reasons for its prominence over the brain’s development are still not known, but this could hold essential rationales to help us understand human evolution even deeper.
Sleep - A Result of Brain Waves
Hydras are obligatory aquatic animals which are 1-20 mm in size, big enough to be seen by a naked eye. They have 10-12 tentacles and a diverse network of nerves similar to a net. However, they don’t have a centralised nervous structure or even a recognisable brain, puzzling scientists more about the question discussed here.
As sleep is mostly monitored based on brain waves, researchers resorted to filming the delicate hydra using a video system to track its movement and determine when it entered sleep-like phases. It was confirmed with a reduction in the activity which could be disturbed with a flash of light.
HYDRA VULGARIS- the Experimental Subject
The hydra chosen were HYDRA VULGARIS. Rather than having the standard twenty-four-hour schedule resembling a circadian rhythm, to the researchers’ amazement, hydra’s exhibited a four-hour cycle of active phase and sleep-like phases. Even more, what baffled scientists is that regardless of the brains’ absence, several biochemicals involved in sleep and its regulation were found on the hydras’ molecular and genetic level.
After exposing the hydras to melatonin, a chemical in humans and other animals that bring about sleep and can be disrupted with blue light from screens, the hydras increased their sleeping time and frequency. The inhibitory neurotransmitter, called Gamma-Aminobutyric Acidy (GABA) observed the chemical in many animals to bring in sleep, and it profoundly affected hydras by lengthening their sleep phase.
Reverse Effects On Hydra
Interestingly, dopamine, a chemical that brings about excitement and stimulation in humans and other animals, didn’t do the same for the hydras. Instead, it promoted more sleep in it. Researchers used vibrations and temperature fluctuations to forcibly wake the hydras up and bring about signs of sleep deprivation. This led the hydras to fall asleep even longer the next day, and the animals even suspended their cell proliferation as they slept.
Furthermore, researchers discovered that sleep deprivation in hydras brought about changes in the expression of 212 genes, including one gene related to Protein Kinase CGMP-Dependent (PRKG), a type of protein which is involved in the regulation of sleep in many animals including mice, fruit flies, humans and nematodes.
Scientists Have a Say on their Discovery
Taichi Q. Itoh explained, “Based on our conclusions and previous reports regarding jellyfish, we can say that sleep evolution is free of brain evolution. Many issues remain regarding how sleep appeared in animals. Still, hydras provide an easy-to-handle being for further investigating the specific mechanisms producing sleep in brainless animals to help possibly one day explain these questions.”
While few sleep mechanisms appear to have been conserved, others may have changed capacity during the brain’s evolution. Taken all together, these experiments provide substantial evidence that creatures acquired sleep-related mechanisms before the evolutionaryry growth of the central nervous system and that many of these mechanisms were preserved as brains evolved.
The research has been published in the journal Proceedings of Science Advances.