Was Sleep Inherited from Sponges? A Case for the Sleep Gene

Searching the internet, I was surprised to find that a solid case for the "sleep gene" hasn't yet been made.  Surely something as universal as sleep should be embedded in our genes somewhere.  A few months ago, researchers at the University of Tsukuba were able to isolate some genes in mice that are thought to be responsible for sleep.  The question becomes: since we evolved from rodents, might we also have sleep genes among the many sequences of our genome that haven't been examined yet?  The answer is probably yes. 

The reason we sleep might have to do with the genes we inherited from immobile organisms eons ago.  It's generally agreed that we evolved from fishes, that fishes evolved from flatworms, and that flatworms evolved from sponges.  Our ability to sleep may be genetically linked to these immobile sponges, which were among the first multi-cellular organisms that couldn't move.  Lifeforms that were even more primitive, such as the bacteria they evolved from, aren't known to have had the ability to sleep, suggesting that it's a phenomenon only associated with the animal kingdom. 

The ability of the first animals to move came as a result of convergence, which is a re-attainment of the genetic ability that a prior species on its genome had, activated after eons of dormancy.  In this case, the flatworms that evolved from sponges would have converged with the bacteria they'd evolved from, since bacteria was the only thing on its genome that could move on its own.  Furthermore, the fact that bacteria and other single-cell organisms don't sleep (or even rest) suggests that a metabolic change was imminent once the first immobile multi-cellular creatures came into existence. 

The ability for animals to sleep may also be convergent.  The part of the genome we inherited from sponges may have forced us to regain the metabolism necessary in order to perform functions our bodies couldn't do when awake, such as a resetting of the immune system and repairing tissue.  Our bodies would have learned these critical functions using the part of the genome that correlates with a lower sponge metabolism. 

Let's be clear though: sponges as we know them today don't sleep.  You need a nervous system in order to do that.  What's suggested here isn't an actual inheritance, but more of a way for animals to retain the benefits of a slow metabolism by using sleep as a model for immobility.  Regardless, there may have been a transition species of sponge that was able to sleep- a species that strongly resembled the worm it would evolve into.  Such a species of sponge in time would have had to develop a nervous system.  Where you draw the line between sponge and worm doesn't matter; in order to retain its balance, the worm had to rest the way its predecessor had. 

While worms also don't sleep the way we do, they certainly go through periods of rest, as do any other animal species that evolved from them, including arthropods.  The fact that virtually the entire animal kingdom performs some form of sleep means that it must have been inherited from a common ancestor.  That ancestor could only have been our friends from the deep, who rested on the ocean floor long before the first flatworms reared their tiny heads.  If it weren't for the sponge, our bodies might not have this otherwise magical ability to recharge itself during a nice, deep sleep.