Speaking of falling asleep, that’s one of the things we don’t understand very well. Sure, we know what happens when we sleep, such as the brain entering an alternative state, and muscles all relaxing, and we are being immobile and less “conscious” than when we are awake, but we don’t know why we do it. Sleep is generally broken up into non-REM sleep and REM sleep – Rapid Eye Movement.
When we fall asleep, we first enter non-REM sleep until we’re considered to be in deep sleep. We know this because heart rates dip, body temperature falls and the brain use the least amount of energy (and thus, has the least amount of activity). Then, between non-REM sleep periods, we enter, four to six periods of REM sleep per night (standard eight-hour sleep).
REM sleep is characterized by the rapid movement of the eyes behind our closed eyelids, a near complete loss of muscle tone (body going limp), and increased brain activity. It’s during REM sleep that we dream. REM sleep occurs in mammals and birds and is pretty unique across the vast breadth of life forms.
Sleep itself is not totally necessary for life. Jellyfish and other Cnidarians don’t sleep, and neither do bacteria, fungi, plants or sponges – at least not in any way that we’ve been able to notice. Plants do have circadian rhythms, though, i.e. they follow the earth day-night cycle and change biological processes to match.
This is why plants produce oxygen when there’s sunlight, but only produce carbon dioxide at night – they produce carbon dioxide all day, actually, but the net output is minuscule when compared to the oxygen they output during the day. It’s an old wives tale that you can be harmed if you sleep in a room full of plants at night because they will suck up all the oxygen.
They “breathe” such a little amount of oxygen, and let off so little CO2, that if you took a walk in a 300 square meter patch of trees, you’d be producing more CO2 than all of the trees put together!
There are several theories to try and explain why sleep evolved, or why it’s evolutionarily advantageous. For example, one school of thought is that sleep is the penalty for learning because all of what we learn is committed to long-term memory by way of our synapses forming new connections when we sleep, and perhaps purging useless information.
A simple suggestion is that it’s merely necessary in order to conserve energy and allow healing of muscles and tissues – a mandated rest period that’s essential for survival. The push-back on that is that nap makes us (and all mammals and birds) vulnerable to predators, and thus, it had to have a much bigger advantage in order for the trait to survive evolution.
Plus, why do we dream? And it’s not just humans who do it; if you’ve ever owned a pet dog or cat, you would have noticed them dreaming when they nap – sometimes even trying to run when asleep! What’s the advantage of dreaming?
There must be some advantage for it to survive natural selection. Not only do we have any idea why we sleep, but we also have no idea why we dream either.
Then there’s anesthesia, well, it’s a different from a nap in the sense that it’s a medically induced temporary coma, and there are no REM cycles. In fact, brain activity is more similar to a comatose patient than one who’s asleep.
The fact that the brain can enter that low level of activity because of medicines and almost always wake up again with no damage is phenomenal, but it also begs the question about why we didn’t evolve to reach such a deep level of sleep.
Was it only because of predators, or is there something different about us? Bears and hamsters and the like can enter a state similar to a coma called hibernation, in which they don’t REM sleep, but are in a much deeper state.
They wake up from this nap just as we awake from general anesthesia, except that they do it on their own in response to stimulus or changes in the environment.
So how come we never evolved to hibernate? Could we learn to do so? Questions abound, and concrete answers thus far have eluded us. It’s time to walk beyond the unknown, i.e. Lygometry!