[ELI5] Why can other species sleep with their heads up but we can’t?
In: Biology
It pretty much boils down to evolution. For tens of thousands of years, we haven’t had to worry about it as much with basic shelter building. Prey animals they been well getting preyed apon at night for maybe hundreds of thousands of years. We burn less energy not having to do that and therefore have an advantage in survival, given we are safe at night
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We can, and sleeping in a sitting position isn’t that rare. It’s just not as comfortable as sleeping in a bed.
Our brain prevents us from doing so. Look up images of decerebrate posturing.
A horse stands up and has its head up to sleep because its brainstem (primitive brain) has a code that makes its muscles in its arms and legs and neck extend.
Humans also have that primitive program encoded into their brainstem. Evolution of brains in mammals doesn’t take a lot of code away, it just writes new code on top of it. Your cerebral cortex, the top of your brain, has new code that is constantly overriding that horse-standupwhenyousleep program.
You don’t use it anymore because you’re a bipedal organism with 2 legs so why would you want a program that makes all 4 extremities extend. The primitive program can start running again when your cerebral cortex stops working due to severe brain damage.
REM sleep (at least for mammals, not a bird expert) still requires that the head be in contact with a hard surface for other animals due to the loss of muscle tone. Other animals make use of different sleep patterns so it’s easy to miss (REM sleep can be very short and broken up into several cycles).
Eg. horse REM sleep occurs in short periods (8-15 minutes frequently) in lateral recumbency, and their overall sleep for the day is broken up over several short sessions (often at night, but not always). If a horse is unable to lie down in lateral they cannot get REM sleep unless their head and body are supported in some other way (like a body sling with a cushioned head stand).
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