While we all would like a good night’s sleep, some of us seem to need more than others. Experts agree that your average human adult needs between 7-9 hours of sleep a night to maintain a healthy immune system and funcitoning brain. We can go considerably longer without food than we can without sleep. Without food, we might get a little skinner. Without sleep, we die.
Adults over the age of 65 typically need between 7-8 hours of sleep a day, but they might not get it in one sitting, so to speak. They might only sleep intermittently at night and need frequent naps throughout the day. Newborns on the other hand need between 14-17 hours of sleep a day, as their bodies are busy building both physical and neurological infrastructures.
Children, in general, need more sleep than adults, and there is a brief period during puberty when teenagers can sleep up to 10 hours or so, but anything beyond that is just showing off.
Most living things on earth need some form of rest, and they vary greatly from species to species, mammal to fish to snails. When it comes to mammals, the amount of sleep a creature needs is a complicated equation of food source, metabolism, size, and brain activity. But we all need to sleep.
The largest land mammals such as Elephants and Giraffe can get by with only a few hours of sleep a day. Elephants have to eat almost continuously to maintain their massive size and so are constantly taking little naps. Giraffe, always on the lookout for predators, sleep less than two hours a day, and only in 5-15 minute increments. They are the true cat-nappers of the animal kingdom, because in reality cats only sleep about 12 hours a day, or half the time. We think of cats as constantly snoozing, but in the big scheme of things, they’re pretty active.
Bats are one of the sleepiest animals, waking for only about 4 hours a night to feed, then sleeping for the other 20 hours. At least once they’re awake, they’re especially active, able to eat their body weight in bugs in a single outing. For something that sleeps 20 hours a day, that's pretty efficient.
Even more drowsy than bats though is the Koala, which sleeps for about 22 hours or 91.7% of each day. They barely move when they are awake, so that is some slow metabolism. It was long believed that sloths were one of the more restful mammals sleeping between 16-20 hours a day in captivity, but in 2008, researchers were able to miniaturize neurophysiological recorders and discovered that in the wild, they only slept about 10 hours a day. Seems they are just like bored teenagers, if there’s nothing better to do, might as well catch some Z’s.
Some large herbivores, such as cows, spend much of their awake time in a state of drowsiness, which could explain why they only need about four hours of sleep. Apparently, this is why cows always look so dreamy. They’re rarely fully awake.
Fish don’t sleep, not the way we think of it, but they do rest. The myth that sharks never sleep is simply that, a myth. Even though they are the only fish with eyelids, which they use to protect their eyes when attacking, sharks go through periods of restful inactivity that helps them to restore brain function, but they keep their eyes open. Despite another myth, some sharks can remain motionless without drowning, due to special gills, but many do need to keep moving at all times.
One question a lot of people have, especially pet owners, is do animals dream? Research indicates that they do. The sleep of many animals can be broken down into two types REM and NREM. These stand for Rapid eye movement (REM), also known as active sleep or paradoxical sleep, and non-rapid eye movement (NREM), also known as quiet sleep.
The important thing here is that REM sleep, the period in which we dream, is characterized by a unique combination of high brain activity and an immobilized body. During the earliest phases of sleep, you may still be relatively alert. The brain produces what are known as beta waves, which are small and fast, but as your brain activity begins to slow down, slower waves known as alpha waves are produced.
During this time when you are not quite asleep, you may experience strange and extremely vivid sensations known as hypnagogic hallucinations. Common examples of this phenomenon include feeling like you are falling or hearing someone call your name.
Another very common event during this period is known as a myoclonic jerk. If you have ever startled suddenly for seemingly no reason at all, then you have experienced this phenomenon. While it might seem unusual, these myoclonic jerks are, in fact, quite common.
When they have tested rats, dogs, and cats, they found that many animals do in fact, enter REM sleep and exhibit brain activity similar to when they are active and awake, even though they appear to be asleep. So, what do tigers dream of, since it’s unlikely that it’s Halle Berry in her Cat Woman suit? Or to being it closer to home, what is your dog Rex dreaming of?
They are likely dreaming of the things they see and experience every day. Activities such as running and play, emotions such as fear and joy, as well as the people, places, and things they experience through their life.
If you’ve ever watched your dog twitch, mutter, or move their paw as if they are running, or chasing squirrels, you’ve probably wondered if they were dreaming. The short answer is yes. Are they dreaming about you? Also, yes. Could they be having a nightmare about the postman or that pesky squirrel? Yes and yes.
Humans sleep about in the middle of the pack of animal life on the planet. Some of us sleep more than others, some of us nap more frequently, but nothing on earth compares to the snail, which can snooze for up to three years. Three years!
In general, we don’t think a lot about the lives of snails, beyond them being hermaphrodites, which means they have both male and female reproductive organs. They have no sense of hearing, and salt is particularly detrimental. But what’s paricularly interesting is their ability to just shut down for extended periods, especially when conditions are less than ideal for them to survive.
Snails need moisture to survive, so if the weather is not cooperating, they can shift into a deep sleep similar to hibernation to escape. During this time, the snails will secrete mucus over their bodies to protect themselves from the dry, hot weather. It's not how most of us would choose to sleep, but hey.
Unlike humans, snails don’t abide by the arbitrary rules of night and day. Snails will sleep on and off in between periods of 13 to 15 hours. When they wake up though, they experience a sudden jolt of energy for the next 30 hours, where they get busy doing whatever it is that snails do, though "sudden jolt" is clearly a relative term.
While you contemplate what you might be able to accomplish were you to take a nap for the better part of a presidential term, or the average tenure of an NFL coach, here is a short, incomplete list of animals and how long they sleep:
- Horses – 2 hours
- Elephants – 3 hours
- Cows – 4 hours
- Giraffes – 4.5 hours
- Humans – 8 hours
- Rabbits – 8.5 hours
- Chimpanzees – 10 hours
- Red foxes – 10 hours
- Dogs – 10 hours
- House mice – 12.5 hours
- Cats – 12.5 hours
- Lions – 13.5 hours
- Platypuses – 14 hours
- Chipmunks – 15 hours
- Newborn Humans – 15 hours
- Giant armadillos – 18 hours
- Little brown bats – 20 hours