Sleep is a vital component of our health and well-being, and the same is true for nearly all other animals.
As we know, sleep is important for humans because it allows for growth, development, repair, and memory consolidation; experts theorize that animals have a similar need for sleep simply because they sleep even though it puts them in a vulnerable position—there must be a reason for it.
How Sleep Differs Across Animals
Sleep may be a nearly universal habit, but that doesn’t mean that all animals on the planet go about it the same way. Sleep can vary by species based on the amount of time spent asleep and how quickly someone cycles through the different sleep stages.
These discrepancies in sleep can highlight some interesting facts about animal species and how they differ from us.
Circadian Rhythms Across Species
Our circadian rhythm refers to the 24-hour internal clock that regulates the sleep-wake cycle. It is responsible for releasing certain hormones, such as melatonin, at key times in order to promote sleepiness or alertness. We’re not the only ones with a circadian rhythm, either.
Most animals have a natural circadian rhythm, but the timing of the circadian rhythm can differ by species.
Adult humans need, on average, 7 hours of sleep, and some animals need more sleep than humans while others need less. For instance, the three-toed sloth spends 70% of their time asleep (nearly 17 hours a day), while African elephants only sleep for an average of two hours a day.
The total amount of sleep is not the only factor that differs, either; while humans head toward monophasic sleep, with the occasional nap, as they age, animals often follow polyphasic sleep patterns where their sleep is divided into several periods of sleep during the day. For example, dogs can sleep up to 37% of the day, in addition to a long bout of sleep at night.
One area where we may differ, though, is in regard to circadian rhythm disruptions. Specifically, artificial light can cause our circadian rhythm to be thrown off, while animals, who spend all their time dictated by the sun, may find that their circadian rhythm remains regular. As a result, they may not struggle to fall asleep at night in the way that humans often do,
REM Sleep Differences
When we sleep, our body cycles through four different sleep stages; the first three are categorized as non-rapid eye movement (NREM) sleep, while the final stage is REM sleep. We’re not the only ones to have REM sleep, either. Many terrestrial mammals, including primates, experience REM sleep, although the amount of REM sleep differs based on the species. For instance, non-human primates may spend 5% of their time asleep in REM sleep, while elephants, who sleep for such a small amount of time, may not have REM sleep every day.
Not all animals experience REM sleep, either; dolphins and whales do not display the behaviors that we typically associate with REM sleep.
Our large percentage of REM sleep may be why we can get by on less sleep than other animals; the sleep that we get is of higher quality, so we don’t have to sleep as long.
Brain Activity While Sleeping
While we sleep, both halves of our brain go into rest mode, taking on tasks that are unique to sleep. However, not all animals share this trait. For example, dolphins appear to only have one hemisphere of their brain sleep at a time, and there’s an important purpose for this—the half that remains awake allows them to swim to the surface and breathe even while they’re sleeping.
Sleep Deprivation Causes Dysregulation in All
You know all too well how a night of poor sleep can make your next day more difficult. It’s common to experience impaired memory, mood changes, and illness without enough sleep, and the same is true for many animals. In fact, research has shown that sleep-deprived monkeys have elevated markers of immune activation and an impaired mood. This shows that sleep is important for all, no matter our species.
Sleep Disorders in Animals
We’re susceptible to sleep disorders, and so are animals. In fact, it is this connection that allows for many sleep studies to be completed that then provide insight into human sleep.
One sleep disorder that animals can also develop is narcolepsy, and studies into the sleep disorder in mice and dogs allowed researchers to identify a genetic mutation that is responsible for narcolepsy. The mutation destroys neurons that produce hypocretin, which is responsible for regulating wakefulness; these findings prompted research into the development of drugs that mimic hypocretin.
Sleep apnea is also a shared sleep disorder, and studies on sleep apnea in mice have allowed researchers to better understand how unconscious muscle control and obesity affect sleep apnea in all species, humans included.
Hibernation
As much as we may feel like hibernating in the winter months, that’s not something that we, as humans, do. However, the same is not true for many animals.
Hibernation is a sleep-like state that can last months, where an animal moves, eats, and produces waste very infrequently and only during brief periods of mild arousal. The purpose of hibernation is to conserve energy when there are severe temperature changes and food sources are scarce. Sometimes, animals must decide whether to hibernate or migrate.
Hibernation may not be something that humans do, but it is common to feel a dip in energy levels during the winter months.
Sleep Times
Compared to other primates, humans sleep the least in 24 hours, and humans pack a higher proportion of REM sleep into this shorter sleep duration. Researchers theorize that this may stem from the threats humans in the past faced, requiring them to spend less time in a vulnerable state of sleep.
Creating Sleep Spaces
Primates make nests, and humans make beds. Both species share the trait of having a designated place where they sleep, with these places promoting better sleep. However, most other animals do not have a designated place to sleep, so this is not a trait shared by all.
Comparing Sleep in Humans and Animals
Nearly all animals sleep, but we don’t all do it the same way. Our sleep times, sleep stages, and sleeping locations can all differ, but we also share a 24-hour circadian rhythm (even if it varies by species) and risk of certain sleep disorders, showing that even when we look different, sleep is one thing that can unite us all.