Sleep Habits

There have been many studies of the sleep patterns of animals both before and after the use of certain technology came about. Originally, scientists only studied animal sleep patterns in terms of how it applied to humans. Eventually, however, the animals were studied as themselves. Most of the animals that have been studied were mammals, including elephants, hedgehogs and whales. Reptiles, amphibians and other types of animals have also been studied.

A study of the evolution of sleep was conducted in the late 1960’s. They studied the sleep patterns of various types of animals, moving up the evolutionary scale. Here are some of the things that they found:

Salamanders and frogs are two animals early on in the evolutionary scale that are just past the development of land animals. The studies indicated that neither of these two animals really ever sleeps: they alternate between rest and activity.
The next step was to study reptiles such as turtles and snakes. Between this study and others done on reptilian sleep, many indecisive conclusions have been reached. Some people believe that reptiles simply rest as amphibians do. Others have decided that reptiles do through cycles in which they fall into a comatose state. This state is similar to the first stage of sleep in humans or the period just before sleep.
After reptiles, the study moved on to a group that is almost entirely extinct, called monotremes, which consists solely of the duckbill platypus and the echidna. These two animals are often instead grouped only with marsupials (which is valid). The echidna, which was the chosen animal for study, was found to actually sleep for 12 out of 24 each day. Although there was no indication of REM sleep at all, the sleep was equivalent to stages three and four of human sleep.
Next up on the revolutionary scale are the slightly more evolved marsupials, like the opossum. These marsupials were found to have sleep patterns with both deep sleep and REM sleep.
Primitive placental mammals were studied next and were found to have longer hours of sleep, about a quarter of which are REM. Along with the REM sleep, these animals were also found to have slow-wave sleep (stages three and four of human sleep).
Lastly, the study was done on quite a few higher mammals such as squirrels, cats, dogs, chimpanzees and donkeys. (Squirrels and cats were found to sleep about 14 hours a day, chimps 11, and donkeys only 4.) All of the animals studied in this category had advanced slow-wave sleep and REM sleep.
Birds follow a slightly different branch of evolutionary scale. They were, however, found to experience both deep sleep and REM sleep. Unlike even primitive mammals, birds had a very minimal amount of REM sleep.