Humans and other animals must have a certain number of hours of sleep to survive. Scientists study sleep with am Electroencephalograph which measures and records electrical waves from the brain. The Brain of an awake yet relaxed person gives off about 10 small waves per second and as the person starts to sleep the waves grow larger and are slower. Since some people s jobs are at night some sleep during the daytime. Sleeping patterns develop gradually.
Babies usually sleep for brief periods throughout the day.
Only reptiles, birds and mammals really sleep. Most reptiles do not have sleep periods. Birds have very brief sleep periods. Mammals have periods of dreaming sleep and slow- wave sleep. Some mammals such as cattle sleep standing up, but can only dream while lying down.