Excerpts from the Wikipedia pages on sleep. Most interesting I find the information on the human biological clock, and the hormonal and bodily effects it has. Habit and behaviour are but a small part in this.
Some of the many proposed functions of sleep:
- Memory processing
Sleep Needs for different age groups:
- Newborns (0–2 months) 12 to 18 hours
- Infants (3–11 months) 14 to 15 hours
- Toddlers (1–3 years) 12 to 14 hours
- Preschoolers (3–5 years) 11 to 13 hours
- School-age children (5–10 years) 10 to 11 hours
- Adolescents (10–17 years) 8.5 to 9.25 hours
- Adults, including elderly 7 to 9 hours
- Pregnant women 8(+) hours
Segmented sleep, also known as divided sleep, bimodal sleep pattern, or interrupted sleep, is a polyphasic or biphasic sleep pattern where two or more periods of sleep are punctuated by a period of wakefulness. Along with a nap (siesta) in the day, it has been argued that this is the natural pattern of human sleep. A case has been made that maintaining such a sleep pattern may be important in regulating stress.
Polyphasic sleep, a term coined by early 20th-century psychologist J.S. Szymanski, refers to the practice of sleeping multiple times in a 24-hour period—usually more than two, in contrast to biphasic sleep (twice per day) or monophasic sleep (once per day).
For more literature on sleep, see this post.