The main message of the book is like sleep is sumer important, and we all need to be getting eight hours of sleep. Visit cultures that are untouched by electricity, and you often see something rather different. Hunter gatherer tribes, such as the gabra in northern kenya, or the and people in the kalahari desert, sleep in a biphasic pattern. Both these groups take a similarly longer sleep period at night, seven to eight hours time in bed,. achieving about seven hours of sleep, followed by a 30 to 60 minute nap in the afternoon.