Research

Sleep is essential for surviving in all higher animals. Humans sleep approximately a third of their lifetime, and too little or too much sleep was often found to be associated with metabolic or psychiatric disorders. Sleep duration can be influenced by photoperiod and sleep time, and strongly depends on age and gender. However, a genetic component is also strongly suspected since twin studies indicate as much as 40% heritability in individual sleep duration.

Although their physiological role remains obscure, fingerprints (epidermal ridges) are characteristic of the human skin. They are widely used for identity check because their morphology remains permanent without any modification from their establishment at 24 weeks post-fertilization throughout lifespan.

Individuals completely missing fingerprints are extremely rare, but famous for encountering difficulties entering foreign countries. That is why their condition, scientifically termed adermatoglyphia, was surnamed the "immigration delay disease".