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This article was published 22/1/2010 (3680 days ago), so information in it may no longer be current.
Sleep is a fundamental component of animal biology. New evidence confirms that, in humans, its timing reflects intelligence. People with higher IQs (intelligence quotients) tend to be more active nocturnally, going to bed later, whereas those with lower IQs usually retire to bed sooner after nightfall.
The precise function of sleep is arguable. But, accumulating evidence shows that lack of sleep in humans and animals can result in obesity, high blood pressure and reduced life spans. Drowsiness impairs mental performance. For instance, 37 per cent of all motor vehicle accidents are caused by drowsy motorists, according to a University of Pennsylvania study. Even minor sleep deficiencies impact on body chemistry.
According to Juliette Faraco of Stanford University, sleep loss generates a proportionate need for "sleep rebound".
One of the most controversial and significant recent findings is the correlation in humans between the earliness/lateness of sleep preferences and intelligence.
Robert Bolizs at Semmelweist University, and his coworkers, have shown that encephalograms during sleep illustrate how sleep elements are directly related to "wakeful cognitive performance." Studies by researchers H. Aliasson and colleagues show the timing of intervals of sleep "correlates closely" with student academic achievement.
Extensive research by Satoshi Kanazawa and colleagues at the London School of Economics and Political Science have uncovered significant differences in sleep-timing preferences among people, depending on their IQ scores.
People with higher IQs are more apt to be nocturnal night-owls. Those with lower IQs tend to restrict their activities primarily to daytime.
People who prefer to go to bed early, and who are early-risers, demonstrate "morningness," whereas those whose sleep patterns are shifted later demonstrate "eveningness." Researchers say eveningness tends to be a characteristic of those with higher IQs.
According to Kanazawa, ancestral humans were typically diurnal, and that a shift towards more nocturnal activities is an "evolutionarily novel preference" of the type normally found in more intelligent individuals, demonstrating "a higher level of cognitive complexity" in the practitioners.
Recent studies at the University of Bologna suggest early-risers are comparatively more conscientious people. Related studies indicate eveningness is often age-related and that eveningness usually peaks at between 17-21 years of age; thereafter morningness becomes more prevalent.
A 2008 study by psychologist Marina Giamnietro and colleagues indicates evening-types tend to be less reliable, less emotionally stable and more apt to suffer from depression, addictions and eating disorders.
Morningness or eveningness are often genetically-based, according to researchers Lambertus Klei at Carnegie Mellon Univesity, Patrick Rietz at the University of Pittsburgh and their associates. In 2008, studies at Max Planck Institute of Psychiatry demonstrated sleep-time preferences are often inherited, and subsequent data indicates that 50 per cent of sleep-time choices are dictated by genetic factors.
"Hypocretins" are inextricably linked to sleep/wakefulness, according to Stanford University research. Hypocretins react with "wake-up" cell groups, including dopamine.
Sleep parameters vary among animals. Cows, for instance, sleep open-eyed. Horses sleep standing up. Some birds can sleep in flight, others while standing. Dolphins sleep in one-half of their brain while the other half remains awake. Bats need 19.9 hours of sleep every 24 hours, lions need 13.5, rats 13, cats 12.5, whales 5.3, deer 3.1, giraffes 1.9, most birds three to eight and donkeys three.
Robert Alison has a PhD in zoology and is based in Victoria, B.C.