George C. Williams have noted that people with systematically deficient responses to various adaptive phobias (e.g. basophobia, ophidiophobia, arachnophobia) are more temperamentally careless and more likely to receive unintentional injuries that are potentially fatal and have proposed that such deficient phobia should be classified as "hypophobia" due to its selfish genetic consequences. Elderly persons For a long time, the fear of falling was merely believed to be a result of the psychological trauma of a fall, also called "post-fall syndrome". This syndrome was first mentioned in 1982 by Murphy and Isaacs, who noticed that after a fall, ambulatory persons developed intense fear and walking disorders. Fear of falling has been identified as one of the key symptoms of this syndrome. Since that time, FOF has gained recognition as a specific health problem among older adults. However, FOF was also commonly found among elderly persons who had not yet experienced a fall. Prevalence of FOF appears to increase with age and to be higher in women. Age remains significant in multiple logistic regression analyses. The results of different studies have reported gender as a somewhat significant risk factor for fear of falling. Other risk factors of fear of falling in the elderly include dizziness, self-rated health status, depression, and problems with gait and balance. In animals Studies of nonhuman subjects support the theory that falling is an inborn fear. Gibson and Walk performed identical experiments with chicks, turtles, rats, kids, lambs, kittens, and puppies. The results were similar to those of the human infants, although each animal behaved a little differently according to the characteristics of its species. The chicks were tested less than 24 hours after hatching. It suggested that depth perception develops quickly in chickens, as the chicks never made the "mistake" of walking off the "deep" side of the cliff. The kids and lambs were also tested as soon as they could stand on their own. During the experiment, no goat or lamb ever stepped onto the glass of the deep side. When placed there, the animals displayed typical behavior by going into a posture of defense, with their front legs rigid and their back legs limp. In this state of immobility, the animals were pushed forward across the glass until their head and field of vision crossed the solid edge on the opposite side of the cliff; the goats and lambs would then relax and proceed to