Some comparative aspects of yawning in Betta splendens, Homo sapiens, Panthera leo, and Papio sphinx

Students of behavior have neglected yawning. It is rarely mentioned in animal behavior texts, and even books that would seem to be particularly relevant, such as Hinde's (1972) Non Verbal Communication, do not include yawning in the index. In physiology the standard texts such as Starlings Human Physiology (Davson & Eggleton, 1962) or the revised Johns Hopkins Atlas of Human Functional Anatomy (1977) devote only a few vague sentences to yawning, if it is mentioned at all. There is no precise knowledge of the eliciting stimuli, functions, development, or topography of yawning. Darwin (1873) described yawning in humans as an act of deep inspiration, followed by a lengthy, forceful expiration with simultaneous strong contraction of many skeletal muscle groups, and occasionally accompanied by lacrimation. Yawning is sometimes described as a reflex, and Moore (1942) reported that yawning is one of the first reflexes observed in newborn human infants. have all been suggested as stimuli for yawning. A widely held hypothesis is that oxygen insufficiency causes yawning, but Starlings Human Physiology does not mention this possibility, and Barbizet found the evidence for it to be inconclusive. Frequent or excessive yawning may accompany certain diseases of the central nervous system, particularly frontal lobe tumors and epidemic encephalitis, a contagious inflammation of the brain (Brock & Krieger, 1963). Gastric diseases, brain stem lesions, and certain varieties of epilepsy may also be accompanied by pathological yawning (Barbizet, 1958). On the other hand, Geigel, a Gerrnan physician, suggested that "a seriously sick person does not yawn, and when he does yawn again the danger is pasC (cited by Cramer, 1924). More recent research has indicated the involvement of a central cholinergic mechanism in the initiation of yawning by rats (Urba-Holmgren, Gonzalez, & Holmgren, 1977), with a positive modulating effect of serotonin (Urba-Holmgren, Holmgren, Rodriguez, & Gonzalez, 1979). Low doses of drugs that stimulate dopamine neurons also induce yawning in rats (Mogilnicka & Klimek, 1977). Injections into brain or cerebrospinal fluid of ACTH, melanocyte-stimulating hormone, or peptides having similar hormonal activity induce a stretching and yawning syndrome in several species. There is an association between yawning and some elements of sexual behavior (Huston, 197 1), and Phoenix and Chambers (1982) found that injections of testosterone produced yawning by male and female rhesus macaques. Holmgren, Urba-Holgrem, Aguilar, and Rodriguez (1980) found that testosterone treatment restored cholinomimetically induced yawning in castrated male rats and increased yawning in normal …