title: Season of birth, Geschwind and Galaburda hypothesis, and handedness.
abstract: Geschwind and Galaburda (1985a, 1985b) suggested that the season of conception is a non-genetic random variable that may affect laterality and handedness, probably due to seasonal variations in the hormonal influences on the foetal brain. According to this suggestion it is logical to expect seasonal anisotropy in the incidence of birth of right- and non-right-handers. The present study analysed data obtained from a sample of 3182 young Bulgarians: 2825 right-handers and 357 non-right-handers. Significant difference in the seasonal distribution of births of right- and non-right-handers was found in males only. The incidence of non-right-handedness was highest among participants born in winter. In right-handers increased birth rate was observed in spring and summer. The results in males seem to support the Geschwind and Galaburda suggestion. One can speculate that the high levels of mother's androgens during spring and early summer play the role of a "left shift" factor for the male foetuses with genetic potential for non-right-handedness.
authors.affiliation: Department of Physiology and Pathophysiology, Medical University Prof. Paraskev Stoyanov, Marin Drinov Str. 55, 9002 Varna, Bulgaria. zsd@mu-varna.bg
authors.forename: Zlatislav
authors.initials: Z
authors.lastname: Stoyanov
authors.forename: Piareta
authors.initials: P
authors.lastname: Nikolova
authors.forename: Irina
authors.initials: I
authors.lastname: Pashalieva
mesh_terms: D000293:Adolescent; D002031:Bulgaria; D004292:Dominance, Cerebral / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D009048:Motor Skills / Q000502:physiology*; D011247:Pregnancy; D012621:Seasons; D055815:Young Adult