title: A review of the established and suspected causes of variations in human sex ratio at birth.
abstract: The human sex ratio (proportion male) at birth (SRB) varies with many variables. Some of this variation has an established proximate cause. For instance, low SRB (more females) at birth are associated with various forms of stressful events or circumstances during or prior to pregnancy. These low SRB are almost certainly mainly caused by maternal-stress-induced male foetal loss. Other types of SRB variation are thought to be caused by hormonal variation in either or both parents around the time of conception. One or other of these two types of proximate cause seems to be responsible for most of the established variation of SRB. This will be illustrated here in respect of some selected forms of SRB variation. It seems likely that a clarification of the hormonal causes of SRB variation will also help explain the striking (apparent) inconsistencies in the results of reported tests of the influential Trivers-Willard hypothesis. It is further proposed that an appreciation of the evidence that parental hormones influence SRB may enhance understanding of several important pathologies (hepatitis B, toxoplasmosis, testicular cancer, prostate cancer and autism).
authors.affiliation: The Galton Laboratory, Department of Genetics, Evolution and Environment, University College London, United Kingdom. Electronic address: w.james@ucl.ac.uk.
authors.forename: William H
authors.initials: WH
authors.lastname: James
authors.affiliation: Department of Paediatrics, Mater Dei Hospital Medical School, Malta. Electronic address: victor.e.grech@gov.mt.
authors.forename: Victor
authors.initials: V
authors.lastname: Grech
mesh_terms: D001722:Birth Order; D005260:Female; D046689:Fetal Mortality; D042341:Gonadal Hormones / Q000097:blood; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D012744:Sex Ratio; D013315:Stress, Psychological / Q000453:epidemiology
chemical_list: D042341:Gonadal Hormones