title: The origins of fluctuations in the human secondary sex ratio.
mesh_terms: D003075:Coitus; D005260:Female; D005306:Fertilization; D006801:Humans; D008297:Male; D008954:Models, Biological; D011247:Pregnancy; D011336:Probability; D012744:Sex Ratio; D013081:Sperm Motility; D013094:Spermatozoa; D014429:Twins, Dizygotic; D014960:X Chromosome; D014998:Y Chromosome