DEVELOPMENTAL STABILITY, EJACULATE SIZE, AND SPERM QUALITY IN MEN

There is accumulating evidence that women prefer symmetric men. This p reference would be adaptive if symmetry was correlated with a fitness trait such as fertility. We show that, in a sample of 53 men from an i nfertility clinic, a measure of overall absolute fluctuating asymmetry (FA) in digits 2 to 5 was negatively related to sperm number per ejac ulate, sperm speed, and sperm migration, and overall relative FA was n egatively related to sperm number and sperm speed. Subjects who had fe w or no sperm in their ejaculates (azoospermics) tended to have high F A, particularly when obstructive azoospermia was the likely diagnosis. Controlling for weight, height, and age left sperm number, sperm spee d, and sperm migration significantly related to both absolute and rela tive FA, The association between low digit FA and large ejaculates and high sperm quality may arise because (1) generalized developmental st ability of the body is related to fertility or (2) Hox genes control d ifferentiation of digits and the urinogenital system in vertebrates, a nd FA of the former is closely linked to developmental stability of th e latter. (C) 1998 Elsevier Science Inc.