Fluctuating asymmetry (FA) is a measure of deviation from bilateral symmetry and has been shown to have a strong correlation with developmental instability. FA has also been associated with negative health outcomes and developmental disorders in humans. We postulated that development of maternal immunoreactivity to male fetuses would cause greater developmental instability in the later-born male fetuses. We expected the FA in males with older brothers to be greater than that of males without older brothers or females with or without older brothers. To test this hypothesis, we made six bilateral measurements of the hand and arm: hand width, hand length, length of the third proximal phalange, ulnar length, and the full length of the hand and arm. These measurements were then used to calculate the mean FA of study subjects, which included hospital inpatients and outpatients, visitors, and staff. A comparison of the mean asymmetries of the 77 males with older brothers, 88 males without older brothers, 123 females with older brothers, and 106 females without older brothers showed no significant difference between the four groups. Further studies should be performed to confirm our conclusion on maternal immunoreactivity and FA since this study included a limited number of morphological traits and relatively few male participants.
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