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Birth data obtained from the parish records of the City of York, England show a markedly bi-modal seasonal distribution in the sixteenth century. It appeared interesting to compare the expectation of life of individuals born during this period, during the two minimal and two maximal seasons, to determine if there was any adaptive significance in the annual variation of birth rate. No such effect could be established by this study. However, certain conclusions of considerable interest can be drawn. The survivorship functions for either sex, grouped by birth season or on the whole group, are of a rectilinear diagonal type more reminiscent of an avian population rather than man. However the York data were treated, no statistically significant difference appeared between the sexes when their expectation of life was compared, and the female death rate at all times until the end of life was somewhat higher than the male. It appeared that sixteenth-century York tended to care better for their sons than for their daughters, which also appears to be the case in some modern societies of low to moderate living standard.