A possible dependence of aging and life span in man on specific features of early ontogenesis has been analyzed on the basis of published and author's data. It was shown that the life span depended on climatic factors acting during prenatal and/or early postnatal period. When analyzing a sample of 101,634 humans died in Kiev in 1990-2000, a reliable relationship was established between the age of death and month of birth. The lowest and highest death ages were observed in persons born in April-June and in the end of the year, respectively. The lowest and highest average monthly values of death age differed in men and women by 2.6 and 2.3 years, respectively. In persons survived for more than 60 years, a "birthday" effect was demonstrated: dependence of the mortality level on the month of individual annual cycle was the highest in its first and last month. It has been proposed that this effect is related imprinting of the "birth stress" in the structure of biological rhythms, which may lead to periodic changes in viability during the individual annual cycle. The mechanisms underlying long-term effects of stresses in early ontogenesis have been studied on Drosophila melanogaster. X-irradiation of eggs at 0.50 and 0.75 Gy led to an increased level of survival of imago. The described radiation hormesis was accompanied by an increased resistance of DNA to S1-nuclease, which could be due to a long-term activation of the repair system in irradiated insects. The results obtained suggest that long-term changes in the range of gene expression induced by mild stresses in early ontogenesis can be a key mechanism of early "programming" of the potential of longevity and hormesis for life span.