The dynamics of mortality of several generations of man, Wistar rats and line Canton-S fruit flies Drosophila melanogaster was investigated. The result was, that the correlation between sample mean and sample variance was negative for man, positive for flies and was absent for rats. To fit the survival curve we chose two-parametric Gompertz function. Starting from Strehler-Mildwan correlation (linear correlation between Gompertz function parameters), we obtained theoretical dependence between life-span mean and variance. This dependence had complex shape and points, corresponding to different species were situated at different segments of this curve that is corresponding to the various sign of correlation between these characteristics. Increasing of the mean man life-span attribute usually to advances in medicine and social environment. Associated with this the decreasing of the life-span variance, as it follows from this paper, depends on parameter point location on parametric plane, i.e. from biological feature of species.