Aging is common to all evolved species. However, in spite of being an universal process, different species can present different behaviors in their mortality curves [1]. Gompertz [2] was the first to report the exponential increase of the mortality with age in human populations; this behavior is present in most other species. Although, the death rates for some species are remarkable exceptions to this exponential behavior, especially at older ages, as reported for medflies and Drosophila [1].
Human mortalities are not expected to be same for all countries, at all times. Nevertheless, Azbel proposed a unitary law for mortality [3] after studying many mortality curves for humans from different countries and at different centuries. Azbel studied a region in the mortalities curves, where the logarithm of the death rate grows linearly with the age (ln(qx/b) = a + bx). Azbel reports that the parameters (a, b) from different mortality curves are correlated through a linear relation a = In A -bX and suggests that A and X are universal constants within the same species.
In this work, we check whether the Azbel findings are compatible with the mutation accumulation theory. We studied the time evolution of a same population but with different seeds in the random number generator of the bit-string model [4]. We found that the parameters of mortality curves obey the linear relation proposed by Azbel [5]. From our results and the Azbel's proposal, we were able to distinguish species (and simulate them) within the bit-string model framework. We reproduce the deviation of the exponential behavior in the death rates of heterogeneous populations. As far as we know, these are the first results for heterogeneous populations using this methodology.