"The building of a connection between the Gompertz equation and the biology of ageing owes much to the work of biophysicist George Sacher [10] of the Argonne National Laboratory, whose introduction to ageing stemmed from the growing recognition during the 1950s that irradiation would shorten length of life [11]. The same recognition led physicist Leo Szilard [12] to propose the somatic mutation theory of ageing and prompted a range of studies on the effects of radiation on ageing both in animal models such as Drosophila (e.g. [13]) and also in human survivors of atomic bomb irradiation [14].

Sacher [10] used the Gompertz model to compare the patterns of increase in age-specific mortality rates across different species. By plotting age-specific mortality on a logarithmic scale against age (figure 1), he showed that a linear increase was generally observed, in accordance with the logarithmic version of equation (1.1), i.e.   

"Thomas B. L. Kirkwood, Decipherng death: a commentary on Gompertz (1825) 'On the nature of the function express of the law of human mortality and on a new mode of determining the value of life contingencies"). (http://rstb.royalsocietypublishing.org/content/370/1666/20140379,  accessed 01-2017