Grace period of human mortality has declined for over a century

Human mortality is U-shaped and, therefore, defines an age $x^{*}$ separating lives with an overall negative net change in mortality from lives with an overall positive net change in mortality. How has age $x^{*}$ changed, also relatively to life expectancy, over recent human history? And how does $x^{*}$ compare between humans and other primates, the mortality of which is also U-shaped?

Modeling data from the Human Mortality Database, the historical change of $x^{*}$ in advanced economies is reported and compared with that of primates in wild and captive conditions the demography of which was already modeled in the literature.

In humans, a marked decline in $x^{*}$ for both sexes, also relatively to their life expectancy, is associated with medical and economic progress. Comparing wild with captive conditions in nonhuman primates, magnitude, and direction of the change in $x^{*}$ , both relatively to life expectancy and absolutely, can depend on genus and sex.

With medical and economic progress, human lives have transitioned from a negative to a positive net change in mortality independently of sex. There is no evidence of an analogous transition occurring in other primates when their environment is made more benign.