Mortality trajectories across demographic, economic and evolutionary response surfaces

We examine the mortality transition by placing country-specific trajectories on a landscape defined by demographic, social, and economic factors. We identify dimensions of a demographic ‘space’ that different countries have occupied through time. A population’s space is defined by life expectancy, GRR, latitude, and Gross Domestic Product per capita. We also quantify changes in the selection landscape by examining associations between mortality and Fisher’s reproductive value, Crow’s opportunity for selection, and Ryder’s demographic metabolism (the sum of the intrinsic birth and death rates). The large amounts of data (9 countries spanning 315 to 564 years) and the features of our demographic landscapes identify patterns among economic, selective, and historical factors that cannot typically be revealed in smaller scale analyses. For example, mortality reduction leads to changes in the relative variation of demographic traits, altering the potential for selection. We find that the potential for selection acting on longevity decreases dramatically as probability of survival to adulthood increases and that fertility selection is greatest when fertility is lowest. Likewise, countries often follow very different trajectories across the landscapes as they go through the mortality transition.