1Type 2 diabetes is rapidly increasing in prevalence worldwide, in concert with epidemics of 2 obesity and sedentary behaviour that are themselves tracking economic development. 3Within this broad pattern, susceptibility to diabetes varies substantially in association with 4 ethnicity and nutritional exposures through the life-course. An evolutionary perspective may 5 help understand why humans are so prone to this condition in modern environments, and 6 why this risk is unequally distributed. A simple conceptual model treats diabetes risk as the 7 function of two interacting traits, namely 'metabolic capacity' which promotes glucose 8 homeostasis, and 'metabolic load' which challenges glucose homoeostasis. This conceptual 9 model helps understand how long-term and more recent trends in body composition can 10 then be considered to have shaped variability in diabetes risk. Hominin evolution appears to 11 have continued a broader trend evident in primates, towards lower levels of muscularity. In 12 addition, hominins developed higher levels of body fatness, especially in females in relative 13 terms. These traits most likely evolved as part of a broader reorganisation of human life 14 history traits in response to growing levels of ecological instability, enabling both survival 15 during tough periods and reproduction during bountiful periods. Since the emergence of 16Homo sapiens, populations have diverged in body composition in association with 17 geographical setting and local ecological stresses. These long-term trends in both metabolic 18 capacity and adiposity help explain the overall susceptibility of humans to diabetes in ways 19 that are similar to, and exacerbated by, the effects of nutritional exposures during the life-20 course. 21