Early-life disease exposure and associations with adult survival, cause of death, and reproductive success in preindustrial humans

Abstract

A leading hypothesis proposes that increased human life span since 1850 has resulted from decreased exposure to childhood infections, which has reduced chronic inflammation and later-life mortality rates, particularly from cardiovascular disease, stroke, and cancer. Early-life cohort mortality rate often predicts later-life survival in humans, but such associations could arise from factors other than disease exposure. Additionally, the impact of early-life disease exposure on reproduction remains unknown, and thus previous work ignores a major component of fitness through which selection acts upon life-history strategy. We collected data from seven 18th-and 19th-century Finnish populations experiencing naturally varying mortality and fertility levels. We quantified early-life disease exposure as the detrended child mortality rate from infectious diseases during an individual's first 5 y, controlling for important social factors. We found no support for an association between early-life disease exposure and all-cause mortality risk after age 15 or 50. We also found no link between early-life disease exposure and probability of death specifically from cardiovascular disease, stroke, or cancer. Independent of survival, there was no evidence to support associations between early-life disease exposure and any of several aspects of reproductive performance, including lifetime reproductive success and age at first birth, in either males or females. Our results do not support the prevailing assertion that exposure to infectious diseases in early life has long-lasting associations with later-life all-cause mortality risk or mortality putatively linked to chronic inflammation. Variation in adulthood conditions could therefore be the most likely source of recent increases in adult life span.inflammation | stress | infection | life history | fitness

Parasite‐associated mortality in a long‐lived mammal: Variation with host age, sex, and reproduction

“…Conflict, for example, can refer to known aggression from other animals as well as from conspecifics, “Stress” to mortality from taming attempts, and “Senescence” to deaths listed by veterinarians as “old age” in logbook entries, without more specific diagnosis (associated with general deterioration for elephants with a lifespan of 50–67 years). As such, our data are comparable to studies investigating historic causes of death in human populations, for example, from multigenerational parish records that are commonly used in epidemiological research (Hayward, Rickard, & Lummaa, ; Hayward, Rigby, & Lummaa, ), with the exception that in our study the causes of death were determined by trained health workers with long history of previous health of the animal in question. The MTE elephant population has not been subject to culling (Mar, ).…”

Prenatal loss of father during World War One is predictive of a reduced lifespan in adulthood

“…Indirect evidence against a significant early-mortality selection also comes from the examination of paternal occupations. The odds ratio of survival in the Finnish famine was ∼2.5 between rich and poor families (39). In contrast, we observed only minimal differences in the occupations of the fathers of the war orphans who survived to adulthood and the fathers of their MNOs (Table 1 and Table S1).…”

Sex differences in adult mortality rate mediated by early‐life environmental conditions

“…While infant survival rates are used within ecology as a proxy for the severity of environmental conditions, they can be simultaneously affected by a wide range of ecological factors including nutritional and abiotic stressors, as well as epidemics of infectious disease which were common at the time of our study population (Hayward et al . ) and were not incorporated into our study. It is likely that the factors determining infant survival rates differ greatly between our study population and current human populations, which could offer an explanation for the discrepancy between our results and modern trends.…”

“…Unpredictable climatic conditions led to frequent crop failures and, subsequently, famines and disease outbreaks were common (Hayward et al . , ). Environmental variation occurred throughout the study period, which we first quantify as variation in the infant survival rate, as previously used in a similar study in roe deer (Garratt et al .…”