New research links age-independent human mortality patterns to food production

The shift from hunting and gathering to agriculture in pre-colonial North America resulted in age-independent mortality, or changes in mortality caused by factors unrelated to age, according to a new study by a Penn State-led research team. The team found that the intensification of crop use occurred in two phases, the first resulting in a decline in age-specific mortality and the second associated with this increase. The study is the first to link mortality to food production regardless of age.

“This study speaks to our shared human experience,” said Penn State Distinguished Professor of Anthropology and lead author George Milner. “We have several examples around the world where we see the movement towards plant domestication as an independent event – eastern North America, particularly the middle of the continent, being one of them, but also the Fertile Crescent in the Middle East. . In addition, demographic changes are occurring. This article discusses the relationship between the agricultural transition and demographic changes.

The researchers examined previously published data to identify general trends in archaeobotanical samples, or plant remains from the archaeological record, and skeletal samples from sites in eight states stretching from Illinois to northern Alabama. They wanted to examine the relationship between crop domestication and an index that uses skeletal data to capture the frequency of juveniles between five and 19 years of age relative to all individuals aged five or older. Anthropologists typically use this indicator to measure fertility rates and population growth, but new work suggests it is more sensitive to age-independent mortality.

Mortality patterns, including those of pre-industrial societies, consist of three components: infant mortality, which declines as children age; adult mortality, where the probability of death increases with age; and age-independent mortality, equal probability of death for members of all age groups, which may occur during extreme events such as food shortages, epidemics, or wars.

The researchers examined archaeobotanical data to determine whether domesticated crops showed an increase in consumption relative to forage foods such as nuts. They also examined skeletal data to identify age-independent decreases or increases in mortality. The index focuses on individuals between the ages of five and 19, as this age group is characterized by lower mortality compared to other age groups in human populations. An increase in mortality for this age group indicates the occurrence of events such as famine or conflicts.

The researchers found a strong link between plant domestication and the evolution of age-independent mortality rates. Plant domestication occurred in pre-colonial North America in two phases, with an age-related decrease in mortality during the first phase of plant domestication and an increase in the second phase. The researchers published their findings Proceedings of the National Academy of Sciences.

“What we found is that the index, traditionally interpreted as an indicator of fertility and population growth, is more strongly associated with age-independent mortality, which reflects the number of deaths in the part of the age distribution where very few people die. ” says Milner. “This means that the pattern of early adoption of agriculture seen elsewhere in the world, and also seen in eastern North America, coincides with low mortality rates regardless of age.” Basically, it’s the right period and it’s what we see culturally. »

Milner said the first phase of agricultural intensification in North America, including the cultivation of pumpkins, sunflowers and other native plants, occurred during the Middle Woodland period, about 2,000 years ago. Local societies flourished during this period. They created long-distance trade networks, lived an incredibly rich ceremonial life, built large mounds and earthworks complexes.

The archaeological record shows that wars have increased in the centuries before 1000 and since. During this time, indigenous societies began to cultivate maize and beans, and a number of new cultural changes took place, including the initial development of powerful chiefdom societies. Age-independent mortality during this period likely increased due to conflict and the spread of disease from more individuals living in close proximity.

“The general pattern observed in the demographic chart of pre-European contact in North America is similar to other data sets around the world,” Milner said. “The whole story makes perfect sense in terms of agricultural productivity, demographic change and cultural development, as well as the evolution of conflicts and socio-political systems over time. »

According to Milner, the study is the first to link a global pattern of age-independent mortality and agricultural development.

“It’s a practical measure of what people eat, but also other aspects of society,” he said. “You cannot adopt a new technology without changing other aspects of society, such as the distribution of people and communities across the landscape. This agricultural event is a signal of other changes in society that we can measure or observe archaeologically. It’s really a bigger story about our common human experience. What we found in North America parallels the experiences of people in other parts of the world and reinforces that we are all in this together, no matter where we come from.

Jesper L. Boldsen, ADBOU, University of Southern Denmark, also contributed to the study.

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