Plant foods in human evolution: Factors affecting the harvest of nutrients from the floral environment

Informations projet

HARVEST

N° de convention de subvention: 677576

DOI

10.3030/677576

Projet clôturé

Date de signature de la CE 3 Mars 2016

Date de début 1 Février 2017

Date de fin 31 Octobre 2022

Financé au titre de

• EXCELLENT SCIENCE - European Research Council (ERC)

Coût total

€ 1 499 950,00

Contribution de l’UE

€ 1 499 950,00

Coordonné par

UNIVERSITEIT LEIDEN
Netherlands

Periodic Reporting for period 4 - HARVEST (Plant foods in human evolution: Factors affecting the harvest of nutrients from the floral environment)

Période du rapport: 2021-08-01 au 2022-10-31

Résumé du contexte et des objectifs généraux du projet

The choice of what to eat has never been more fraught, as people living today grapple with questions of personal health, environmental benefit, convenience of, and access to food. Some of our dietary choices are strongly influenced by our evolutionary history, namely the dietary decisions made by our ancient ancestors. By studying diets in the past, we can better understand the context in which our food choices are made today.

Ancient diets have been explored using a variety of methods, including querying the archaeological record, and studying recent historical and present-day foragers as analogues for the past. Much of scientific inquiry focuses on the role of meat in ancient societies. Animal-derived foods are often calorie dense, and those from large game are usually considered high-status foods. However, the potential role for plant foods in the ancient past remains under-explored. Plants comprise the majority of calories in most human diets today. They provide essential nutrients, including carbohydrates, fiber, and vitamins. We know relatively little about plant foods in ancient periods, in part because remains from plants are less likely to be preserved in the archaeological record, and in part because they are often considered of less value.

The HARVEST project elucidated the role of plant foods in ancient diets, as a key to understanding our present day dietary patterns. The objectives of this project included 1) reconstructing the plant component in the diets of fossil hominins, and 2) exploring the costs and benefits of plant foods. Foods are chosen in part for the nutrients they provide, but some foods may be overlooked because they require significant costs to be made edible. By looking at the chosen foods, and their costs and benefits we can explore the foraging goals of past populations; in other words, why our ancestors chose those foods.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

To explore diets in the past we focused on the analysis of dental calculus, or mineralized plaque. As it forms in the mouth over the lifetime of the individual, dental calculus traps markers of diet and behavior, including starch grains, proteins, lipids and DNA. It has proven to be a vital resource of dietary information, but it wasn’t clear how best to use this rare and limited archaeological material. Our early analysis proved it wasn’t possible to combine all the various analyses (e.g. starches and proteins and DNA) into one single “pipeline”. We therefore developed a lab-grown dental calculus that allowed us to test the effects of burial, changes in pH and other factors on the survival of starch grains. This new experimental system can provide other researchers a means to test the incorporation of various residues, and to see what methods are best adapted to extracting that information. Insights from these experiments allowed us to more carefully explore archaeological dental calculus samples, resulting in several high profile articles about, among others, the diets of the eastern-most Neanderthals.

To better understand the relative costs and benefits of consuming plant foods, we have pursued three areas of study: 1) Assessing variation in intrinsic nutritional properties to allow better predictions of past food choices, 2) exploring the factors that help determine food choices among a present-day hunter-gatherer group, and 3) accounting for the costs of cooking foods.

Many studies exploring the foods that our ancestors would have eaten in the deep past rely on previously published commercial literature, or on estimations for entire categories of foods based on single items. However, wild plants vary significantly between individuals, among habitats, seasonally, and from year to year in terms of their availability and nutritional properties. We have therefore collected better data on the nutritional and antifeedant properties of plants in several African environments that are similar to those used by our earliest ancestors. In contrast to expectations from previous studies, our results suggest that grasses were likely far more valuable, while plants growing in or near water were less nutritionally rich.

It often assumed in studies of human evolution that foragers choose the food that provides the greatest caloric benefit at the lowest cost. However, many other factors such as preferences and accessibility of food may also play a role. We have studied food decisions, energetics, and microbiome composition among the Baka forager/horticulturalists of Cameroon. During three field seasons, we collected a large variety of data using a novel combination of methods, including interview, observation, use of GPS and heart rate trackers. Our results suggest that this community considers both social influences and the energetic costs and benefits when choosing foods. Furthermore, gathering and agricultural work are the most energetically costly subsistence-related activities, but that the cost of gathering varies widely depending on the plant that is collected.

The benefits of fire for processing food have been well documented. However, the costs of fire have been largely ignored, despite the potential that they may have influenced when and how humans adopted fire use. We collected energetics data from three volunteers collecting firewood in three different habitats similar to those used by early European hominins. Fuel collecting in all three habitats was very energetically costly, and far outweighed the caloric benefit gained from cooking foods on those fires.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

Our analyses have provided an comprehensive data set that allows us to better understand both what plant foods our ancestors ate, but also why these foods were chosen. We have developed a new method that will refine our ability to see past use of plants, and to assess how reliable our reconstructions of the past are, both of which will increase confidence in this kind of analysis. Insights from the analysis of ancient calculus, and from studies of present-day peoples and environments all point to an important role of plants in the past, but one that varied significantly depending on the environmental context, and on individual decisions and societal pressures. The energetic and time costs of collecting and processing plant foods does impact when they are eaten, but these foods can have sufficient nutritional properties to justify their use. Unexpectedly, some foods that were long thought to be vital for our ancestors, such as those living in or near water, may not have been as nutritionally valuable. We also showed that the costs of cooking can be quite high, so when fuel is limited, some foods may not be eaten. The nutritional benefits of plants varies considerably between environments. In summary, a diet rich in plants, but varied in their use, is a hallmark of our species.

PI Amanda Henry observing starch grains at the microscope