Periodic Reporting for period 4 - HARVEST (Plant foods in human evolution: Factors affecting the harvest of nutrients from the floral environment)
Reporting period: 2021-08-01 to 2022-10-31
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.
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.