Skip to main content

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

Periodic Reporting for period 3 - HARVEST (Plant foods in human evolution: Factors affecting the harvest of nutrients from the floral environment)

Reporting period: 2020-02-01 to 2021-07-31

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 will elucidate the role of plant foods in ancient diets, as a key to understanding our present day dietary patterns. The objectives of this project include 1) reconstructing the plant component in the diets of fossil hominins, and 2) exploring the costs and benefits of plant foods. These two research themes allow us to understand not only what our ancestors ate, but WHY those foods were chosen.
We identified five research programs (RP) to help us explore the two main research foci; two on the reconstruction of diet and three on exploring the costs and benefits of plant foods.

RP1a: Sequential Calculus Sampling
The number of studies using dental calculus to explore ancient human diet and behavior continues to grow, and more methods have been applied to archaeological specimens. We are creating a model dental calculus system, into which we can incorporate known amounts of starches or other residues. This has allowed us to perform controlled taphonomic experiments never before possible on ‘real’ calculus samples. We have build a variety of different model calculus trials and tested the effects of burial, changes in pH and other factors on the survival of starch grains.

RP1b: Applying the calculus pipeline to the fossil record
We have collected calculus samples from a variety of hominin samples spanning the globe. The further analysis of this material will proceed once the results of RP1a become clearer.

To better understand the relative costs and benefits of consuming plant foods, we have pursued three research programs that 1) assess variation in intrinsic plant properties to allow better predictions of hominin food choices, 2) explore the factors, including those intrinsic to the food and those specific to the forager, that help determine food choices among living foragers, and 3) account for the costs of applying thermal processing (fire) to foods.

Research Program 2a: Nutritional variability among African plants
Many studies exploring the foods that hominins 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 analogous to those used by early hominins. Preliminary work has emphasized the potential value of grasses for early hominins, and the large variation between habitats.

Research Program 2b: Foraging decisions and digestion
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, and collecting fecal and plaque samples for microbiome analyses. Our preliminary results suggests that both individual preference and the energetic costs and benefits of food are considered when foods are chosen. A more comprehensive analysis of this large body of complementary data is underway.

Research Program 2c: Costs of Fire:
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.
In addition to the scientific advances described above, we are strongly committed to sharing our results with the wider public.

We have prioritized engagement with the communities with whom we work. For example, the Baka have noted that their knowledge of traditional uses of wild resources is threatened by external factors, including increasing market integration, changing livelihood, and climate change. During our fieldwork, they expressed to us their desire to have this knowledge about wild plant foods be more widely recognized in local communities and international governments. We have therefore been working with them on a book about their knowledge of plants, including the local and scientific names, photos, and the uses of the plants. This book will be provided to the Baka, but also shared with the Cameroonian government, and with the wider scientific audience. Furthermore, in collaboration with a filmographer, we produced a movie for about the field work and the valorization of plant knowledge among the Baka.

We have reached out to the European public who fund our research, by producing a vlog about the the wild foods project. This vlog captured the daily experience of a the experimental archaeologist as he consumed only wild foods for a month. Furthermore, we have engaged a group of German highschool students in documenting of the visibility of wild plants throughout the year.

By the end of the project we hope to have provided new methodologies as well as a large volume of new data that will allow us to answer questions about the role of plant foods in ancient diets.
PI Amanda Henry observing starch grains at the microscope