This is the first in a series of posts reviewing the 17 articles found in the October 2014 Special Issue of American Journal of Botany, Speaking of Food: Connecting Basic and Applied Science.
Agricultural Origins from the Ground Up: Archaeological Approaches to Plant Domestication by BrieAnna S. Langlie, Natalie G. Mueller, Robert N. Spengler, and Gayle J. Fritz
Concern about food and the environment has been on the rise for a while now. Interest in healthy food grown and produced in a responsible manner has prompted people to investigate where their food is coming from. Archaeologists studying plant domestication and the rise of agriculture are also concerned with where our food came from; however, their research efforts are more focused on prehistoric events rather than on what is being stocked on today’s grocery store shelves.
The authors of this paper, all archaeologists specializing in paleoethnobotany or archaeobotany, offer a broad overview of the study of plant domestication and the emergence of agricultural economies. In their studies the authors “treat domestication as a process that originally preceded the formation of agricultural economies” and they define domestication as “genetic and morphological changes [in] a plant population in response to selective pressures imposed by cultivation.”
The first section of the paper explains why certain theoretical approaches to thinking about early plant domestication should be revised. These approaches include a centric view of plant domestication, single domestication trajectories, rapid pace plant domestication, and domestication being coupled with the development of agricultural economies.
The concept of centers of origin refers to specific regions in the world where the majority of crop domestication is thought to have occurred. Often these are regions where a high number of wild relatives of crops are found and where large civilizations emerged. But research has revealed numerous locations in various parts of the world where crop domestication occurred independently from traditional centers of origin leading archaeologists to further explore a noncentric view of domestication.
Related to the centers of origin debate is the single vs. multiple domestications debate. Single site domestication refers to a plant being domesticated in one location and then spread to other locations. Multiple site domestication refers to the same plant being domesticated in multiple sites independently. With the aid of genetic research, crops that were once thought to have been domesticated in a single region and then disseminated to other regions are now being shown to have multiple domestication sites. For example, it has been suggested that barley was domesticated independently in various locations, including the western Mediterranean region, Ethiopia, Morocco, and Tibet, as well as various parts of Southwest Asia.
Concerning the pace of crop domestication, “many scholars have presented evidence that domestication was slower and more gradual than previously envisioned” probably because the first domesticated crop plants were not “developed by plant breeders with clear end products in mind.” On this point, the authors conclude that debates over timelines are “likely to continue for some time,” and that “close communication between geneticists and archaeologists, including those with archaeobotanical expertise” will be necessary to tell the full story.
Domestication is typically viewed as a precursor to agriculture. But the authors point out that domestication occurred first and that agriculture did not immediately follow. To illustrate this point, they tell the story of the bottle gourd (Lagenaria siceraria), possibly the oldest domesticated plant. Native to Africa, the gourds likely floated across the Atlantic Ocean to the Americas (they also made their way to East Asia and other places) where they were domesticated multiple times by various groups of people at least 10,000 years ago. The gourds had numerous potential uses including containers, rattles, net floats, and even food (the young, immature fruits are edible). Large gourds with thick rinds were preferred by early humans, and the seeds of these were planted. The plants needed little attention, so caring for them did not mean having to adopt a sedentary lifestyle. The authors conclude that “although this example might seem peripheral to the development of serious food-producing economies or social complexity, it highlights early, intimate plant-people relationships and the abilities of people to modify their environments to enhance availability of desirable resources.”
Bottle gourds (Lagenaria siceraria) were possibly the earliest domesticated plant species (photo credit: www.eol.org)
In the next section of the paper, the authors discuss new and improved methods being used today to “address questions about the timing, scale, and causes of domestication.” Narrowing down the dates that plants were first domesticated is a major interest of archaeologists, and advances in radiocarbon dating have assisted in this quest. When DNA is being extracted, it is important to know the age of the material being analyzed in order to better reveal its history. Combining several methods for analyzing the data – especially as these methods are improved and new methods are developed – is crucial.
Advances in microscopy have helped to better analyze morphological changes in plants over time as well as to examine microfossils, like starch granules, pollen, and phytoliths (silica particles left behind after a plant decays). Observing phenotypic changes in fruits, seeds, and other plant parts and determining the presence of things like starch granules and pollen helps us to understand the pace and scope of domestication as well as to determine when certain domesticated plants were introduced to areas outside of their perceived center of origin. Advances in the science of taphonomy – “the study of decay processes following the death of an organism until it is fossilized or exhumed” – also aid researchers in better understanding the stories behind plant domestication.
Scanning electron microscope (SEM) image of pollen grains from common sunflower – Helianthus annuus (photo credit: wikimedia commons)
Working with experts in other areas of archaeology will also lead to greater understanding of plant domestication and the emergence of agricultural economies. The authors give examples of how studying human and animal bones can provide information about plant domestication and state that “other classes of archaeological data, such as household structure and storage features, agricultural and culinary tools, and soil morphology” will aid in better understanding “how and why domestication occurred as an historical and evolutionary process.”
Next the authors discuss anthropological views on the causes of plant domestication. One of the main debates among anthropologists when discussing agriculture is whether or not early humans were “pushed” or “pulled” into agricultural economies. Did increasing populations and/or decreasing availability of resources compel people to produce more of their own food or did human populations cultivate and domesticate plants in areas where resources were readily available, allowing them to live sedentary and stable existences? The authors conclude that “it is not necessary for one of these scenarios to explain all transitions to agriculture” as agriculture emerged independently in multiple locations around the globe, each time under its own specific set of circumstances.
The final section of the paper is a short discussion on the relatively under-researched topic of the diet and cuisine of ancient humans. Surely, a desire for particular foods and beverages lead to cultivation and domestication. The authors assert that “cuisines provide people with social identities, nationalism, spirituality, and a package of cognitive tools for coping with their environment. Without a doubt, culturally constructed food preferences played a role in the origins and spread of agriculture.”
This is a brief summary of a well-researched and detailed article concerning the fascinating topic of early plant domestication. Honestly, my synopsis hardly does it justice, so I urge you to read it for yourself if this topic interests you. I particularly appreciated the emphasis that the authors placed on using multiple methods and tools to collect and interpret data and how our perspectives should be revised as new and updated data emerge. The call for multiple disciplines to come together in collaboration to better understand the history of domestication and agriculture is also encouraging. In summation the authors state that “archaeological evidence indicates that every case of transition form hunter-gatherers to agricultural economies was unique … Identifying the specific nature of when, where, and how domestication occurred will undoubtedly elucidate how agriculture transformed the trajectory of human societies.”