Researchers identify plant cultivation in a 23,000-year-old site in the Galilee
The Middle East is called the "Cradle of Civilization" because it is where our hunter-gatherer ancestors first established sedentary farming communities. Recently, the traditional dating of humans' first agricultural attempt was shaken up by the discovery of the earliest-known example of plant cultivation in the Levant, 11,000 years earlier than previously accepted.
The team of archaeologists, botanists, and ecologists from Bar-Ilan University, Haifa University, Tel Aviv University, and Harvard University published their work in the scientific journal Plos One on July 22, 2015. The team's conclusions rest on three inter-connected findings, says the study's lead researcher, Prof. Ehud Weiss of Bar-Ilan University's Martin (Szusz) Department of Land of Israel Studies and Archaeology. First is the higher-than-usual presence at the site of domestic-type, rather than wild-type, wheat and barley dispersal units. Second, the researchers noted a high concentration of proto-weeds - plants of the type known to flourish in fields planted with domesticated crops. Finally, analysis of the tools found at the site revealed blades used for cutting and harvesting cereal plants.
First author is Dr. Ainit Snir, part of whose doctoral research - conducted in Prof. Weiss' lab - is included in the present study.
An Agricultural "Time Capsule" Hidden Under the Sea
The researchers' discovery was made at Ohalo II, a 23,000-year-old camp site of a community of hunter-gatherers that lived on the shore of the Sea of Galilee, Israel. The site is located 9 kilometers (5.5 miles) south of the modern city of Tiberias, and was discovered in 1989 when the level of the lake plummeted. The site was then excavated for six seasons by Prof. Dani Nadel from the Zinman Institute of Archaeology, the University of Haifa. Excavations at Ohalo II exposed six brush hut dwellings, a human grave, copious and well-preserved remains of both animal and plant foods, beads from the Mediterranean Sea, as well as evidence of flint tool manufacture and use.
According to Weiss, the study represents the earliest example of small-scale cultivation found anywhere in the world.
"The plant remains from the site were unusually well-preserved because of being charred and then covered by sediment and water which sealed them in low-oxygen conditions," Weiss explains. "Due to this, it was possible to recover an extensive amount of information on the site and its inhabitants - which made this a uniquely preserved site, and therefore one of the best archaeological examples worldwide of hunter-gatherers' way of life. Here we see evidence of repeated sowing and harvesting of later domesticated cereals."
From Plant Gathering to Flour Production
In the Ohalo II dwellings was a particularly rich assemblage of some 150,000 plant remains, showing that the site's residents gathered over 140 different plant species from the surrounding environment. Among these, Weiss's team identified edible cereals - such as wild emmer, wild barley, and wild oats. These cereals were mixed with 13 species of "proto-weeds" - ancient ancestors of the current weeds known to flourish in cultivated, single-crop fields - indicating that they grew and were subsequently unintentionally gathered together.
A grinding slab set firmly on a brush hut floor, a stone tool from which microscopic cereal starch granules were extracted, as well as a unique distribution pattern of seeds around this tool, provided additional, unequivocal evidence that cereal grains were brought into the hut and processed into flour. This flour was probably used to make dough, maybe by baking it on an installation of flat stones, found just outside one of the shelters.
Plants' Statistics Show Genetic Change Linked with Cultivation
Examination of the cereals found at the site shows an unusual percentage of domesticated-type, rather than wild-type, ear morphology. As Weiss explains, this change in the plant population is characteristic of a genetic mutation triggered when wild-type plants are sown repeatedly in cultivated fields.
"The ears of cereals like wheat and barley - in their wild form - are built from separate units that break off and are easily dispersed, allowing the seeds to reach the ground, germinate, and grow into a new plant without any human intervention," he says. "When humans cultivate these grains over a number of successive seasons, however, a change occurs. They develop a rough scar that locks the seed dispersal units together. Such plants cannot sow themselves. This is the hallmark of domesticated, rather than wild-type plants."
As part of Snir's thesis, Weiss and Snir undertook field tests around Israel, establishing that stands of wild-type barley are characterized by a low level of this rough-scar appearance - about 10% of the total population. The study of Ohalo II's plant remains, however, revealed a greatly-increased incidence of 36% mutated domestic-type disarticulation units - proving that planned cereal sowing and harvesting in this ancient community had been underway for years.
Tools for Harvesting
Another intriguing finding relates to a number of sickle blades - harvesting tools composed of sharp flint implements inserted in wood or bone handles - found at the site; these are among the oldest of their kind ever found.
"We found several sickle blades at Ohalo II, and the study under the microscope of the gloss along their cutting edge indicates that they were used for harvesting cereals just before their complete ripening," says Prof. Dani Nadel. "Analysis showed the presence of silicon, transferred from the wheat and barley plants at the time of cutting. This is another indication that the presence of a high percentage of domestic-type cereals was not random, but rather is a sign of the long-term cultivation practices of the site's residents."
Weeds and Planted Fields
When studying the plants found at Ohalo II, the researchers were surprised to find a large number of plants similar to weeds previously seen only 11,000 years later than Ohalo II, at the traditional date for the beginning of agriculture. Does this indicate that agriculture indeed began much earlier than historians, archaeologists and botanists have traditionally believed? Weiss says that the isolated example on the shores of the Sea of Galilee is an insufficient basis for such a claim.
"From what we see at Ohalo II, it is clear that cultivation occurred at this surprisingly early point in time, but we have no evidence that it continued in the region," Weiss says. "This is why we term our findings to be evidence of trial cultivation only. Moreover, since weeds are defined by botanists as plants that developed in response to human agriculture, we call the plants that share characteristics with weeds 'proto-weeds'."
A Trial that Preceded Later-Adopted Practice
Prof. Marcelo Sternberg, a co-author of the paper who is an ecologist at the Department of Molecular Biology and Ecology of Plants at Tel Aviv University, claims that the findings are exceptional. "We are witnessing the earliest trial of cultivation combined with land-use changes that led to the appearance of the earliest weeds. The findings are a clear indication of early human disturbance of the natural ecosystem."
Weiss agrees, adding that the current study provides reason to rethink our ancestors' abilities. "Even prior to full-scale cultivation, humans clearly had some basic knowledge of agriculture and even more importantly, exhibited foresight and planning," Weiss says. "The current research results from this site, situated in the cradle of ancient civilizations, show our ancestors were cleverer and more skilled than we had assumed. Although full-scale agriculture did not develop until much later, the attempt had already begun."
Paper co-author Prof. Ofer Bar-Yosef, a prehistorian from Harvard University's Department of Anthropology, notes that "the history of the evolution of technology is littered with new inventions that were either not accepted by their society or simply failed. An historical example is Leonardo da Vinci, who, in his notebooks, designed several flying machines during the early 15th century. Even though da Vinci was on the right track, we had to wait until the 19th century before the Wright brothers got their first plane off the ground."