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Ancient stone tools from China provide earliest evidence of rice harvesting

by Doreen Ware
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A new Dartmouth-led study analyzing stone tools from southern China provides the earliest evidence of rice harvesting, dating to as early as 10,000 years ago. The researchers identified two methods of harvesting rice, which helped initiate rice domestication. The results are published in PLOS ONE.

Wild rice is different from domesticated rice in several ways. Wild rice is often considered to be a more nutritious and flavorful option than domesticated rice, as it is richer in protein, fiber, vitamins, and minerals. Additionally, wild rice has a longer, more slender grain than domesticated rice, and it has a unique, nutty flavor that many people find appealing. Wild rice is also more expensive and less widely available than domesticated rice, which makes it a less popular choice for many people.

Wild rice naturally sheds ripe seeds, shattering them to the ground when they mature, while cultivated rice seeds stay on the plants when they mature. Shattering is the process by which wild rice sheds its ripe seeds, or “spikelets.” When the wild rice plant is ready to reproduce, it sends up long, slender stalks that bear small, oval-shaped seeds at the end. These seeds are enclosed in a protective casing called a “lemma,” which splits open when the seeds are ripe. The ripe seeds then fall into the water, where they will germinate and grow into new wild rice plants.

To harvest rice, some sort of tools would have been needed. In harvesting rice with tools, early rice cultivators were selecting the seeds that stay on the plants, so gradually the proportion of seeds that remain increased, resulting in domestication.

“For quite a long time, one of the puzzles has been that harvesting tools have not been found in southern China from the early Neolithic period or New Stone Age (10,000 — 7,000 Before Present) — the time period when we know rice began to be domesticated,” says lead author Jiajing Wang, an assistant professor of anthropology at Dartmouth. “However, when archaeologists were working at several early Neolithic sites in the Lower Yangtze River Valley, they found a lot of small pieces of stone, which had sharp edges that could have been used for harvesting plants.”

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“Our hypothesis was that maybe some of those small stone pieces were rice harvesting tools, which is what our results show.”

In the case of rice harvesting, people would use sharp-edged stone tools to cut the stalks of rice plants and collect the grains. These tools were likely similar to sickles, which are still used in some parts of the world for harvesting crops. However, the use of stone tools for rice harvesting is now rare, as more efficient and modern methods have been developed.

In the Lower Yangtze River Valley, the two earliest Neolithic culture groups were the Shangshan and Kuahuqiao.

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The researchers examined 52 flaked stone tools from the Shangshan and Hehuashan sites, the latter of which was occupied by Shangshan and Kuahuqiao cultures.

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The stone flakes are rough in appearance and are not finely made but have sharp edges. On average, the flaked tools are small enough to be held by one hand and measured approximately 1.7 inches in width and length. Stone flakes are small pieces of stone that have been shaped and sharpened by the process of flintknapping. Flintknapping is the ancient practice of using a hard, sharp stone to strike another stone, creating a sharp edge or point. This technique was used by early humans to make tools and weapons, such as knives, spears, and arrows. Stone flakes were created as a byproduct of flintknapping, and they were often sharp and jagged. These flakes were sometimes used as tools, but they were more often discarded or used as fuel for fires. Therefore, today, stone flakes are of interest to archaeologists and other researchers, who study them to learn more about the technologies and lifestyles of early humans.

To determine if the stone flakes were used for harvesting rice, the team conducted use-wear and phytolith residue analyses.

For the use-wear analysis, micro-scratches on the tools’ surfaces were examined under a microscope to determine how the stones were used. The results showed that 30 flakes have use-wear patterns similar to those produced by harvesting siliceous (silica-rich) plants, likely including rice.

Fine striations, high polish, and rounded edges distinguished the tools that were used for cutting plants from those that were used for processing hard materials, cutting animal tissues, and scraping wood.

Through the phytolith residue analysis, the researchers analyzed the microscopic residue left on the stone flakes known as “phytoliths” or silica skeleton of plants. They found that 28 of the tools contained rice phytoliths.

“What’s interesting about rice phytoliths is that rice husk and leaves produce different kinds of phytolith, which enabled us to determine how the rice was harvested,” says Wang.

The findings from the use-wear and phytolith analyses illustrated that two types of rice harvesting methods were used — “finger-knife” and “sickle” techniques. Both methods are still used in Asia today.

The stone flakes from the early phase (10,000 — 8,200 BP) showed that rice was largely harvested using the finger-knife method in which the panicles at the top of the rice plant are reaped. The results showed that the tools used for finger-knife harvesting had striations that were mainly perpendicular or diagonal to the edge of the stone flake, which suggests a cutting or scraping motion, and contained phytoliths from seeds or rice husk phytoliths, indicating that the rice was harvested from the top of the plant.

“A rice plant contains numerous panicles, which are clusters of flowers that contain the grains of rice. The panicles emerge from the plant’s stem and are typically found at the top of the plant. Each panicle can produce several hundred grains of rice, depending on the variety of rice and growing conditions. Panicles mature at different times, so the finger-knife harvesting technique is especially useful when rice domestication was in the early stage,” says Wang.

The stone flakes however, from the later phase (8,000 — 7,000 BP) had more evidence of sickle harvesting in which the lower part of the plant was harvested. These tools had striations that were predominantly parallel to the tool’s edge, reflecting that a slicing motion had likely been used.

Sickle harvesting is a method of harvesting crops, such as rice, using a curved blade called a sickle. The sickle is a handheld tool that is used to cut the crops at the base of the stem. It is a traditional method of harvesting that is still used in many parts of the world, particularly in regions where rice is a staple crop. Sickle harvesting is labor-intensive and can be physically demanding, but it is also a cost-effective and efficient way to harvest rice. It allows the farmer to quickly and easily cut the rice plants and collect the grains without damaging the plants or the grains.

“Sickle harvesting was more widely used when rice became more domesticated, and more ripe seeds stayed on the plant,” says Wang. “Since you are harvesting the entire plant at the same time, the rice leaves and stems could also be used for fuel, building materials, and other purposes, making this a much more effective harvesting method.”

Wang says, “Both harvesting methods would have reduced seed shattering. That’s why we think rice domestication was driven by human unconscious selection.”

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