A new Dartmouth-led study that analyzes stone tools from southern China provides the earliest evidence of rice harvesting, dating back 10,000 years. Researchers have identified two methods of harvesting rice that helped kickstart rice domestication.Results published in PLOS.
Zizania is different from domesticated rice in that when it matures, it will naturally scatter mature seeds and crush them to the ground, while cultivated rice seeds remain on the plant when they mature.
To harvest rice, some kind of tool is needed. When harvesting rice with tools, early rice growers were selecting for the seeds that remained on the plant, thus gradually increasing the proportion of remaining seeds, leading to domestication.
“For a long time, one of the mysteries has been that no Early Neolithic or Neolithic (10,000 to 7,000 years ago) harvesting tools have been found in southern China — the period when we know rice began to be domesticated,” said lead author , said Wang Jiajing, an assistant professor of anthropology at Dartmouth University. “However, when archaeologists were working at several Early Neolithic sites in the lower Yangtze River Basin, they found many small stones with sharp edges that could be used to harvest plants.”
“Our hypothesis was that some of these small rocks might be rice harvesting tools, and that’s exactly what our results show.”
In the lower reaches of the Yangtze River, the two earliest Neolithic cultural groups were the Shangshan Culture and the Kuahuqiao Culture.
The researchers examined 52 sheet stone tools from the Shangshan and Hehuashan sites, the latter occupied by the Shangshan and Kuahuqiao cultures.
The stone flakes are rough in appearance and poor in workmanship, but with sharp edges and corners. On average, sheet tools are small enough to hold in one hand, about 1.7 inches wide and long.
To determine whether the stone flakes were used to harvest rice, the team performed use wear and phytolith residue analysis.
For in-use wear analysis, tool surfaces are examined under a microscope for micro-scratches to determine how the stone has been used. The results showed that the 30 flakes had usage wear patterns similar to flakes produced by harvesting siliceous (silicon dioxide-rich) plants, possibly including rice.
Fine stripes, high polish, and rounded edges distinguish tools for cutting plants from tools for working hard materials, cutting animal tissue, and scraping wood.
With phytolith residue analysis, the researchers analyzed the microscopic residue left on stone flakes known as “phytoliths,” or the plant’s silica skeleton. They found that 28 of these tools contained rice phytoliths.
“The interesting thing about rice phytoliths is that the husks and leaves produce different kinds of phytoliths, which allowed us to determine how the rice was harvested,” Wang said.
Results using attrition and phytolith analysis revealed that two rice harvesting methods were used – the ‘finger knife’ and ‘sickle’ techniques. Both methods are still used in Asia today.
Stone flakes from an early stage (10,000 – 8,200 BP) show that rice was harvested primarily using the finger knife method, ie harvesting the panicles at the top of the rice plants. The results showed that the finger knife harvesting tool had stripes mainly perpendicular or oblique to the edge of the stone flakes, indicating a cutting or scraping movement, and contained phytoliths from seeds or rice hull phytoliths, indicating that rice was harvested from the top of the plant .
“A rice plant contains many panicles that mature at different times, so the finger-knife harvesting technique was particularly useful in the early stages of rice domestication,” Wang said.
However, flakes from later stages (8,000 – 7,000 BP) have more evidence of sickle harvesting, in which the lower parts of the plant were harvested. The streaks of these tools are mainly parallel to the edges of the tool, reflecting the likely use of a slicing motion.
“When rice became more domesticated, sickle harvesting was more widely used, and more mature seeds were left on the plants,” Wang said. “Since the entire plant is harvested at the same time, the rice leaves and stems can also be used as fuel, construction material and other uses, making this harvesting method more efficient.”
“Both harvesting methods reduce seed breakage. That’s why we think rice domestication was driven by unconscious human selection,” Wang said.
