A research team has found evidence suggesting soybeans were cultivated in Japan about 5,000 years ago.
The team, which includes officials of Yamanashi Prefectural Museum of Art, announced recently traces of the nation’s oldest cultivated species of soybeans had been found in a clay pot excavated in Hokuto, Yamanashi Prefecture.
The pot, which dates back to the Jomon period (ca 10,000 B.C.-ca 300 B.C.), had a cavity on the tip of a fractured handle in which the researchers believe a soybean became embedded.
Traces of soybeans have previously been found in late Jomon period pottery dating back about 3,500 years that has been excavated in Kumamoto and other prefectures in Kyushu.
However, the pot excavated from Sakenomiba remains in Nagasakacho, Hokuto, in 1995, dates back a further 1,500 years.
“This finding shows that people living in the Jomon period had access to a greater variety of foods, by cultivating plants as well as hunting and foraging, than previously believed,” one researcher said.
A copy of the soybean trace was created using silicon resin through the so-called replica SEM method, after being examined with an electron microscope.
The researchers said the soybean was 11.9 millimeters long, 5.7 millimeters wide and 3.7 millimeters thick. Judging from the size and shape of the soybean, they believe it was a cultivated species.
(Yomiuri, Oct. 22, 2007)
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According to Origin, History and Uses of Soybean (Glycine Max) by Lance Gibson and Garren Benson, “The first domestication of soybean has been traced to the eastern half of North China in the eleventh century B.C. or perhaps a bit earlier.”
According to the ancient Chinese myth, in 2853 BCE, the legendary Emperor Shennong of China declared the five sacred plants to be: rice, wheat, barley, millet…and soybeans.
However, long before written records, soybeans were a crucial crop in eastern Asia, and soybean in China was used as a food and a component of drugs, 5,000 years ago. The wild ancestor of the soybean is Glycine soja (previously called G. ussuriensis), a legume native to central China. Wild-size soybeans have been found in the Yellow River basin of China. Today in China, soybean production is concentrated in Manchuria (Heilungkiang, Kirin, Liaoning) and Shantung. Soybeans are also grown extensively in the provinces of Anhwei, Honan, Hopei, Kansu, Kiangsu, Shansi, Shensi and Szechwan.
General literature and sources state that soybeans were introduced into several countries including Japan from about the first century CE to the Age of Discovery (15-16th century), due to the establishment of sea and land trade routes. The earliest Japanese textual reference to the soybean is in the classic Kojiki (Records of Ancient Matters), which was completed in 712 BC. Until the finds mentioned in the above news article, the best current evidence on the Japanese Archipelago suggested soybean cultivation occurred in the early Yayoi period. In the light of the new finds, soybean cultivation may have arrived in Japan earlier during the Jomon period or may even have been domesticated locally independent of Chinese sources, the finds are even earlier than those of Korea. Prior to fermented products such as soy sauce, tempeh, natto, and miso, soy was considered sacred for its use in crop rotation as a method of fixing nitrogen.
The oldest preserved soybeans found in archaeological sites in Korea dated about 1000 BCE, radiocarbon dating of soybean samples recovered through flotation during excavations at the Early Mumun period Okbang site in Korea indicated soybean was cultivated as a food crop in around 1000–900 BCE.
Soybeans remain a major crop in China, Japan, and Korea.
An important paper on Soybean domestication (subtitle “Does size matter?“) was published in November 2011 in PLOSone by G-A. Lee et al. According to the Archaeobotanist,
“This reports details on the morphometrics of more than 900 archaeological soybeans across 22 sites in (northern) China, South Korea and Japan, including 7 directly dated by AMS. This provides the first really good archaeological dataset for making inferences about soybean domestication, and includes a summary of the soybean metrics from Wangchenggang published in a Chinese monograph in 2007 by Zhao Zhijun (and in more detail his 2010 book collection) , previously suggested to indicate some size increase by the Longshan period (i.e. 2500-1900 BC). The data reported here suggests large, truly domesticated soybeans present in middle Jomon Japan Shimoyakebe (near Tokyo), from the Third Millennium BC. These are significantly larger than those from the Yellow River valley of similar age, the Longshan period, which are also probably enlarged by selection under cultivation (at least the population from Wangchengang appear enlarged while some other Longshan samples still fall in the wild type range). In Korea a measured population form the Middle Chulmun is perhaps marginally enlarged while those of the later Mumum had clearly undergone selection for size increase. The overall impression that selection for seed size increase in soybeans was a protracted process and one that was uneven in different regions, and it may be that in some areas wild population continued to be exploited or proximity of wild populations and early cultivation methods did not lends themselves to selecting for larger seed size. This then complements data emerging from several crops for a protracted process of evolution of domestication traits (see previous, for example my articles in Annals of Botany or Evolution, and for a discussion of protracted domestication processes in the New World tropics see the recent Current Anthropology by Piperno). It also strongly points to a Jomon domestication independent from that in northern China, and one in which seed size evolved more quickly.”
Sources and readings:
“Soybean find suggests 5,000 year cultivation”, Yomiuri, Oct. 22, 2007
The Archaeobotanist | “Soybean archaeobotany: multiple origins and not coincident with cereals” (6 Dec, 2011)
M. M. Lager, The Useful Soybean (1945); J. P. Houck et al., Soybeans and Their Products (1972).
A Special Report on History of Soybeans and Soyfoods in China and Around the World | A Chapter from the Unpublished Manuscript, History of Soybeans and Soyfoods: 1100 B.C. to the 1980s by William Shurtleff and Akiko Aoyagi Retr. from Soyinfocenter.com
On the domestication of the Soybean (National Soybean Research Laboratory)
Heritage of Japan 
Very informative and helpful. Many thanks!