Soybeans (Glycine max) - The Plant History of the Marvelous Soybean

Why Do Domestic Soybeans Have Half the Genetic Diversity of Wild Ones?

Grain Soybeans Ready to Harvest, Worthington, Minnesota, October 2013
Soybeans in a field are ready for harvest on October 2, 2013 near Worthington, Minnesota. Scott Olson / Getty Images News / Getty Images

Soybean (Glycine max) is believed to have been domesticated from its wild relative Glycine soja, in China between 6,000 and 9,000 years ago, although the specific region is unclear. The problem is, the current geographic range of wild soybeans is throughout East Asia and extending into neighboring regions such as the Russian far east, the Korean peninsula and Japan.

Scholars suggest that, as with many other domesticated plants, the process of soybean domestication was a slow one, perhaps taking place over a period of between 1,000-2,000 years.

Domesticated and Wild Traits

Wild soybeans grow in the form of creepers with many lateral branches, and it has a comparatively longer growing season than the domesticated version, flowering later than cultivated soybean. Wild soybean produces tiny black seeds rather than large yellow ones, and its pods shatter easily, promoting long distance seed dispersal, which farmers generally disapprove of. Domestic landraces are smaller, bushier plants with upright stems; cultivars such as that for edamame have erect and compact stem architecture, high harvest percentages and and high seed yield.

Other traits bred in by ancient farmers include pest and disease resistance, increased yield, improved quality, male sterility and fertility restoration; but wild beans are still more adaptive to a wider range of natural environments and are resistant to drought and salt stress.

History of Use and Development

To date, the earliest documented evidence for the use of Glycine of any kind comes from charred plant remains of wild soybean recovered from Jiahu in Henan province China, a Neolithic site occupied between 9000 and 7800 calendar years ago (cal bp).

DNA-based evidence for soybeans has been recovered from the early Jomon component levels of Sannai Maruyama, Japan (ca. 4800-3000 BC). Beans from Torihama in the Fukui prefecture of Japan were AMS dated to 5000 cal bp: those beans are plenty large enough to represent the domestic version.

The Middle Jomon [3000-2000 BC) site of Shimoyakebe had soybeans, one of which was AMS dated to between 4890-4960 cal BP.

It is considered domestic based on size; soybean impressions on Middle Jomon pots are also significantly larger than wild soybeans.

Bottlenecks and the Lack of Genetic Diversity

The genome of wild soybeans was reported in 2010 (Kim et al). While most scholars agree that DNA supports a single point of origin, the effect of that domestication has created some unusual characteristics. One readily visible, keen difference between wild and domestic soybean exists: the domestic version has about half the nucleotide diversity than that which is found in wild soybean--the percentage of loss varies from cultivar to cultivar.

A study published in 2015 (Zhao et al.) suggests that the genetic diversity was reduced by 37.5% in the early domestication process, and then another 8.3% in later genetic improvements. According to Guo et al., that might well have been related to Glycine spps ability to self-pollinate.

Historical Documentation

The earliest historical evidence for soybean use comes from Shang dynasty reports, written sometime between 1700-1100 BC. Whole beans were cooked or fermented into a paste and used in various dishes. By the Song Dynasty (960-1280 AD), soybeans had an explosion of uses; and in the 16th century AD, the beans spread throughout southeast Asia.

The first recorded soybean in Europe was in Carolus Linnaeus's Hortus Cliffortianus, compiled in 1737. Soybeans were first grown for ornamental purposes in England and France; in 1804 Yugoslavia, they were grown as a supplement in animal feed. The first documented use in the US was in 1765, in Georgia.

In 1917, it was discovered that heating soybean meal made it suitable as livestock feed, which led to the growth of the soybean processing industry. One of the American proponents was Henry Ford, who was interested in both nutritional and industrial use of soybeans. Soy was used to make plastic parts for Ford's Model T automobile. By the 1970s, the US supplied 2/3 of the world's soybeans, and in 2006, the US, Brazil and Argentina grew 81% of the world production. Most of the USA and Chinese crops are used domestically, those in South America are exported to China.

Modern Uses

Soybeans contain 18% oil and 38% protein: they are unique among plants in that they supply protein equal in quality to animal protein. Today, the main use (about 95%) is as edible oils with the rest for industrial products from cosmetics and hygiene products to paint removers and plastics. The high protein makes it useful for livestock and aquaculture feeds. A smaller percentage is used to make soy flour and protein for human consumption, and an even smaller percentage is used as edamame.

In Asia, soybeans are used in a variety of edible forms, including tofu, soymilk, tempeh, natto, soy sauce, bean sprouts, edamame and many others. The creation of cultivars continues, with new versions suitable for growing in different climates (Australia, Africa, Scandinavian countries) and or for developing different traits making soybean suitable for human use as grains or beans, animal consumption as forage or supplements, or industrial uses in the production of soy textiles and papers. Visit the SoyInfoCenter website to learn more about that.

Sources

This article is a part of the About.com guide to the Plant Domestication, and the Dictionary of Archaeology.

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