Throw all the seeds into the water, and you will know which one is left by the ancients.

In 2016, archaeologists discovered a large number of carbonized wheat grains in an ash pit used for landfill when excavating the Haojing site of the Western Zhou Dynasty in Xi'an, which shows that my country had already begun to grow wheat on a large scale in the middle of the Western Zhou Dynasty.

Previous theories believed that wheat was not planted on a large scale until the Han Dynasty. The archaeological discoveries at the Haojing site in Xi'an have challenged this traditional view. However, such discoveries require more than just the well-known "archaeology".

Carbonized wheat particles unearthed from the Haojing site in Xi'an | news.cctv

A discipline that studies how ancient people cultivated land

You may wonder how these inconspicuous wheat grains were picked out of the loess? This has to mention "archaeobotany", a discipline that focuses on the interaction between ancient human civilization and unearthed plants. Plant samples provide direct evidence of the lives of ancient people, showing how they cultivated and ate plants, and also allowing us to see the co-evolution of humans and plants.

However, it is extremely difficult for archaeological botanists to find these plant samples in the ruins and use them to study ancient human civilization.

First, plant samples are difficult to preserve. Instead, they are easily corrupted by microbial activity, so only under very special conditions can they withstand the erosion of time and wait to be discovered by modern archaeologists. Among them, the most common preservation mode is carbonization.

Carbonized barley grain under a microscope | Cmhenkel / Wikimedia Commons

When plant seeds are exposed to fire in a low-oxygen environment, such as when ancient humans accidentally burned plant seeds, they develop a carbonized shell that protects them from microorganisms and the acid and alkali in the soil. Other modes of preservation include saturation (isolated by water in environments such as lake bottoms), dehydration (in environments such as deserts), mineralization (the conversion of organic matter into inorganic matter due to microbial or environmental influences), and so on.

Even if they are lucky enough to survive to this day, it is still difficult to pick out these seeds from the soil. Early archaeologists found some plant seeds basically by luck. In the 1960s, the flotation method came into being. Since the specific gravity of seeds is lighter than water and soil, the carbonized seeds can be screened out through buoyancy.

Left: Drying of heavy residues after water flotation; Right: Sorting of dried heavy residues by eye | Louis-Léopold Boilly / Wikimedia Commons

This method can systematically find plant seeds in the soil, which are much more numerous and diverse than those picked by hand. By classifying and counting these seeds, researchers can have a clearer understanding of the lives of ancient humans. For example, the proportion of weed seeds can reflect the function of the site; while the proportion of crop seeds can show the complete diet of ancient humans.

In addition to seeds and leaves, which are visible to the naked eye, archaeological remains may also contain pollen, starch, and other "small remains" that can only be seen with a microscope. For example, starch grains may be found in pottery jars used to hold food or on stone mills used to grind flour, and starch grains from different plants will show unique morphological characteristics under a microscope.

Cross-extinction image of a plant starch granule | The McCrone Group

Gradually "doubling" wheat

As the staple food of people in most parts of the world, wheat has been unearthed in a wide range of places around the world. By dating and testing the genes of wheat excavated from archaeological excavations in different regions, researchers can gradually draw a map of the spread of wheat.

The first diploid wheat domesticated by humans was called Emmer wheat, and its relative, Urartu wheat, hybridized with a similar species of Aegilops spp. to produce tetraploid Emmer wheat. Emmer and Emmer wheat were domesticated by humans in the Fertile Crescent around 10,000 BC.

The "ancestors" of domesticated wheat: Einkorn (left) and Emmer (right) | Left: Kurt Stueber / Wikimedia Commons; Right: Robert Flogaus-Faust / Wikimedia Commons

The biggest difference between wild and domesticated wheat is whether the cob to which the grains are attached is fragile. The cobs of wild one-kernel wheat and two-kernel wheat become brittle after the grains mature, allowing the seeds to fall to the ground naturally. This helps spread the seeds in the wild, but it is not very convenient for humans who collect wheat grains. Therefore, genetic mutations that make the cobs less fragile have been favored by humans, and humans will help these mutants that have difficulty surviving in the wild to sow. In 2017, after sequencing the genotypes of wild and domesticated wheat, people found two important genetic mutations related to this trait.

Domesticated wheat has a less brittle cob when mature | Roger Culos / Wikimedia Commons

Emmer wheat later spread to Greece, Cyprus, Egypt, Spain and Germany, and became one of the important staple foods in Egypt. It is now sold in the market as a healthy food.

About 8,000 years ago, cultivated emmer wheat accidentally hybridized with wild Aegilops tauschii (also known as rough goat grass) in the Caspian Sea coast from Transcaucasus to northern Iran, eventually forming hexaploid common wheat. Currently, the earliest hexaploid wheat confirmed by DNA analysis is about 6400-6200 BC and was found in Catalùk, Turkey.

Çatalhöyük is a large Neolithic and Chalcolithic settlement site in southern Anatolia | Murat Özsoy 1958 / WIkimedia Commons

Planting history may be rewritten

Of course, wheat also has its place in China. So far, wheat has been unearthed in more than 30 different archaeological sites in a belt of thousands of kilometers from the eastern edge of the Tianshan Mountains in the west to the Shandong Peninsula in the east. These samples belong to the Longshan period about 3,000 to 4,000 years ago. The current academic theory is that after wheat originated in West Asia, it was introduced into China through the Eurasian grassland channel about 5,000 years ago and spread to various prehistoric civilizations in North China. The genome analysis of these ancient wheats also proves that they are indeed related to modern Chinese wheat.

Main distribution area of ​​Longshan culture | Kanguole / Wikimedia Commons

However, there is still a long way to go from eating wheat to large-scale cultivation. There was an early theory that wheat was not cultivated on a large scale until the Han Dynasty in China. For example, among the crop seeds floated out from the Erlitou site of the Xia Dynasty, millet and rice accounted for more than 90%, and there were also a small amount of yellow rice and soybeans, while only a dozen grains of wheat were found. Although there are records of "告麦" in the oracle bones discovered in the Shang Dynasty, the proportion of wheat unearthed is still not high.

Millet (left) and rice (right), still common grains today | Left: STRONGlk7 / Wikimedia Commons; Right: Augustus Binu / Wikimedia Commons

Therefore, the discovery of a large number of wheat seeds at the Haojing site of the Zhou Dynasty in Xi'an can be regarded as a historic breakthrough. In fact, after analyzing the proportion of wheat seeds in archaeological sites of different periods, researchers found that the Western Zhou Dynasty was the key period for the intensive use and popularization of wheat. After that, records about wheat can be seen in historical books.

So, do you want to eat some wheat today? Bread? Steamed buns? Pancakes? Or a bowl of Chongqing noodles~

References

[1]https://en.wikipedia.org/wiki/Paleobotany

[2] http://www.kaogu.cn/html/cn/xueshuyanjiu/yanjiuxinlun/kejikaogu/2013/1025/33575.html

[3] http://www.kaogu.cn/cn/xueshuyanjiu/yanjiuxinlun/kejikaogu/2015/1106/51923.html

[4]https://new.qq.com/omn/20191015/20191015A0IIR600.html?pc

[5] http://www.kaogu.cn/cn/xueshuyanjiu/yanjiuxinlun/xinfangfa_xinsilu/2018/0226/61181.html

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