New Grain Theory

BANDANA SAMANT LOOKED through a powerful microscope at a sample of ancient dinosaur faeces to find something remarkable. This was a few years ago. Samant, a bespectacled professor at Nagpur University, was part of a team of international researchers that was exploring the excreta of dinosaurs, excavated a few kilometres away from a tiny village in Maharashtra, to put together the dietary habits of these giant reptiles. There in the dung, from a species identified as Titanosaurus, considered to be among the largest dinosaurs, visible through the microscope, was evidence of digested rice.

For several years, Pisdura, the tiny village a few kilometres from Nagpur, has thrown up a vast number of dinosaur fossils, eggs and bones. But what has been most striking here is the surfeit of coprolites or dinosaur excreta among them. It has been theorised that lava from volcanoes in this part of India flowed over dinosaur bodies, bones and their excreta for thousands of years, fossilised them, and has now turned this village into such an important palaeontology site.

Analysing the dung from Pisdura, researchers had already established that dinosaurs were picky eaters: the dung contained far less plant residue than the fossilised plant residues in nearby sediments, and closer examination revealed that the beasts, at least in these parts, preferred soft plant tissue instead of the hard and woody. Also, that they consumed grass, which was interesting because grass has long been considered a relatively young evolutionary group but this discovery pushes its origin back to at least 65 million years ago. And now, Samant and her team had discovered that dinosaurs also ate wild rice. “All this is very controversial. Most people believed wild rice probably emerged 25 million years ago in eastern Asia. But we had found something very, very different,” she says. “Nobody had looked at whether grass or rice was consumed by dinosaurs. Because grass is believed to have emerged long after dinosaurs vanished.”

Here, however, was wild rice as microscopic silica bodies in a 65-million-year-old remnant of dinosaur excreta, proof not just that wild rice was around back then, but also part of the diet of fussy dinosaurs. Note that 65 million years ago, India was not a part of Asia. It was a large island still south of the equator, having just broken off from modern-day Madagascar and moving northward to eventually collide into the landmass that we now know as Asia. Could it be that wild rice did not originate in eastern Asia, as previously believed, but that it was already growing on the drifting land mass now called the Indian Subcontinent, and that after its collision into the Asian land mass, rice and other types of grasses dispersed from here to the rest of the continent? For palaeobotanists and scientists trying to trace the origins of rice, such a possibility is the equivalent of a wet dream.

The origin of rice, both as a wild plant and domesticated crop, is hidden in a fog of obscurity. We do not know with certainty when it first emerged as a wild plant, and, more crucially, when and where exactly it was first planted and grown by humans. The crop has been scrutinised by archaeologists, researchers and genetic scientists for years, all of who have offered a wide variety of claims and counter-claims, but no theory has yet come close to offering absolute clarity.

The interest is understandable. Rice is arguably one of the most important crops in human evolutionary history. This single variety of grain transformed hunter-gatherers into agricultural farmers in Asia. It led to the earliest urban centres; it transformed landscapes. Wherever might be the location of its first domestication, the crop spread across the world. It travelled to Persia, Mesopotamia and Turkestan. It travelled with Arab caravans to Egypt, Morocco, Spain and the rest of Europe, and from there, onboard ships to European colonies in Africa. And from Africa, it is believed, it made its way to America. When Alexander the Great invaded India in the fourth century BCE, some say, one of the prized possessions he carried back with him was rice.

Finding the birthplace of this crop isn’t just an academic pursuit. It is also a matter of pride. As Jennifer Bates, an archaeobotanist specialising in South Asian archaeology, and Cameron Petrie, a researcher specialising on the archaeology of India, Pakistan and Iran, both from the Department of Archaeology in Cambridge, say, where and when rice was first domesticated ‘is a huge question, and difficult to answer simply’. ‘Questions surrounding whether modern rice stemmed from a single origin… to multiple origins… have relied heavily on genetic evidence,’ they say over email. ‘However, due to the hybridizing nature of rice and its subsequent genetic complexities, this picture remains difficult to resolve…’

The general consensus currently points to a place somewhere either in modern-day China or India between 8,200-13,500 years ago where rice or Oryza sativa was first domesticated from wild grass. There is another cultivated species, Oryza glaberrima, but that was grown much later in West Africa. Some have posited other places as the birthplace of rice, like one study that claimed to have found evidence of 15,000-year-old burnt rice grains in South Korea, but these have been viewed with scepticism.

Between India and China, the latter has been the favourite, with several researchers contending that rice agriculture began in the lower stretches of the Yangtze River Valley in the country’s east. Some have suggested the Pearl River Valley in southern China could be another site. Others have argued that Oryza sativa, and both its two main subspecies, japonica, the short-grained rice prevalent in the subtropical and temperate regions of East Asia, and indica, the long-grained variety common in tropical regions like India, came from a single domestication event that occurred between 8,200 and 13,500 years ago along the Yangtze river. Others have argued that it happened multiple times and independent of each other both in China and India. A few point the other way around, arguing that rice was first grown in India, before it made its way to China.

Genetic studies have so far not been able to settle the debate. Some studies on the subspecies indica and japonica have found that the two are more closely related to distinct wild varieties than they are to each other, pointing to two separate domestication events, the japonica in China and the indica in India. Other genetic studies have pointed to a shared history. In 2006, an article in Nature mentions a study identified a gene variation, sh4, in both japonica and indica subspecies of domesticated rice that prevents rice grains from shattering. Other papers have found similar such gene mutations, and these have often been found to have arisen in an ancestor of japonica rice first before showing up in indica. Have all modern rice subspecies thus emerged from a single domestication event? Or, were there many such events with no link to each other?

The journal Current Science recently published a study conducted by three researchers from Lucknow’s Birbal Sahni Institute of Palaeosciences that finds far older dates of rice cultivation than any discovered in China. According to the study, rice was being cultivated in India as far back as 9,250 years ago. The evidence was found in the form of diatoms—unicellular micro-organisms that usually occur in water-bodies and which when present in a paddy field, for instance, carry a unique signature of that history. The diatoms were discovered close to an archaeological site that in the past has thrown up, according to the researchers who found it, evidence of charred rice grains close to 8,500 years old.

The current evidence, 9,250-year-old diatoms, however, was found at the bed of a lake. The archaeological site close to it is Lahuradewa in the Sant Kabir Nagar district of Uttar Pradesh. But how do diatoms get deposited in lake-bed sediments? According to Biswajeet Thakur, who along with Anju Saxena and Inderbir Singh made the discovery, the shores of the lake were probably used to grow crops. During the monsoons, they argue, the water body would probably expand and paddy would be transplanted to marshy patches. After the end of the monsoon, once those margins dried, the crop would be harvested. “But when there would be floods (during the monsoons), sediments along with microcharcoal, rice phytolith and paddy field diatoms would be transported into the deeper part of the lake,” he says.

AS THAKUR EXPLAINS, diatoms are usually of four major types: those that occur in paddy fields (paddy field diatoms), those caused by high pollution (anthropogenic diatoms), those that form in free-floating water bodies, like lakes (planktic), and those that live on sediment surfaces (benthic diatoms). Thakur and his colleagues dug a 2.8-metre deep trench in the eastern part of the lake, collecting samples from different depths for radiocarbon dating, each progressive depth signifying an earlier time period. At the depth that was equivalent to about 9,250 years earlier, Thakur says, a large number of paddy field diatoms started showing up. “There was also human activity near the lake leading to an organic pollution of lake water during this period. Because we also begin to notice anthropogenic diatoms (caused by pollution) flourishing and increasing,” he says, indicating that cultivation might have been occurring leading to the pollution.

Thakur has been working on diatoms for the last 12 years. He is interested in using diatoms to study the period around 11,000 years ago in India, he says, when early farming practices probably started being adopted around fertile river banks, like the Ganga’s. “We know very little about this period. Were there settlements in India as early as others? Were there migrants who settled into these parts?” he asks. “We are beginning to find all sorts of things around this time in these parts—evidence of things like anthropogenic activity in the form of micro-charcoals, evidence of (agricultural) activities like slash-burning (where forest land is cleared and vegetation burned to provide land for agriculture) about 15,000 years old in the Gangetic plains.”

According to Thakur, there is now sufficient proof to believe that rice domestication took place in India independently, and, as his study suggests, before its cultivation elsewhere. “We have the oldest dates. I think there is a big chance that it was first domesticated here,” he says.

Thakur points to the 2008 study where nearly 8,500-year-old charred rice grains from Lahuradewa were found to buttress his study’s findings. Then, the grains were claimed to have been of a domesticated variety. Other researchers are not fully convinced, pointing out that the grain length, width and thickness ratios of these grains significantly overlap with those of wild grains, and that the findings probably point to the beginnings of a long history of wild rice cultivation.

Some researchers are sceptical about Thakur’s latest findings. ‘This paper talks about evidence for paddy at Lahuradewa, but it is not clear what they have found. The argument hinges on the microfossil data (diatoms and phytoliths) from cores taken at the edge of a lake, but it is not clear that it is possible to establish paddy from diatoms alone in lake contexts, or whether the phytoliths are from domesticated rice,’ Bates and Petrie say. ‘This paper does, however, represent a fascinating addition to the prehistory of rice in South Asia.’

Thus if the latest findings from the lake and even the nearly 8,500-year-old charred rice grains discovered at Lahuradewa point not towards domesticated rice but simply to the exploitation of wild rice, the only conclusive evidence we have so far of the earliest dates of cultivated rice in India is from the Gangetic region of Mahagara in UP, where proof of such rice crops dating back to 1800 BCE have been found.

What then of the intervening period, which happens to be that of the Indus Valley Civilisation? Were their meals as sophisticated as the rest of their civilisation? Did rice, which had surely been domesticated by then—in China if not India—figure in their diet?

Over the years, there has been significant evidence which indicates that rice was consumed by Harappans. Impressions of rice grains have been observed, for instance, in pottery at sites in Gujarat and Rajasthan and actual rice grains have also been recovered from some sites. But these have not been securely dated, and the chronology presented in the reports, as researchers point out, is opaque.

Thus a consensus seems to have developed which argues that either rice was available as a crop in the Indus Valley region but it was unimportant and not adopted, and its importance rose probably only towards the Late Harappan period in 1900 BCE (this is also around the speculated time when japonica is said to have arrived from China), or that the role of rice changed from a secondary crop in the late Mature Harappan (2600-1900 BCE) to become a staple either in the Late Harappan periods (1900-1300 BCE), or the period immediately after.

But Bates and Petrie, who have been studying the role of rice in the Indus Valley period, have found something else entirely. According to them, far from being a scarce resource, rice was present in Early, Mature and Late Harappan phases and in large proportions relative to other popular cereals. They argue that rice was one of the staple crops and part of a complex multi-cropping strategy. The two found evidence for a different domestication process here, likely based on the wild species Oryza nivara leading to the local development of a mix of ‘wetland’ and ‘dryland’ agriculture.

BATES AND PETRIE point to a 2017 study conducted by JY Choi on the genetics of indica, aus and japonica subspecies that argued for a single domestication event but with gene flow into multiple other populations of wild rice species, resulting in what they term a multiple origin, single domestication model. ‘Their model states that domestication in its full sense only occurred in japonica rice, from wild rufipogon, starting in China… and this resulted in later introgressive hybridisation with populations of what they term ‘proto-indica’ and ‘proto-aus’. (Introgressive hybridisation is the movement of a gene from one species into gene flow of another by repeated backcrossing of an inter-specific hybrid with one of its parent species.) These ‘proto’ species resulted from wild populations of other rice species such as nivara in India. The hybridisation led to gene flow in domestication alleles into proto-indica… and proto-aus… and to full domestication of these rice species,’ the two say. ‘(Dorian) Fuller (an archaeobotanist)… has similarly argued that the ‘independent rice tradition in north India… never… proceeded on its own to full domestication’…. These findings demonstrate the ongoing process of domestication, rather than the final stages of domestication, suggesting that the proto- indica hypothesis, demonstrating that rice was undergoing a local domestication process… and was at least semi-domesticated before japonica arrived… and hybridised with the local proto-indica to make rice as we know it today.’

What makes matters interesting is the possibility that much of early rice cultivation in South Asia centred around the wild Oryza nivara. This species is different from the Chinese wild rice, rufipogon. While rufipogon is a grass that grows only in permanently wet soil, often far from shore, and produces less seed in unpredictable yields from year to year, nivara is an annual grass of seasonally monsoon-inundated ponds, which produces high yields with little need for interference or manipulation of the environment or plant. It could thus be effectively exploited in its wild state, discouraging intensive cultivation and the selective pressures that would eventually lead to domestication.

According to Petrie and Bates, one of the problems in the discussion on rice domestication is that wild rice is often inextricably linked with simple cultivation, while domesticated rice is linked with more complex forms of agriculture. Whereas in reality, they say, the Indus populations may have been exploiting semi-domesticated or even domesticated nivara or indica subspecies in a managed agricultural system.

‘[All the] data… suggests that when… japonica was introduced around 2000 BCE,’ according to Petrie and Bates, ‘It arrived in an area that was already familiar with domesticated rice cultivation and a range of cultivation techniques.’

The Rice Line: A brief history of growing paddy

• A study finds wild rice in dinosaur excreta, at least 65 million years old, in India, evidence that dinosaurs consumed them. Wild rice, and even grass, have never been considered to be this old. 65 million years ago, India was an island that had broken off from Madagascar and was yet to collide with Asia. Could wild rice have originated in India, and after its collision, spread into Asia?
   
• Another study finds evidence of domestic rice cultivation 9,250 years ago in a small village in India. An older study close to the area found charred rice grains estimated to be over 8,000 years old. Others argue both studies have probably found evidence of wild rice, not domesticated rice
   
• It is widely believed that rice, or Oryza sativa, was first domesticated by humans from wild grass in a single event along the Yangtze River Valley in eastern China at least 8,000 years ago. Others argue rice cultivation began multiple times, independently of each other, both in China and India. A few believe rice was first grown in India before it made its way to China as an agricultural crop
   
• Another domesticated rice variety was developed in Africa, Oryza glaberrima, probably along Niger River in West Africa, a few thousand years after Asian farmers
   
• Rice seems to have been a staple crop in Indus Valley across its various phases. The domestication process here was probably of the wild species Oryza nivara. When japonica arrived from China around 2000 BCE, this area in India was already familiar with domesticated rice cultivation
   
• Genetic studies have found similar gene mutations in both major subspecies of Oryza sativa, with the mutation first occurring in an ancestor of japonica, commonly found in China, before appearing in indica, found in India, suggesting a single domestication event in China

agricultureChinaIndiaoriginricescienceSouth East Asia