Catastrophic floods, devastating droughts, rising sea levels, and more – throughout history, countless societies have felt the impact of significant changes to the environments in which they live. Several new studies are revealing how past climatic events influenced different cultures around the world, exploring how they were affected and the ways in which they adapted to these new circumstances, to varying degrees of success.
Collapse of the Liangzhu
The Liangzhu culture in eastern China, which thrived in the Yangtze Delta from c.5,300 to 4,300 years ago, was one of the world’s most advanced Neolithic cultures. At its heart was Liangzhu ancient city, a vast walled settlement covering c.290ha. It featured a large palace complex, a sophisticated jade industry, and a complex water-management system that operated both within and outside the city walls, consisting of canals, dams, and reservoirs that made it possible to cultivate large agricultural areas throughout the year (below).
But c.4,300 years ago, the ancient city was suddenly abandoned and the Liangzhu culture collapsed. The reason for this abrupt decline has remained the subject of debate since the city’s discovery in 1936. Suggestions have included war and internal social conflicts, rising sea levels, and harsh climatic conditions such as a period of extremely cold temperatures, but by far the most popular explanation has always been flooding. A layer of silt found overlying the late Liangzhu cultural layer in many excavations was thought to have been deposited during a huge flooding event, and this hypothesis has now gained further support thanks to a new study investigating palaeoclimatic data from the region.
In a paper recently published in Science Advances, researchers present their analysis of samples from stalagmites in Shennong and Jiulong caves, several hundred kilometres south-west of Liangzhu ancient city (below). The isotopic records of these cave deposits act as an archive of the climate in the lower reaches of the Yangtze River Valley as far back as 14,000 years ago. Data from the stalagmites, combined with other palaeoclimatic and archaeological evidence from the region, provide clear signs of extremely high precipitation around the time that the Liangzhu culture collapsed. It is thought that unusually intense monsoon rains c.4,300 years ago and unprecedentedly wet conditions in the decades that followed could have led to huge floods that had the potential to destroy the Liangzhu’s hydraulic management systems and their rice cultivation, making it impossible to live and farm in the low-lying land. This forced the Liangzhu people to abandon their capital city and settlements in the Taihu Plain, ultimately leading to the downfall of their civilisation.
Brazil’s coastal communities
In Brazil, new research is showing that decreasing water levels could also have a significant impact on past societies. The presence of pre-Columbian communities living along the southern coast of Brazil, exploiting coastal resources during the Middle and Late Holocene, is known to date back at least 7,000 years. These fisher-gatherer communities left behind shell mounds known as sambaquis (below), which offer the main form of evidence for their presence in the region. However, c.2,200 years ago the frequency of these sambaqui sites declined dramatically. This shift in the archaeological record coincides with a significant change to the coastal environments in which these communities lived, with falling sea levels, increased rainfall and an intensification of cold weather that disrupted aquatic life in areas like estuaries and lagoons.
Now researchers have shed new light on the human response to these environmental changes. The study, recently published in Scientific Reports, looked at almost 300 human remains and over 400 radiocarbon dates from archaeological sites along the coast of south-eastern Brazil. Through analysis of stable carbon and nitrogen isotopes, they identified several significant changes in the diets and subsistence strategies of these coastal communities c.2,200 years ago.
Perhaps surprisingly, it appears that they did not switch their focus from coastal resources to different food sources, but instead increased their reliance on fishing. In particular, there was a marked increase in their exploitation of species at the top of food chains, including sharks and rays, in contrast to their earlier dependence on species that came rather lower in the pecking order, such as molluscs.
The environmental shift also seems to have coincided with an important social change. Before c.2,200 years ago, the majority of these societies practised community-based sharing, with resources such as food distributed among a wider group. However, as shrinking coastal ecosystems led to less predictable and abundant aquatic resources, these people split into smaller social units, with resource-sharing decreasing to a more restricted level. The settlements of these smaller groups are far less visible in the archaeological record, which goes some way to explaining the decline in the number of sambaqui sites found along the Atlantic Forest coast in Brazil after this point.
Maya drought resistance
In the Yucatán Peninsula, another story of adaptation to climatic changes is being uncovered. Around the end of the 9th century AD, a series of droughts are known to have occurred across south-eastern Mexico and northern Central America, at a time when population numbers began dropping at many Maya cities. It has previously been assumed that these droughts led to a famine that devastated the Maya, who were believed to be largely reliant on several plant species that were very sensitive to drought, including maize, beans, and squash (below).
However, new research published in the journal PNAS has revealed that the Maya had access to almost 500 types of edible plants, many of which are highly resistant to drought. Using a master-list recently put together by one of the study’s authors, Scott Fedick, the researchers have analysed the drought resistance of all 497 indigenous food plant species known to have been used by the lowland Maya, in order to determine which foods would have been available during different levels of drought.
They found that even a less severe drought would have had an impact on food availability – with the number of food-producing species reduced to 413 under a short-term drought, and 108 under a moderate drought. It would have particularly affected species that were commonly eaten by the Maya, such as squash and beans, and would therefore have necessitated shifts in dietary patterns. It seems, however, that there would still have been many food plants available in all but the most extreme circumstances. During a severe, multi-year drought – and there is no clear evidence that this point was ever reached – the Maya in the Yucatán Peninsula would still have had access to 56 species of edible plants that were highly drought resistant, including edible roots (among them manioc, papaya, and yucca), edible plant stems (such as heart of palm and cactus pads), and bark from several species of trees.
It remains uncertain why Classic Maya society declined c.1,100 years ago, and it is very possible that the droughts were a contributing factor, potentially causing famine, migration, and social decline, but this new research confirms that the overly simplistic explanation of droughts leading to complete agricultural collapse and therefore the downfall of society is insufficient.
FURTHER READING H Zhang et al (2021) ‘Collapse of the Liangzhu and other Neolithic cultures in the lower Yangtze region in response to climate change’, Science Advances (www.science.org/doi/10.1126/ sciadv.abi9275). A Toso et al (2021) ‘Fishing intensification as response to Late Holocene socio-ecological instability in south-eastern South America’, Scientific Reports (https://doi.org/10.1038/s41598-021-02888-7). S L Fedick and L S Santiago (2022) ‘Large variation in availability of Maya food plant sources during ancient droughts’, Proceedings of the National Academy of Sciences (https://doi.org/10.1073/pnas.2115657118).
