Human Behavioural Plasticity
Updated: May 21, 2021
How is it that our species has come to inhabit almost every corner of the globe?
Hunter gatherer mosaic reduced. (Source: Rawpixel Ltd, Creative Commons.)
How is it that our species — Homo sapiens — has come to inhabit almost every corner of the globe, from high mountain peaks to freezing tundra, arid deserts to coral atolls and impenetrable rainforests? The deep history of this phenomenon can inform us about where we might be heading in the coming centuries.
Our species is ‘behaviourally plastic.’ That means we have the ability to settle in novel, unpredictable, and harsh environments by transforming the world around us, and by modifying our own behaviours to mitigate ecological challenges. This creative capacity to reshape our social and physical surroundings accounts for much of the diverse cultural behaviours that make us Homo sapiens, whether it is art, music, language, architecture, or trade.
Behavioural plasticity emerged relatively recently over the last few hundred thousand years during the Ice Ages. Archaeologists call this the Pleistocene period — a time of compressed temperatures and climatic instability, during which the Earth would regularly switch between cold, dry glacial conditions to warmer, wetter settings in the space of only a few decades or centuries. These switches prompted glaciation, forest expansions and contractions, animal extinctions, and sea level changes.
In this period, Homo sapiens expanded out of Africa and into a wide array of ecological zones including the frozen tracts of northern Eurasia, the small islands of the western Pacific, and the tropical rainforests of Southeast Asia. These early explorers were foragers, hunters, and fishers and they lived in small but dynamic communities that frequently moved around the landscape. It was these explorations of new environments that encouraged the increasing expression of behavioural plasticity and allowed humans to adaptively respond to periods of rapid climatic change.
A future in which Homo sapiens persist as low-density populations of mobile foragers would not mean the end of the human story, but rather a new trajectory.
If the instability of the Pleistocene period sounds familiar, it is because we are expecting the 21st century to be characterised by similar kinds of climatic flux. The human capacity to remake the world around us has pushed the planet to a dangerous new precipice, and populations in industrialised nations have set in motion a process of global heating that will likely see average temperatures rise by 3–5° C in the next century, and perhaps 8° C or more during the next millennium. Alongside this, we are already beginning to observe the resulting deglaciation, rising sea levels, and more intense storm and drought conditions.
Although our ancestors responded dynamically to environmental change in the Pleistocene, most people today live in sedentary, agrarian, and urban settlements — highly complex social settings that have arisen within the last 10,000 years, but are in many ways poorly suited to respond to major environmental changes. People living in these communities tend to assume that this social, political, and technological complexity will allow us to outthink global heating, keeping one step ahead of the temperature curve. But we are also increasingly becoming attuned to the ways that this complexity can hinder unified and meaningful responses to the problem.
What might the future for Homo sapiens be if we aren’t able to collectively modify our behaviours in time? As people, particularly in low-income rural communities, become more mobile due to failed crop yields, droughts, flooding, sea level rise, and food shortages, perhaps the future of human behavioural plasticity lies not in urban settlements, but in less cumulatively ‘complex’ and therefore more adaptively flexible societies that are more responsive to local change. Social scientists are beginning to think seriously about this prospect, and whether urbanism, monoculture, and surplus resource extraction will simply be a very short experiment in a timeline otherwise marked by foraging, egalitarianism, and high mobility. It is quite possible that the next hundred thousand years of human history will be one of hunting and gathering, and more similar to the Pleistocene than we might think.
By examining the deeply interwoven history of human adaptation and climatic change it shows us that our species does have the capacity to transform our behaviours in response to monumental and often existential environmental risks. Whether industrialised societies can do so in their present form remains to be seen. But a future in which Homo sapiens persist as low-density populations of mobile foragers would not mean the end of the human story, but rather a new trajectory.
Dylan Gaffney  is a New Zealand trained archaeologist. His current research examines how humans came to inhabit and adapt to island rainforests for the first time.