[Originally posted Jan. 20, 2011]
I recently came across this news item on Science AAAS. I have no doubt that it is an interesting and important study of tree rings and the conclusions can help us understand many things in human and environmental history. However, some of the suggestions drawn from the results are rather far fetched, to say the least, and are in fact typical of an ailment common to many natural scientist that turn their attention to the evolution of human societies, an ailment called environmental determinism (it occasionally affects historians and archaeologist as well). This is the general attitude or tendency to seek environmental causes for most important developments in human history. Usually it is supposed to have something to do with climate (understandable given the modern preoccupation with global warming).
Fortunately, not all natural scientists that take an interest in human society suffer from this affliction and the names of D.S Wilson and P. Turchin come readily to mind. Both of them have studied human society in a most sensible manner, not as something that is simply subject to the vagaries of the natural world but rather as something that is actually a part of the natural world and subject to the same general principles. By studying human societies in this way we will actually discover that our societies are not just a normal part of nature but rather an interesting and new development in the evolution of life on earth. And this new development is actually something that profoundly contradicts the basic premise of environmental determinism.
The problem with environmental determinism is that it underestimates human society in two different but connected ways. On the one hand it underestimates the complexity of human society and history and on the other it underestimates the adaptability of human societies.
Human societies are the most complex phenomena known to us. This should warn against adopting simplistic explanations for historical processes that are intrinsically complex. Human societies evolve on their own terms and they do not necessarily react in a simplistic or even predictable way to environmental stimuli. This is not to say that environmental fluctuations do not matter but rather that how societies react to them is not always straight forward.
Furthermore, because of the extreme variety and complexity of human societies there is always a lot of things going on. If we compare some environmental variable (like climate) to what we know of history we can always find something that seems to match. Take for example the ‘Little Ice Age’. It is often asserted, in a environmental deterministic fashion, that this cold period that lasted approximately 1600-1900 AD (actual estimates vary) was a primary cause of the ‘decline’ of Icelandic society (which in turn is highly problematic – but let’s not get into that). The period of ‘decline’ is approximately the same as the Little Ice Age so it all seems to fit. However, a simple correlation does not necessarily indicate a causal link. When we are dealing with a very complex and variable reality, correlations often appear at random and the environmental determinist should consider that the Little Ice Age was not confined to Iceland. It was a cold period all over the world, not least in Europe which, at that time, developed the modern state, industrialization, unprecedented population growth, democracy and modern medicine. Did these things have anything to do with the Little Ice Age. Probably not much and at least not in any predictable, simplistic way.
Another example can be taken directly from the news item mentioned at the beginning where is says: „Around 1300 C.E. […] a cold snap combined with wetter summers coincides with widespread famines and plague that wiped out nearly half of Europe’s population by 1347.“ Actually the plague only started in 1347 and certainly didn’t manage to kill nearly half of Europe’s population until several years later. But never mind that. It is suggested that the plague was somehow the result of climate change and this is apparently based on nothing but the rather incidental correlation in time. How are we to assume that the colder and wetter climate caused plague bacteria to travel from Central Asia (where they were endemic) to Europe? Where they just tired of the dry continental climate and longed for some rain?!
This was not the first time the plague bacterium appeared in Europe. The Plague of Justinian that started in Constantinople in 541 AD was probably the same disease (the bubonic plague) and was most likely just as devastating. Just like the 14th century plague, it reoccurred over a period of about 150 years, severely reducing population and recovery didn’t star in earnest until around 700 AD. Was this plague also the result of a colder and wetter climate? The news item doesn’t say. I am quite sure that we could find some kind of climatic variation around 541 if we look hard enough but I seriously doubt that it had much to do with the Plague of Justinian.
The second and even more serious problem with environmental determinism is that it underestimates the adaptability of human societies. This adaptability is actually closely linked to the complexity of human societies and it has made them the most adaptable phenomena that we know of and by a very large margin. The basic reason for this adaptability is that the emergence of culture has largely replaced genes as the blueprint for behaviour in our societies. Culture and genes are in many ways similar, they both determine behaviour, however culture evolves at a much faster rate than genes do and, consequently, cultural evolution and cultural adaptation works on an entirely different timescale from genetic evolution. In this, humans are a unique species on this earth. Other animals may have evolved some tiny spores of culture but only humans have turned it into its major survival tool and had it replace genes as the basic adaptive mechanism. This is why humans are not as vulnerable to environmental changes as other animals are. Through their culture, they can actually adapt in real time as the changes are happening, usually without major catastrophes. What constitutes a major catastrophe is of course relative and famines are familiar occurrences in human history but most of them are mere peanuts compared to what other species have to endure.
Not all human societies are equally adaptable and generally speaking they have become more so as they have grown more complex. The most complex societies have actually done away with famines for good. The invention of farming (first about 10-12 thousand years ago) was a major step in increasing human adaptability. With a variety of farming methods to choose from, a slight shift in climate (as have often occurred) was not an insurmountable problem. One could replace wheat with barley, turn some cornfields into hayfields or shift emphasis from cattle to sheep all as the circumstances called for. Therefore, people were usually not just some helpless victims when faced with environmental changes. They could adjust their survival strategy and survive with relative ease.
Of course I do not mean to suggest that human societies are immune to environmental changes. Far from it. But the human-environmental relationship is far more complex and dynamic than environmental determinists imagine. Human societies have occasionally suffered from catastrophic environmental changes and been devastated by them. But most changes are relatively minor and human societies have been able to handle them without much difficulty. They do not one-sidedly determine human history, rather they are stimuli that can often affect societies in subtle and unpredictable ways but only rarely do they directly cause major upheavals.