The authors of The Climate Connection: Climate Change and Modern Human Evolution are deeply aware of the threat to human survival accompanying our rising greenhouse gas emissions. Renée Hetherington and Robert G.B. Reid suggest that a better understanding of our past evolutionary relationship with climate may point to how we may yet make the future more hopeful than it presently seems. Not because the climates homo sapiens has had to live with in the past resemble what we are laying up for our future, but because the authors see elements in past human responses from which we might learn if we will.
The book covers a wide field, dealing with the emergence of modern humans, the dispersions and migrations of human populations, the climate changes of the last 350,000 years and the interaction between climate and humans during that time, concluding with reflections on our future in a very different climate environment. The survey is designed for those with courses of study in view or already working in the area and is hence often demanding for the general reader. It contains much detailed and carefully referenced information in its pages. However its underlying themes are regularly stated and provide ample bearings for readers for whom the territory is not familiar.
In discussing human behavioural evolution the authors espouse the working hypothesis that from the outset homo sapiens has had the potential to express the same thoughts, ideas, communication, spirituality, artistry and technical complexities as our own brains. But a combination of environmental conditions, both favourable and stressful, and increased social complexity was needed to bring out that potential. Robert Reid, a biologist, is a proponent of emergent evolution and a critic of the adequacy of natural selection theory. The book argues that environmental and climate connections have elucidated rapid changes in human behaviour in the past. Adaptability is required under conditions of stress and climatic instability which demand disregard of old ways and the adoption of new. Such adaptability has been demonstrated in human populations.
The book makes a long and careful journey looking for times when rapid behaviour change might have occurred. The “out of Africa” hypothesis underlies the authors’ survey, with much attention paid to early human mobility and migration. Geographical barriers to human movement, expansive coastal plains exposed when sea level fell during glacial periods, possible congregation of populations in productive refugia in glacial periods leading to increased genetic exchange, are among the factors the book considers as it surveys the evidence of the dispersal of behaviourally modern humans in the various regions of the world. The authors give especially close attention to the Americas where they have a greater research background.
A substantial section of the book examines climate during the last glacial cycle in considerable detail. It includes an excellent description of climate change forcing mechanisms. The authors have recently used the UVic Earth system climate model, which they describe as of intermediate complexity, in a project to understand the world’s changing climate over the last 135,000 years. Combining modelling with proxy indicators they try to reach a best estimate of the climate and its effects on vegetation over a number of different stages during that time. This is the changing world that our ancestors moved through and inhabited.
What did the changes mean for those ancestors? The book frankly acknowledges the huge gaps in any picture we can hazard constructing. The words ‘may’ and ‘likely’ occur frequently. But it painstakingly matches any fossil and archeological evidence that can be matched and emerges with some general observations which certainly seem worthy of consideration. One in particular sounds a theme recurrent in the book. In the course of the glacial cycle they see probable migration out of deteriorating regions and into more habitable areas where disparate groups would be periodically placed in social contact with one another. It is this sort of social interaction that they consider likely to have stimulated the emergence of intelligence and the development of new ideas and technologies. Eventually the relatively more settled climate of the Holocene led to the development of agriculture which allowed humans to directly manipulate the unpredictability of nature, albeit sometimes precariously as the chapter surveying the history of agriculture makes clear.
Is all this any help as we face a climate changing because we are causing it to change, with prospect of an altered kind of world from that in which human civilisation developed? We’re in a different situation from our roving ancestors. The authors point out that there are 6.75 billion of us now, expected to rise to over 9 billion by 2050. The global dominance we have achieved as a species has been achieved as we have discovered how to manipulate our environment. But with environmental manipulation has come the unintended consequence of human-caused climate change bringing the threat of severe economic and social instability. On a planet so heavily populated and whose resources are so stretched it is not possible to replicate a past when humans could migrate to new regions relatively unobstructed.
What then can we learn from the past experiences of our species? It has to be said that the authors are hardly confident as they address the question towards the end of the book. However they do their best. In our past real changes in behaviour occurred when humans experienced significant environmental stress. They note that major environmental stress is clearly predicted in our future, so behavioural change may potentially be on the way. But they recognise that the problem is that we must change now before climate change puts us under those stresses. In effect, then, they suggest anticipating the stresses and opting for changes before they are forced upon us. Even as they do so they recognise that it’s by no means clear that we can manage this. For example they rather chillingly refer to Jared Diamond’s Collapse which speaks of ‘creeping normalcy’ as a major reason why people fail to recognise a problem until it is too late. Further, they note that Diamond states that even when the problem is recognised societies frequently fail to solve it because people are highly motivated to reap big, certain and immediate profits, while the losses are spread over large numbers of individuals.
Nevertheless in spite of all the negative possibilities the authors emphasise that the important message from past human interactions with climate is that we should work co-operatively in finding innovative solutions which will lead to the global sustainability which we have placed under threat. Revolutionary ideas have been stimulated in the past in response to rapidly changing environmental conditions and as a consequence of concentrating populations. Reluctance to change leaves us highly vulnerable to decline, and even extinction.
This advice is hardly new. It comes at us from many directions. But for the authors of this book it is reinforced by all they know of the long story of our species. The intrinsic interest in what they have to tell of that story is enhanced by their ever present sense of how it might assist us in understanding and confronting the challenges ahead for our species.