Over the second half of the 20th century, there were spectacular gains in life expectancy in many parts of the world. Now we are living longer, why is there a widespread perception that we are feeling worse? This is the central paradox regarding health at the beginning of the 21st century, and the ultimate target of much of the detailed historical, environmental and biological material in this important book.
There is, of course, more to health than a long life. Psychological ill-health is becoming increasingly apparent, perhaps in response to urbanisation leading, in Thoreau's words, to millions of people being lonely together. Old age is not a blessing if you are sad, sick or struggling to get by.
The worldwide rise in cases of obesity, diabetes and asthma indicate that "progress" can have its drawbacks. Health improvements across the 20th century have also been experienced unevenly, with the poor in rich countries and most of the population in poor countries having gained much less than the affluent. The optimism of two or three decades ago about the eradication of infectious diseases, has been reversed. When the US surgeon-general declared in 1970 that it was time "to close the book on infectious disease", stories about the advent of HIV-Aids, the spread of hepatitis C, the advent of antibiotic-resistant bacterial strains and the re-emergence of TB would have been regarded as scaremongering.
Furthermore, the economic and technological growth that has underlain the improvements in health for most of the affluent world has been bought at the cost of non-sustainable environmental degradation. If all 6 billion inhabitants of the world were to share the consumption patterns of the affluent West, we would require two extra planet earths to cope.
At the beginning of the 21st century, we probably experience both unprecedentedly good health and anxiety about what the future holds. To get a sense of what level of anxiety about the future is appropriate, Tony McMichael goes back to the origins of human societies - and before. The journey is fascinating. The shift of our ancestors from an exclusively vegetarian diet to one containing meat 2 million years ago was accompanied by a relatively greater investment in brain power rather than jaw size. The exclusively vegetarian line became a dead-end, masticating its way to extinction. The origins of agriculture 15,000 years ago created an advantage for those who could tolerate a diet with a high carbohydrate load.
Being what is now called "insulin resistant", and thus prone to diabetes, could have been the original state, from which European farming populations represent a deviation. Similarly, being intolerant to dairy products appears to be a genetically faithful inheritance from our ancestors, disrupted 8,000 years ago by the domestication of goats, sheep and then cattle. The notion that there are aberrant "genes for diseases" waiting to be discovered is simplistic. The history of human health is not just a story of progress. The shift from hunter-gathering to agriculture enabled the support of larger and more concentrated populations, but with the cost of a more precarious existence, with crop failure a constant possibility, particularly in response to climate change. The average height of populations - indicative of their nutritional and health status - deteriorated during the shift to cultivation. Threats to health came from the easier spread of infectious disease to unexposed - and thus susceptible - populations, by warriors, merchants, missionaries and explorers. Dramatic reversals in population growth sometimes followed contact between civilisations. The social environment exerted its influence in myriad ways, from the lead-based wine sweetener popular with the Romans - which may have signalled the decline of Rome through reducing fertility and deranging the aristocracy - to the motor car, and its first British victim, Bridget O'Driscoll, whose death in 1896 the coroner hoped would be the first and last of its kind.
The accelerating manner in which humans can permanently change the world they live in is the focus of a major section of the book, which builds on McMichael's previous work, Planetary Overload . The rise of greenhouse gases, ozone depletion, disseminated persistent organic pollutants and the loss of biodiversity feed into our uncertainty regarding the future. Here the metaphor of the "ecological footprint" is introduced - how does the tread of each member of the earth's population reverberate around the world and echo into the future? The giant ecological clodhoppers of the West are contrasted with the lighter step of the South - but, it seems, the economies that can afford the huge boots can also direct global policies that legitimise as much trampling as is desired.
World ecology may, if allowed to progress in unregulated fashion, come to illustrate what Garrett Hardin famously called "the tragedy of the commons".
That which is collectively owned is not collectively maintained, since the maximum immediate rewards are experienced by whoever is most exploitative - the freeloader problem. Sustainability thus requires a collective solution to a collective problem, since working towards it may be an irrational individual act - for the person or individual country. To attempt to cover the history, geography, biology and evolutionary significance of human health, and provide convincing future scenarios, takes a brave author with an unusual breadth of knowledge. McMichael shows that he is up to the task in this book, which will become a benchmark for discussions of global public health.
The case he advances does not pass unchallenged, however. Bjørn Lomborg's The Skeptical Environmentalist offers a very different picture of our current and future state. The ways in which the scenarios offered by these authors play out will determine whether the 21st century is characterised by further health gains or disastrous reversals.
George Davey Smith is professor of clinical epidemiology, department of social medicine, University of Bristol.
Human Frontiers, Environments and Disease: Past Patterns, Uncertain Futures
Author - Tony McMichael
ISBN - 0 521 80311 X and 00494 2
Publisher - Cambridge University Press
Price - £45.00 and £15.95
Pages - 413
