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Human frontiers, environments and disease

Book review, Financial Times

Human frontiers, environments and disease, by Tony McMichael, CUP 2001

There are many ways of looking at history, but the relationships between the evolution of our species, that of the micro-organisms in and around us, and changes in the environment have scarcely been explored. Until recently few realized the degree to which we depend on friendly bacteria and parasites. Without them we could neither breathe nor digest our food. Indeed our bodies contain many more bacterial than human cells.

In this book Tony McMichael brings alive this fascinating dimension of history. The co-evolution of humans and their micro-organisms over the last few hundred thousand years can be traced not only through their DNA, but also through varying patterns of human behaviour and diseases. In the age of hunter gatherers, it was the switch from a largely vegetarian to a largely carnivorous diet which exposed humans to animal bacteria and parasites. Their move out of Africa to new environments and climates reshuffled the pack. The adoption of agriculture and animal husbandry in crowded living conditions, often in close association with animals, reshuffled it again. Urbanization, and expansion into new environments, did so too. In the last two thousand years or so, there has been an equilibration in which different civilizations swapped microbes, often with devastating effect: witness the holocaust in the Americas in the 16th century, when empire-winning smallpox and measles dramatically reduced the indigenous population. Now we face new hazards produced by industrialization and the drastic changes we are bringing about in the planetary environment.

We often congratulate ourselves on our inventiveness. But bacteria and viruses are clever too. Their versatility is manifest in influenza, tuberculosis, malaria and HIV/AIDS. The story of chicken pox is a good illustration. The virus can run out of immediately susceptible individuals. To survive it can surrepticiously take cover in the nervous system of infected people, beyond the surveillance of their immune systems, and remain there for decades. It can then migrate along the neural network, and sensitize patches of skin. Shingles is the result. By scratching the consequent lesions, we do the virus a service by spreading it into populations which by then contain new susceptible individuals. The cycle is then complete. Much human ingenuity has been devoted to coping with the whole range of infectious diseases. Recently it was thought that we had almost succeeded. Now we know better. Micro-organisms are our other half.

What then of the future? We are moving into territory less charted than any imagined by our ancestors. In biological terms the enormous increase in the human population, from 2 billion in 1930 to over 6 billion today, can be regarded as a malign maladaptation by a species which, like rabbits in Australia, has escaped from natural control. We press heavily on the Earth's natural resources of land, water and other materials; we are changing the chemistry of the atmosphere and promoting climate change; we are destroying other organisms at rates reminiscent of earlier extinctions of life. Within the human population there are also huge changes. Over half of us live in cities, which are particularly liable to infection. The gap between rich and poor countries is getting wider, with the age profiles in each very different. Deterioration of environmental conditions in many parts of the world will increase pressure for major international migration. Yet in spite of these prospects most of us still adhere to a philosophy of consumerism, primacy of market forces, and the technological fix.

McMichael examines one by one the various threats to our welfare and their medical implications. Food supplies are clearly critical. We are what we eat. At present the system is out of kilter, with unsustainable methods of production in industrial countries, and severe and growing shortages elsewhere. This cannot be separated from current dependence on fossil fuels. In Britain the amount of fossil fuel required to produce, process and distribute the average person's annual food intake is about six times greater than the energy content of the food itself. The remedy of genetically modified food species carries many hopes but as many possible risks, including changes in the microbial population. We need to look again at conventional economics, and to establish true costs, not only of what we eat but of the impacts, medical and environmental, of industrial society. Like Amory Lovins, McMichael supports the notion of a natural capital of resources, whereby humans live on the interest, and avoid drawing down or debasing the capital itself.

As he says, "We have … passed through the 20th century knowing that our planet is but a peripheral speck in a vast and violent universe …Newtonian physics suffices to plan moonshots and to help pedestrians avoid being hit by a bus, but Einstein, Bohr and Heisenberg have shown us the surprising relativities, non-linearities and uncertainties of the cosmic and atomic worlds." In no area is this more true than in the relationships between animal and microbial populations, and in their reactions to a changing environment, in which human activity is an increasingly dominant factor.

Here is a book to make us think differently. Even if there are a few contentious points (for example about the scrapie/BSE relationship) and some repetition from time to time, it is a clear, lively and elegantly presented argument of wide scope in which unfamiliar issues are neatly put together. It is a tract for our times.

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