How stripy are tigers?

Tim Lewens

  • BuyUnsimple Truths: Science, Complexity and Policy by Sandra Mitchell
    Chicago, 149 pp, £19.00, December 2009, ISBN 978 0 226 53262 2

The world is a complex place. That is a truism, but perhaps complexity can be investigated rather than taken for granted. Think of the sorts of causal interaction one might regard as ‘complex’. In 2002, Avshalom Caspi and collaborators published a widely reported study in which they concluded that the degree to which abuse in childhood increases the likelihood that men will exhibit antisocial behaviour later in life was partly dependent on the presence of a gene that appears to control the activity of an enzyme called monoamine oxydase A. Or consider an article published by the British Journal of Cancer in February, which suggests ‘the intriguing possibility of a causal link between the molecular basis of breast cancer exemplified by p53 mutations and extreme deprivation’. Mutations in the p53 gene reduce the body’s ability to suppress tumours: what is ‘intriguing’ here is the thought that poverty might interact with the gene in question, thereby worsening the prognosis for economically deprived cancer patients. Some studies have suggested that socioeconomic inequality somehow causes poor health – even among the reasonably well-off in unequal societies. These assertions of causal links between very different sorts of things – poverty and genes, inequality and health – are often contested, but they aren’t especially unusual.

We see interactions across causal levels: poverty affects the activity of genes. We see probabilistic contingency: poverty does not guarantee a lower breast cancer survival rate, it merely makes it more likely. We see contextual contingency: the probabilistic boost that a particular gene gives to one’s chances of manifesting antisocial behaviour depends on how one was treated as a child. We see feedback loops across multiple causal levels: inequality is a population-wide phenomenon that affects the health of individuals within it. Health, in turn, affects economic productivity and alters the socioeconomic profile of the population. Finally, there are aspects of complexity not captured by these examples, such as ‘chaotic contingency’. Change the initial conditions of a system by a barely perceptible fraction and its fate is altered radically.

Sandra Mitchell’s Unsimple Truths – a translation of a book originally published in German as Komplexitäten: Warum wir erst anfangen, die Welt zu verstehen – attempts to trace these contours of complexity. Five of its six chapters focus on Mitchell’s own discipline, philosophy of science, revising traditional accounts of how the sciences, and the world they investigate, work. She builds towards a general vision of scientific practice she calls ‘integrative pluralism’, which recognises not only the complexity of the world but also the complexity of the sciences’ relationships to each other. Refreshingly, she also steps beyond the conventional boundaries of the philosophy of science, devoting a chapter to reflections on how policy-makers should deal with complexity. Some sciences have the luxury of investigating model systems, such as those friction-compensated surfaces on which the school physics student’s toy car can be subjected to an allegedly uniform acceleration. But the policy-maker needs to plan and intervene in the world as we find it, not treat it as an artificially controlled system. How can one plan in a world whose causal structures are multilayered, and whose future is so dependent on contingencies?

Traditional philosophy of science, as Mitchell sees it, suffers from two lifestyle conditions. First, it has an unhealthy diet: too many examples from physics. If we paid more attention to psychology, biology and so forth we would see the error of trying to squeeze all of scientific practice into a model built for one subdiscipline. Second, it doesn’t get out enough: it spends too much time in the armchair. Philosophers have tended to study how science works by putting together formal models which are overly reliant on logic and abstract reflection on imaginary examples, and insufficiently sensitive to the details of what scientists do and to the nature of real processes. Both of Mitchell’s remedies – move the focus away from physics, use real cases from science – are characteristic of much fashionable work by ‘naturalistic’ philosophers of science, who tend to regard science as ‘the best source of knowledge of nature’; the remedies are valuable, but their virtues can be exaggerated. Philosophy, too, is a complex business.

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