Synchronicity. The meaningful coincidence of causally unrelated events. It was the Swiss psychologist and all round weaver of the wind Carl Jung who coined the word. No doubt the old mystic had greater quarry in mind than my holiday reading when he fashioned the concept – evidence no doubt of our collective unconsciousness – but the unanticipated dialogue between some of the books I took away with me this year added considerably to the pleasure in reading them. At first sight, EO Wilson’s ‘The Diversity of Life’ and Daniel Callahan’s ‘False Hopes: Overcoming the Obstacles to a Sustainable, Affordable Medicine’ are not obvious bedfellows. Wilson’s is a now legendary meditation on the almost inconceivable richness of biological life and the mortal peril that we human’s are exposing it to. Callahan warns us, by contrast, that the immortal longings that currently drive medicine will only lead to frustration in the face of inevitable decline and death. Medicine has set its sights on goals technologically unrealisable and economically and emotionally unaffordable.

Sustainability was only the first and most obvious of the links between the two. Callahan writes from the States. American health care, probably the most inequitable in the developed world, is also the most expensive. Its costs hamstring the economy and even medium term it looks like the system is unsustainable. How can its costs be reined in? According to Callahan only by chastening the desire for maximal health and extreme longevity, for longer and healthier life at all costs. Environmentally, the sustainability argument has long been won, in theory if not, tragically, in practice and Wilson, no sentimentalist, argues in support of strip logging in his beloved rain forests – if you log in strips up hillsides, the untouched forest seeds what has been denuded, and the nutrients from successive strips wash down to feed the new growth. Biodiversity thrives, and the owners of the forest enjoy a sustainable income.

Interestingly though both writers were also, in their very different ways, engaged in a deeper debate about that wonderfully multiple and elusive thing we call nature. Difficulties stem, for both writers, because we have set ourselves in opposition to it. For Callahan we are at war with our own nature, for Wilson the war is being waged with external nature – ‘human hunters’, he says, ‘help no species.’ For Callahan a sustainable medicine is only possible if we are willing to accept the limits our biological nature sets us. There are two aspects to this. We need to recover our respect for the old tradition of Hygeia . Hygeia was the Greek goddess of health. Her father, Asclepius, was the god of medicine. For Callahan we have become too dependent on the spirallings costs of technological, Asclepian medicine. It desperately needs counterbalancing with Hygeia’s insights that, given the right circumstances, health is the body’s natural state of equilibrium. Surely, Hygeia would argue, the cure for obesity lies not in the surgeon’s hands but in exercise and the regulation of the appetite. Industrial medicine, it follows, must be tempered by the neglected tradition of public health. Callahan also draws on a concept of nature for the second of his arguments. Rather than hurling money in a desperate attempt to push back the frontiers at both the beginning and end of life, we need to accept that illness and death are inevitable. Medicine must accept the human lifecycle, not ceaselessly fight it. Is it really ethical, he asks, to invest so much money in the search for a few more months of life when death will come whether we want it or not? Better by far to spend our resources on ensuring that as many of us as possible achieve an ordinary life rather than scrabble around to draw out the dying organisms last days. We have a biological nature, he suggests, so let us accept it.

Wilson on the other hand wants us to recognise our absolute dependence on the biological diversity of the nature that surrounds us. By annexing all moral value to human life, by seeing the natural world as exclusively a resource, an instrument, we have laid it waste. If we push it much further it will collapse, taking us with it. Yes nature has instrumental value for us – think only of the pharmacological riches lurking undiscovered: millions of species, millions of evolving biochemical adaptations to shifting environments – what lab could hope to replicate it? But a new relationship is necessary – not tyranny and plunder but husbandry and respect.

Like Wilson we should avoid sentimentality. For thousands of years we have fought for our lives against the casual horrors of nature. Even now – the AIDS virus, the anopheles mosquito – who would mourn their eradication? And medicine, increasingly, is one of the most powerful weapons in our arsenal. Yet both these books suggest that the legacy of that long struggle with nature is a relationship that no longer serves us. Bring us back into balance, they differently argue, Hygeia with Asclepius, instrumentality with a recognition of dependence.

Julian Sheather is ethics manager, BMA. The views he expresses in his blog posts are entirely his own.