Appropriately in this time of plague, the capital’s Victorian cemeteries have proved a haven for appreciating this extraordinary best of springtimes. The most magical, long neglected until recently, Nunhead Cemetery in South London, is a woodland paradise – cow parsley and intensely blue borage everywhere, suffused by pungent wild garlic and echoing to the sounds of blackbirds and woodpeckers. Magnificent specimens of beech, oak, lime, plane and sycamore soar heavenward, their freshly minted leaves swaying gently in the breeze. And marvellous to behold, from the cemetery’s highest point Christopher Wren’s magnificent St Paul’s can be seen in the distance, seemingly alone and framed by an avenue of trees.

Amongst the ruined angels and broken pediments, the still discernible gravestone epitaphs convey the Victorians’ untroubled faith in an afterlife, a necessary consolation for parents grieving the loss of their children from prevalent infectious childhood illnesses. That mortal threat to the young and innocent has long since receded, defeated by the science of antibiotics and immunisations. Still, the shock of the Covid-19 pandemic necessarily poses anew the perplexing question for so many as to the role of microbes – bacteria, fungi and viruses – in the Grand Order of Things.

The common perception is that they are “germs” with no rationale other than to compound human suffering. Despite being the simplest forms of life they are remarkably efficient in doing so, disseminating themselves with impressive efficiency, periodically changing their antigenic spots to elude the immunological mechanisms nature provides to protect against them. By this account microbes epitomise that “blind, pitiless indifference” which Richard Dawkins insists “we should expect if there is no design or purpose, no evil and no good”.

Bernard Dixon, a former editor of the New Scientist, argues otherwise that microbes are indispensable to the emergence and flourishing of all “higher” forms of life. They are, he points out, in his Power Unseen; How Microbes Rule the World, as essential as the sun for the food we eat, both from plants and animals. Plants require nitrogen to grow, but its major source from the air cannot be utilised until “fixed” by bacteria in the soil and rendered soluble in water. Those “fixers” are bacteria: cyanobacteria in the rice-growing paddy fields of Asia, numerous species of rhizobia in the fertile fields of Europe, azospirillum in the grasslands of South America. Similarly sheep, goats and cows could not exist on their herbivorous diet were it not for the bacteroides and ruminococci in their ruminant stomachs, fermenting the indigestible cellulose of grass and leaves into digestible cuds.

The yeast saccharomyces converts sugar to alcohol and carbon dioxide giving us the staples of bread, wine and beer. The fungus Penicillium roqueforti gives us Roquefort and Stilton – so a meal of steak, chips, salad and cheese with a bottle of claret is entirely “germ dependent”. As indeed is its digestion, for without the tens of millions of bacteria in our colons we would generate astonishing litres of methane and hydrogen gases, whose elimination would require humans to be eructating and passing wind almost continuously.

In the ceaseless cycle of life, growth is balanced by decay that must in turn be recycled, and here, Dr Dixon tells us, microbes “make a massive contribution” transforming waste into compost, “rendering the cocktail of filth that arrives in a constant stream at sewage disposal plants safe and innocuous enough to be discharged into the cleanest of rivers”. And for good measure germs also eliminate pests, protect the ozone layer and counter global warming.

Meanwhile, the hundred trillion microbes that colonise our skin, gut and mucous membranes keep us healthy in a multiplicity of ways only recently appreciated: boosting the immune system, preventing the allergic conditions asthma and eczema, regulating the bowels and protecting against other pathogenic bacteria.

The putative merits of viruses are more difficult to discern; though, as recently observed, “many are clearly mutualistic, conferring on their host a fighting edge in the competitive world of nature”, having a unique ability to incorporate their genes into those of infected cells.

The defining feature of microbes is their adaptability, flourishing in the most hostile of environments – they can be found in the heart of bubbling volcanoes and buried deep in the ice of the Antarctic. In some instances their flourishing is clearly beneficial, indispensable to our very existence; in others, as a cause of infectious illness their predilection for the lungs or the skin or the meninges can be fatal. But the harm they cause is the inevitable corollary of their ability to do good. Not “blind, pitiless indifference” but a reflection of the unfathomable complexities of the natural world.

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