Great men don’t shape history – but tiny microbes do

On Tuesday afternoons, pathology teaching at medical school required me to peer down a microscope for two hours, screwing my inactive eye ever more tightly shut as if that would make the looking eye suddenly see clearly. Each eosin-stained slide with its pink and purple lines and splodges of diseased cells was as legible to me as a barcode. The tiny world beneath my lens created an illusion of human supremacy, a world where the truth was small, immobilised and bored of itself.

Pathogenesis – the cause of disease, its development and the impact it has on cells and organisms – is thankfully not what Pathogenesis is about. Jonathan Kennedy is a sociologist, not a microbiologist, and his unit of interest is the epidemic event, not the single bacterium. Where tales of great white men, great inventions and great power once populated the history books, Kennedy argues that great plagues are what really matter. Immunity has been the unifying asset of survivors and victors. The historical sweep of his pen could not be wider, from pre-history to post-Covid. Three hundred-odd pages roam through 50,000 years, and by the last it’s almost impossible to disagree that infectious diseases are our permanent companion and ultimate adversary.

Humans are not always in competition with pathogens, though. In fact our existence is indebted to them. A viral infection hundreds of millions of years ago might have enabled our brains to form memories, because of the insertion of a heritable piece of DNA that codes for ‘tiny protein bubbles’ to assist information transmission between neurons. Moreover, the fact that we’re not nibbling at the shells of our mothers’ eggs is because ‘a shrew-like creature developed the capacity to gestate her young inside her own body’. Thanks to a retrovirus, mammals were gifted the placenta and the relative safety of pregnancy.

As possibly the only person not to have read the 2014 mega-hit Sapiens, I was intrigued by the more speculative sections of deep history on different human species.