Diseases and Human Evolution

  • Ethne Barnes
University of New Mexico Press: 2005. 484 pp. $29.95 0826330657 | ISBN: 0-826-33065-7

The widespread resurgence of infectious diseases since the 1970s has stimulated many books about this ancient scourge. Following the lightning strike of HIV/AIDS in the early 1980s and its subsequent spreading wildfires, our sensitivity to threats from the realm of infectious disease has been reawakened. The many recent strikes, mostly from viral respiratory diseases, attest to the rising activity of ever-opportunistic microbes in an interconnected and rapidly changing modern world.

This book by the palaeopathologist Ethne Barnes traces the long history of human infectious diseases. Ever since humans first settled in villages, a succession of microbes, mostly animal-derived, have adapted to this auspicious medium. Some have become endemic infections; others make occasional forays from animal sources and may trigger devastating human epidemics. Patterns of infectious disease have changed kaleidoscopically as our forebears' culture evolved from agrarianism to nineteenth-century industrialization. Today we generate ecological niches for microbes through intense food production, greater human mobility, crowded peri-urban poverty and modern medical manoeuvres, such as transfusion and transplantation.

Barnes has digested a voluminous scientific literature and gives an orderly, well-written and comprehensive account of the topic. For a succession of types of infectious disease, she discusses origins and sources, genetic adaptations (of both microbe and human), microbial biology, population-health impacts, clinical features and, in some cases, control policies. The 23 chapters are approximately chronological, encompassing the parasites that first travelled with post-australopithecine hunter-gatherers, the revolution in human–microbial relations ushered in by farming and the consequent rise of various human-adapted infections (malaria, schistosomiasis, trypanosomiasis, tuberculosis, leprosy). Then there's the amplification of infectious diseases by urbanization and, in recent centuries, their spread by seafaring empires. Dramatic epidemics have occurred along the way — Europe, for example, has suffered from the bubonic plague (especially the fourteenth-century Black Death) and syphilis. In the crowded squalor of early industrialization, whole populations, and especially the urban poor, were ravaged by smallpox, cholera, tuberculosis, measles and other infectious diseases. In today's world, influenza is going global; many new infectious diseases are emerging, including HIV/AIDS and severe acute respiratory syndrome (SARS); and surprises have arisen such as Britain's mad cow disease and its human version, variant Creutzfeldt–Jakob disease.

The word ‘disease’ in the book title is somewhat misleading. Barnes accords little space to non-infectious diseases and, even then, the brief discussions of asthma and other immune disorders, heart disease, diabetes and various cancers tend to highlight the possible contributions of infectious agents. Indeed, the writing here is less enthusiastic and engaged than it is in the author's favoured microbial heartland. Certainly, until early last century the great bulk of (non-violent) deaths everywhere were due to infections and starvation. But today well over half the world's deaths are due to non-infectious diseases. And there is an expanding literature on how the biological legacy of human evolution predisposes us to many of those non-infectious diseases, especially as the living conditions in today's societies deviate ever further from the formative conditions of pre-agrarian life. Maybe there is another book to be written, to round out the story.

The author invokes the discomfiting military idiom that permeates much of the writing about this topic: chapter 2 is titled ‘The war between microbes and men’. This language was adopted early in the basic public-health models of infectious disease — in which researchers estimate ‘attack rates’ and talk about targets, microbial enemies and defence mechanisms. Modern molecular biology has embellished the idiom with notions of molecular missiles, antigenic camouflage and so on. However, this ‘us against them’ perspective can distort our understanding of the evolutionary basis and ecological complexity of infectious-disease transmission and virulence. In the rapidly changing world we live in today, we need a greater understanding if we are to lessen, proactively, the risks of new infectious diseases arising. Defensive reactivity — although it is necessary — will not be enough.

There is much interesting detail in this book. The opening chapter sets the stage well, discussing how the intertwined stories of cultural and genetic evolution are fundamental to the emergence and spread of infectious diseases. The book's narrative would have been enriched by a more explicit exploration of these unifying threads throughout. All too briefly, and therefore superficially, the final several pages consider the high-risk path that we humans are now following. In a “crowded world” that is “out of order”, more attention must be paid to how infectious disease may cut swaths through increasingly vulnerable populations in a world of rising microbial mobility.