Diseases and Human Evolution

1: Introduction

CHAPTER 1 Introduction Recent interest in new diseases, such as HIV/AIDS and Ebola, and the resurgence of older diseases, such as tuberculosis, has raised important questions about the history of human infectious diseases. How did the various infectious diseases evolve? Where did they originate? What factors have hindered or facilitated diseases? How does a microorganism become a disease -causing agent (a pathogen)? Have infectious diseases changed through time? What can we do to prevent diseases from occurring and recurring? In an attempt to answer these questions, many books and articles have been written over the years, some quite recently, from different viewpoints. Some writers have focused on the historical perspective of major diseases affecting civilization. Others have focused on the evolution of specific diseases from a medical approach. Some discuss the interaction between human behavior and the evolution of certain human diseases. This book brings together the various viewpoints in a multifaceted approach to the issues. Human beings are unique in that we have evolved not only biologically , like all other creatures of this Earth, but also culturally. Changes in human behavior patterns with cultural evolution throughout the millennia have had the greatest impact on the evolution of human diseases. The study of human beings and their behavior through time, the province of anthropology , gives an objective perspective of how human behavior patterns and attitudes have influenced the evolution of human diseases. 1 The Meaning of Disease The very word disease implies discomfort, or lack of “ease,” within the body. Whenever the functioning of the body or any of its parts becomes impaired, disease occurs. Sometimes the impact of disease can be very minimal, while at other times it can be incapacitating and life-threatening. Most human diseases are caused by microorganisms from our environment, and human behavior patterns frequently influence how these microorganisms are spread. Current perceptions of disease and its causes have roots in earlier belief systems; such perceptions also vary throughout the world. How people view their diseases depends upon how their culture interprets what constitutes a disease, and there are many different cultures with differing ideas about disease. Modern Western medicine views the physical signs of disease as a biological process with a specific biological cause, while healers in other parts of the world may see the same physical signs of disease as the result of an imbalance within the body or with nature, a supernatural process, invasion by foreign substances, sorcery, or punishment for violation of rules governing human behavior (Murdock 1980). Not all human diseases are universally recognized as diseases. In areas where it is common to find the majority of the community afflicted with the same health problem for generations, people frequently accept the problem as part of their natural existence. This is common among peoples infested with parasites in underdeveloped countries , and among peoples suffering with goiters for lack of iodine in their soils, as in the highlands of Ecuador and Papua New Guinea. The biological interpretation of disease in modern nations, developed by Western European civilization, rests on the premise of specific etiology (Dixon 1978). The European germ theory developed during the seventeenth century emphasizes specific causes for specific infectious diseases. Cure is obvious: just eliminate the causative agent by using medicines, surgery, radiation , or other intervention measures. Modern public health measures employed to prevent disease follow the same premise of using tactics designed to attack specific germs that can invade water supplies, food sources, and living and working areas. Indeed, many infectious diseases that frequented our communities in the past have been greatly reduced or vanquished through public health measures and better standards of living. However, overzealous sanitizing of modern environments , water, and food sources can undermine natural human immune 2 CHAPTER 1 responses, leaving the seemingly protected population vulnerable to invading microbes able to sneak past the protective barriers. The germ theory led to the antibiotic era that began in the early 1950s, dramatically reducing the threat of serious bacterial infections. Unfortunately, overuse and misuse of antibiotics in medical treatment and in animal feeds over the years has caused more harm than good, as the targeted microorganisms have figured out how to resist these drugs. The “miracle” antibiotic drugs were never effective against viral infections ; they could only be used against bacterial infections. The “miracle” drugs were oversold to the public to “prevent” secondary bacterial infections following...