Disease Selection: The Way Disease Changed the World

By Roger Webber

Diseases have had more influence on us than we realize. They have taken a major role in making us humans and probably determine the way we run our lives. They emerged with us from our ancestral home in Africa, to spread to the rest of the planet. History is full of the great epidemics of plague, smallpox and anthrax, with the present catastrophe of HIV that is changing the demography of the world in a similar way to its predecessors. We survived because of our genetic variation and immune system and it will be this that will save us again.

So fundamental has been the part that disease has played in the world that it has brought about change, just as much as has natural selection. Actually disease has been another force, sometimes acting with natural selection but often in opposition. It continues to have a far more profound effect on all of us than realized, selecting the course of the world just as much as nature has.

• Language: English
• Publisher: CAB International
• Release date: Oct 28, 2015
• ISBN: 9781780646855

Roger Webber

Roger Webber grew up in East Africa which gave him early exposure to travel to foreign countries. He qualified in medicine and worked in the Solomon Islands for the next ten years, during which he undertook research that led to a programme of eliminating filariasis from the world. He was posted to Tanzania as a Medical Coordinator of an aid programme and completed his second travel book. In 1985 he joined the London School of Hygiene and Tropical Medicine where he made extensive visits to Asia resulting in the book’s title.

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Disease Selection

The Way Disease Changed the World

Dedicated to Brian Southgate (1930–2011), my mentor and a great teacher, with whom I shared many of the interests contained in this book, which he would have loved to write if he were still with us. As a tribute I make him my posthumous co-author.

Disease Selection

The Way Disease Changed the World

Roger Webber

CABI is a trading name of CAB International

© R. Webber 2015. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners. Figures in the public domain are excluded from this restriction.

A catalogue record for this book is available from the British Library, London, UK.

Library of Congress Cataloging-in-Publication Data

Webber, Roger, author.

Disease selection : the way disease changed the world / by Roger Webber.

p. ; cm.

Includes bibliographical references and index.

ISBN 978-1-78064-682-4 (hbk : alk. paper) -- ISBN 978-1-78064-683-1 (pbk. : alk. paper)

I. C.A.B. International, issuing body. II. Title.

[DNLM: 1. Communicable Diseases--history. 2. Host-Pathogen Interactions. WC 11.1]

RA643

362.1969--dc23

2015020429

ISBN-13: 978 1 78064 682 4 (hbk)

             978 1 78064 683 1 (pbk)

Commissioning editor: Caroline Makepeace

Assistant editor: Alexandra Lainsbury

Production editor: Tracy Head

Typeset by SPi, Pondicherry, India.

Printed and bound in the UK by CPI Group (UK) Ltd, Croydon, CR0 4YY.

Contents

List of Illustrations

Preface and Acknowledgements

Introduction

1 The Sexual Revolution

2 Out of Africa

3 Host/Parasite Interaction

4 Using a Vector

5 The Great Plagues

6 Missionaries of Death

7 The Slave Trade in Parasites

8 Eden’s Garden of South America

9 A Glass of Water

10 The Great War

11 Man’s Best Friend?

12 The Animal Connection

13 Not Clean

14 Too Clean

15 The Food We Eat

16 Cancer

17 Climate Change and Population Movements

18 Disappeared and Emergent Diseases

19 The Future

20 Conclusions

Resource Material and Suggested Further Reading

Index

About the Author

List of Illustrations

Preface and Acknowledgements

Diseases have been brought very much to the fore with the Ebola crisis, the recent epidemics of influenza and the more protracted concern of antibiotic resistance. It is as though the problems of communicable diseases have come out of the cupboard to haunt us again. They were something of the past, within our ability to control and not something we need unduly concern ourselves with. This, however, has never been the case, as they have always been a problem in the developing world, where such diseases are an everyday fact of life. Just to survive malaria and diarrhoea has been a battle that most children have had to fight, while HIV (human immunodeficiency virus) and tuberculosis are an ever-present threat to the adult. Much progress has been made and it is certainly a healthier world than when I first started out as a young doctor, but communicable diseases are still an ongoing concern.

When a current crisis is over we can put the problem of disease out of our minds. However, this is not what diseases are, something alien that comes to trouble us every now and then. They are part of our lives and, as will be seen further on, such an intimate part of us that they have more influence in our lives than we realize. They have taken a major role in making us humans and probably determine the way that we run our lives. To show this I have needed to start from the very beginning, from when life started, then as we emerged from our ancestral home in Africa, to carry our complement of diseases to the rest of the world. There followed the great epidemics that changed the history and demography of the world, which we survived because of our genetic variation and immune system.

So fundamental has been the part that disease has played in the world that it has brought about change, just as much as has natural selection. The purpose of this book is to show that disease has actually been another force, sometimes acting with natural selection but often in opposition; this is why the book is called Disease Selection. Appreciating the intimacy the disease process has with us allows for a greater understanding of its effects, enabling us to take preventive action and live healthier lives. If some of this happens then much of the objective of this book will have been achieved.

In order to cover the subject in breadth I have had to branch into fields of evolutionary biology, archaeology, history and others, in which at best I can only be an informed amateur. My resources have been the books by experts in the field and the boundless limits of the Internet. Even in just the medical literature, the number of references for each fact would be enormous, but taking in all the other subject areas, this is quite beyond the realities of compilation. I have attempted to list the main books and web sources used and many of the references will be found in them, with just a small number of the key scientific papers included in the resource material. This in no way reflects my lack of recognition for the considerable contribution by all the many who have advanced their fields of science. I hope they will forgive me for not quoting all their work in full. They have been a most valuable resource, for which I am very grateful.

I owe a particular debt to David Bradley for kindly going through sections of the manuscript and saving me from several errors. He has added considerably to my understanding of the processes of communicable diseases in the many years I have known him and I thank him for his continuing help. I apologize if I have still not got everything right, the fault for which lies entirely with me.

I would also like to thank Claire Allum for helpful discussions in archaeology and on the people of Africa. The origins of humans make up an ever-changing and controversial field, and her guidance in this has been most valuable, although many of the views remain my own. Everild Haynes has been the most excellent editor, not only in considerably improving the script but in adding her expertise in plant metabolism.

I am most grateful to CABI, the publishers of my textbook, who have allowed me to use several illustrations and tables from it, as well as offering every encouragement for this present work. This type of book is a new venture for them and I appreciate their confidence in me. For the other illustrations, I would like to thank the World Health Organization for permission to use Figs 4.4 and 7.3, Her Majesty’s Stationery Office, London, for Fig. 1.2, Brainpicking.org for Fig. 7.2, and the Izikio Museum, Cape Town, the National Gallery of South Africa and the Blombos Museum of Archaeology for permission to take the photographs in Fig. 2.1. These and the other illustrations are provided freely for general use and as such are not covered by any copyright restrictions of this book.

Introduction

When Charles Darwin, with the often forgotten contribution of Alfred Russel Wallace, formulated the theory of evolution, it was the concept of natural selection that was to revolutionize an idea that had been discussed for some considerable time. The process of evolution had been understood, with the attempted explanation of Jean-Baptiste Lamarck (1744–1829) and even that of Erasmus Darwin, Charles Darwin’s grandfather. But it was the paper written by Wallace on the island of Halmahera that, when it reached Darwin, galvanized him into action to elucidate in detail the theory that had been developing within him ever since his famous voyage on the Beagle, and resulted in the publication of The Origin of Species by Means of Natural Selection in 1859.

Darwin and Wallace had realized that multiple forms of creatures had been produced, but only those best adapted to the place and conditions in which they lived were successful and survived. Every place had specialist conditions, such as a particular food source, so that individuals would develop that were most suited to exploit this resource. These individuals would reproduce and the most successful of their offspring would fill this particular niche or expand into similar conditions under which they were more suited than the present occupants.

The development of modified individuals took place by a process of mutation in which changes to the genetic make-up would randomly occur. Many times these mutations were a disadvantage and the individual would not survive, but occasionally an improvement would arise that made the new individual more successful. Over considerable periods of time, small sequential improvements appeared to take place, although in reality they were a very extensive process of trial and error. In addition, during periods of stress, greater change has been found to happen due to the action of transposons (jumping genes), which greatly accelerate the process and often seem purposeful.

The natural environment would also change over long periods of time, new food sources would develop and circumstances improve or diminish, so that as these conditions changed then more suitable individuals would evolve to displace those that had been there originally. A new plant would originate that a new animal would find more edible or a prey animal would develop a defensive mechanism that protected it from its predator. Evolution was a continual movement; as one species changed it became more (or less) suitable for another species that fed on or otherwise benefited from it, and so the second species changed as well. Species were not fixed but changed over periods of time. Some were surprisingly successful, like members of the crocodile family that have remained in a similar plan–form for millions of years, while others, such as the flightless Dodo, were no match for a rapidly changing environment and went extinct. In our rocks are to be found the fossilized remains of an incredible range of animals that were at one time successful, and sometimes extremely successful, like the trilobites, but in their turn were not the best suited for the prevailing conditions, and so became extinct.

Life then was a competition to be won by the fittest and most suited for the particular place and conditions. Success was judged not only by survival but the ability to pass on genes to the next generation. It might be the strongest male in a group of animals living in herds in which the dominant male had access to as many females as he could coral into his harem, such as with red deer, or the peacock with the largest and most beautiful tail that outshone his rivals. These were, however, risky strategies, as the dominant male in the herd would be challenged by rivals, who in time would overpower him, often with fatal consequences, and if the peacock had too large a tail it could not fly well enough to escape predators. A balance would therefore develop in which there was an amount of change that was the best fit for the purpose concerned, while at the same time not jeopardizing survival.

Darwin expanded upon the process in his second book on evolution published in 1871, The Descent of Man and Selection in Relation to Sex. The role of sex then became another process by which evolution took place, now generally known as Sexual Selection.

The term fitness is an all-encompassing term, to include the genetically most suited individual, with access to the best food source, as well as freedom from disease. A female bird will be able to tell from the sheen of the feathers whether a courting male has a burden of parasites, and a male herd animal obviously suffering from illness will not be strong enough to challenge the dominant male, so will be less fit. The contribution of disease can sometimes be out of all proportion to the other benefits that the individual may possess. The progeny may be the offspring of the best male and female in the flock or herd and brought up on the most advantageous source of food that its dominant parents can provide, but if it contracts an illness, this can put it at a disadvantage to its well, but genetically less suitable, rivals.

Changes in disease-causing organisms are produced in exactly the same way as the rest of nature is evolving, and provide a means for those organisms to dominate their environment. A parasitic organism is exploiting a niche by living on another organism, to its own advantage but to the other’s disadvantage. This needs to be a compromise because if the parasitic organism is too successful and kills the animal it is invading before it has been able to reproduce, then not only will it be robbed of its food source but also of its ability to survive.

With virus infections, the virus is not a free-living organism, but depends upon the cells of its host to continue its existence, so the inevitable consequence is the demise of the host, or for the host to be changed so considerably that it is at a disadvantage compared with a healthy rival. To overcome viral infections, animals developed immune mechanisms that were able to eliminate the disease so that the animal was only temporarily incapacitated, giving it a greater chance to survive long enough to regain its previous vigour. Immune mechanisms have also developed against bacterial infections, and bacteria are in most cases self-contained organisms. These mechanisms would have been developed first as bacteria were the earliest forms of life on our planet (but see further in Chapter 1). Immune strategies have been developed against infections by most of the larger parasites as well, for instance the nematode worms, but these mechanisms are more compromising in allowing the parasitic organism to continue to live within the host organism without producing sufficient damage to kill it.

We have developed a very comprehensive immune system that originated with the reptiles some 300 million years ago. Both plants and lower animals have immune mechanisms, but it was not until the reptiles, and the subsequent development of mammals, that the type of immune mechanism we now have was selected by evolutionary processes.

Illness caused by disease is either part of the process of natural selection or, in some circumstances, directly opposes it. In HIV infection, it directly opposes natural selection.

In humans, to pass on his genes, the man needs to successfully mate with a woman, and natural selection encourages the male to mate with as many females as he is able or is permitted to by the female. The social constraints of marriage and moral standards modify this, but in history there are many examples, such as Genghis Khan or the Ottoman sultans, fathering huge numbers of children. Even within the constraints of marriage, in many countries large families were or still are the norm, to ensure sufficient surviving children to continue the family line. However, the more females a man mates with in HIV-infected areas, the greater the risk he has of developing HIV infection, so becoming debilitated and in course of time (modified by chemotherapy), dying from the disease. In other words, the more successful he is in endeavouring to pass on his genes the greater the chance he has in dying from disease, so disease is selecting against him.

Even if, as one of the preventive actions of combating HIV, monogamy is practised, the tendency of natural selection is directly opposed by disease selection. In many African countries, the major victims of HIV infection are women, most of whom have been in monogamous relationships. This is because their male partners have strayed from the relationship, often consorting with a high-risk sexual contact, so that they become infected and subsequently pass the infection back to their partner. If the woman becomes pregnant, then her infant is also likely to become infected, further opposing the process of natural selection to produce healthy children.

When HIV infection was first recognized and before control methods had been developed, some highly successful individuals that would have been key people in the development of their communities were the first victims. Highly successful individuals are often highly promiscuous as well – this is natural selection in operation – but disease killed them off. Zambia was one of the first countries to feel the full effects of the HIV epidemic, which killed a large number of successful business people and managers at all levels of society. This was to have a profound effect on the country, as disease has had throughout the ages.

Disease is often viewed as a temporary inconvenience, something that can be treated, and after it has passed, life continues again as normal. Even in epidemic form, it might kill off large numbers of people, but there are still others to take their place, and when the epidemic has passed, it is largely forgotten. But disease has had and continues to have a far more profound effect on all of us than has been realized; it has selected the course of the world just as much as the rest of nature has, as will be shown in the following chapters.

The Sexual Revolution 1

Origin of Life

The general consensus is that life originated in the oceans some 4 billion years before present from the heat and nutrients of hydrothermal vents. Although the heat originated from volcanic processes and was intense, it was cooled by the surrounding ocean and a gradient of temperature was created that provided the ideal conditions for life to start. This first life was very simple, just a cell wall containing cytoplasm, and could quite easily have happened, as shown by Wagner in his book Arrival of the Fittest; it was termed a prokaryote.

All cell walls are made from amphiphilic lipids, which are so called because one end likes water and the other likes oils and not water. This property enables lipid molecules to be directionally arranged, a phenomenon that is seen if a thin film of oil is spread on to water, in which it naturally forms into globules, thereby separating the oily components from the water outside. This is thought to be how simple cell walls originated, to be subsequently improved upon by random mutations of their organic contents.

These mechanisms enabled the development of two early life forms, the Archaea and the Bacteria, which set about colonizing the planet. Bacteria are found on all surfaces and in every part of the earth, even within rocks and thermal springs that are too hot for any other form of life. They have been found as far as 5.3 km down a borehole in Sweden, and in hydrothermal vents where they survive on sulfate and hydrogen, while one species known as Deinococcus radiodurans is able, as its name implies, to survive high doses of ionizing radiation, as well as being dried out and subjected to intense ultraviolet light.

Our bodies are covered with bacteria, they are in every orifice and happily live within our intestines (Fig. 1.1), providing us with almost 15% of extra calories from our food. Bacteria were so successful and in such abundance that for several millennia they and the Archaea were the only forms of life on our planet, and there seemed no need for there to be any other. They were