Paul W. Ewald (born ) is an American

evolutionary biologist Evolutionary biology is the subfield of biology that studies the evolutionary processes such as natural selection, common descent, and speciation that produced the diversity of life on Earth. In the 1930s, the discipline of evolutionary biol ...

, specializing in the

evolutionary ecology Evolutionary ecology lies at the intersection of ecology and evolutionary biology. It approaches the study of ecology in a way that explicitly considers the evolutionary histories of species and the interactions between them. Conversely, it can ...

parasitism Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

evolutionary medicine Evolutionary medicine or Darwinian medicine is the application of modern evolutionary theory to understanding health and disease. Modern biomedical research and practice have focused on the molecular and physiological mechanisms underlying hea ...

agonistic behavior Agonistic behaviour is any social behaviour related to fighting, which can include aggressive behaviour, but also threats, displays, retreats, placation, and conciliation. The term "agonistic behaviour" was first defined and used by J.P. Scott ...

, and

pollination Pollination is the transfer of pollen from an anther of a plant to the stigma (botany), stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example bees, beetles or bu ...

biology. He is the author of '' Evolution of Infectious Disease'' (1994) and '' Plague Time: The New Germ Theory of Disease'' (2002), and is currently director of the program in Evolutionary Medicine at the Biology Department of the University of Louisville. Ewald is known for his theories on the evolution of virulence and his theory that many common diseases of unknown origin are likely the result of chronic low-level

infections An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

from

viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are found in almo ...

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

protozoa Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...

. Ewald contended with the conventional wisdom that a "well-adapted parasite is a benign parasite," pointing out that this idea relies on group selection, and instead suggested that low virulence is only selected for if the pathogen relies on host mobility for transmission.

Education and career

Ewald received his BSc in 1975 from the

University of California, Irvine The University of California, Irvine (UCI or UC Irvine) is a Public university, public Land-grant university, land-grant research university in Irvine, California, United States. One of the ten campuses of the University of California system, U ...

, in biological sciences and his PhD in 1980 from the

University of Washington The University of Washington (UW and informally U-Dub or U Dub) is a public research university in Seattle, Washington, United States. Founded in 1861, the University of Washington is one of the oldest universities on the West Coast of the Uni ...

, in

zoology Zoology ( , ) is the scientific study of animals. Its studies include the anatomy, structure, embryology, Biological classification, classification, Ethology, habits, and distribution of all animals, both living and extinction, extinct, and ...

, with specialization in

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

and

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

. He was formerly a professor of biology at

Amherst College Amherst College ( ) is a Private college, private Liberal arts colleges in the United States, liberal arts college in Amherst, Massachusetts, United States. Founded in 1821 as an attempt to relocate Williams College by its then-president Zepha ...

, and is currently director of the program in evolutionary medicine in the Biology Department of the

University of Louisville The University of Louisville (UofL) is a public university, public research university in Louisville, Kentucky, United States. It is part of the Kentucky state university system. Chartered in 1798 as the Jefferson Seminary, it became in the 19t ...

Ideas

Ewald asserts, along with a growing body of studies, that many common diseases of unknown origin are likely the result of chronic low-level

from

. For example,

cervical cancer Cervical cancer is a cancer arising from the cervix or in any layer of the wall of the cervix. It is due to the abnormal growth of cells that can invade or spread to other parts of the body. Early on, typically no symptoms are seen. Later sympt ...

can be caused by the

human papilloma virus Human papillomavirus infection (HPV infection) is caused by a DNA virus from the ''Papillomaviridae'' family. Many HPV infections cause no symptoms and 90% resolve spontaneously within two years. In some cases, an HPV infection persists and r ...

, some cases of liver cancer are caused by

hepatitis Hepatitis is inflammation of the liver parenchyma, liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes (jaundice), Anorexia (symptom), poor appetite ...

C or B and the bacteria ''

Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, Flagellum#bacterial, flagellated, Bacterial cellular morphologies#Helical, helical bacterium. Mutants can have a rod or curved rod shape that exhibits l ...

'' has been proven to cause

stomach ulcers Peptic ulcer disease is when the inner part of the stomach's gastric mucosa (lining of the stomach), the first part of the small intestine, or sometimes the lower esophagus, gets damaged. An ulcer in the stomach is called a gastric ulcer, while ...

. Ewald argues that many common diseases of currently unknown etiology, such as cancers, heart attacks, stroke and Alzheimer's, may likewise be also caused by chronic low-level microbial infection. Ewald disagrees with the popular theory that

genes In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

alone dictate chronic disease susceptibility. Ewald, whose background is in

evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes such as natural selection, common descent, and speciation that produced the diversity of life on Earth. In the 1930s, the discipline of evolutionary biolo ...

, points out that any disease causing gene that reduces survival and reproduction would normally eliminate itself over a number of generations. Ewald says that "''chronic diseases, if they are common and damaging, must be powerful eliminators of any genetic instruction that may cause them''." One example of this is

schizophrenia Schizophrenia () is a mental disorder characterized variously by hallucinations (typically, Auditory hallucination#Schizophrenia, hearing voices), delusions, thought disorder, disorganized thinking and behavior, and Reduced affect display, f ...

; patients with this mental illness rarely reproduce. Ewald argues that, just by evolutionary pressures, schizophrenia would have already been eliminated if its causes were strictly genetic; he suggests that in the future, an infectious cause of schizophrenia will be discovered. Ewald explains that purely genetic causes of chronic disease will persist only if a genetic instruction provides a compensating benefit (for example, the disease

sickle cell anemia Sickle cell disease (SCD), also simply called sickle cell, is a group of inherited haemoglobin-related blood disorders. The most common type is known as sickle cell anemia. Sickle cell anemia results in an abnormality in the oxygen-carrying ...

is caused by a genetic mutation that, in

heterozygote Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mos ...

s, protects against malaria, which kills millions worldwide each year). Further evidence for a non-genetic etiology of diseases like schizophrenia, Ewald also points out, comes from concordance studies on

identical twins Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two e ...

, which measure the percentage of identical twins who both develop a disease. A concordance of 100% indicates a primarily genetic disease, which is not really influenced by environmental factors like infection, nutrition, or toxins. Huntington's disease, for example, has a concordance rate of 100%, indicating a predominately genetic etiology. However, when the concordance rate is lower, this indicates environmental factors like infectious microbes or toxin exposure are playing a causal role. Schizophrenia's concordance is approximately 35-60%, suggesting, says Ewald, that microbes are etiologically involved. Another example is

breast cancer Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipp ...

: Ewald notes that in the case of

, when one twin develops

, the other twin has only a 10% to 20% chance of developing the disease, and this concordance rate of just 20% again indicates that environmental factors like infectious microbes or toxins are likely playing large causal roles in breast cancer. Ewald's curiosity regarding the

evolutionary Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certa ...

process of infections was sparked by a bad case of diarrhea he had in 1977. His first thought during this bout was that his body was using diarrhea to expel the

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

and he should avoid anti-diarrheal medication. Looking at the problem from the standpoint of the organism, expulsion was not an

benefit. The only benefit to the pathogen causing the sickness would be the potential transmission to other hosts; much like the particulate expelled during coughing, diarrhea can be a means of distribution. Another major influence on Ewald's thinking in evolutionary biology terms was the

HIV The human immunodeficiency viruses (HIV) are two species of '' Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the im ...

virus, which once caught, initially remains inactive for years thus allowing it to spread, before the chronic disease of

AIDS The HIV, human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a Preventive healthcare, pr ...

finally manifests, incapacitates, and eventually kills the host.

Awards

In 2010, ''

Utne Reader ''Utne Reader'' (also known as ''Utne''; , ) is a digital digest that collects and reprints articles on politics, culture, and the environment, generally from alternative media sources including journals, newsletters, weeklies, zines, music, and ...

'' magazine named Ewald as one of the "25 Visionaries Who Are Changing Your World" for his research on the link between infections and cancers.

Quotes

* "Like many great ideas in biology, the idea implicating infectious causation in chronic diseases, though simple, has far-reaching implications. It is so simple and so significant, that one would think it would have been recognized by many and would be the starting point for any discussion on the causes of disease. Not yet." — Paul W. Ewald. * "If I were going to put my money on it, I would bet that by 2050—hopefully earlier—we’ll have found that more than 80 percent of all human cancer is caused by infection." — Paul W. Ewald. * Of Ewald's theory: "It opens our eyes to many quite weird possibilities about disease that most medical scientists, tending to be unaware of current evolutionary thought, don't think of." — evolutionary biologist William D. Hamilton.

Publications

Books

* '' Evolution of Infectious Disease'' (1994)
''Plague Time: The New Germ Theory of Disease''
(2002)

Articles

"Transmission modes and the evolution of virulence"
(1991) * "The Evolution of Virulence: A Unifying Link between Parasitology and Ecology" (1995)
"Guarding Against the MostDangerous Emerging Pathogens: Insights from Evolutionary Biology"
(1996) * "Vaccines as evolutionary tools: The virulence-antigen strategy" (1996) in ''Concepts in Vaccine Development'' * "Alternative Transmission Modes and the Evolution of Virulence" (2002) in ''Adaptive Dynamics of Infectious Diseases'' * "Virulence Management in Humans" (2002) in ''Adaptive Dynamics of Infectious Diseases''
Other publications by Paul Ewald on PubMed

References

External links

Toward a unified, evolutionary theory of cancer
presentation by Paul Ewald 2016
Interview With Evolutionary Biologist Paul Ewald
by Amy Proal
The Big Idea That Might Beat Cancer and Cut Health-Care Costs by 80 Percent
by Andrew Grant, Discover Magazine, Sept 2009

by Judith Hooper, The Atlantic Monthly, Feb 1999

Can we domesticate germs? (TED2007)

The Infection Connection
by Harriet Washington, Psychology Today
List of Human Diseases Linked to Infectious Pathogens
{{DEFAULTSORT:Ewald, Paul W 1950s births Living people American evolutionary biologists University of Washington College of Arts and Sciences alumni University of California, Irvine alumni University of Louisville alumni Year of birth missing (living people)