INTRODUCTION Evolution by natural selection has been biology's organizing principle for more than a century, but only in the last few decades has it been applied to the social sciences and medicine. Its application to medicine, known as evolutionary or Darwinian medicine, uses an evolutionary perspective to understand why the body is not better designed and why, therefore, diseases exist at all.1,2,3 This article outlines some basic principles of Darwinian medicine, summarizes the usefulness of evolutionary principles for medicine, and provides some examples from key literature sources. For example, traditional clinical medicine looks at the problem of obesity in terms of individual differences that explain why one person becomes obese and another does not. These factors may be due to genes, early environment, or current lifestyle. Now that one half of Americans are overweight, however, it is time to answer the evolutionary question: why are our bodies designed so that most of us eat too much and exercise too little? Go to: EVOLUTIONARY EXPLANATIONS FOR OBESITY An initial answer is simple. In the environment in which we evolved, natural selection shaped appetite regulation mechanisms to ensure that we survived periods of famine. In those ancient times, eating required walking for hours each day to get food, a caloric cost that made it impossible for most people to accumulate much surplus as fat.4 Exposure to intermittent periods of food shortage sets off a system that prepares for a coming famine by increasing appetite and basal weight above the starting point. Dieting activates the same system, so weight can rebound to above what it was when the diet began. When young people try to lose weight by using willpower to drastically limit their food intake, their regulation mechanisms react with a response that is adaptive: they often gorge themselves. These episodes of uncontrolled eating can make the dieter even more fearful of becoming obese, so still further efforts of will arouse the mechanism more strongly, setting in cycle the positive feedback spiral we see in anorexia and bulimia. As for our food preferences, one would think we would be designed to eat what is good for us. The system would work fine if we lived on the African savanna. In the natural environment, fat, salt, and sugar are in such short supply that when they are encountered, the useful response is to consume them. Fat provides twice as many calories per gram as carbohydrates. Sugar is often associated with ripe fruits, and seeking it out was usually beneficial. Now that we can choose our foods, we prefer what was in short supply on the African savanna. We also choose our levels of exercise to minimize caloric expenditure—a wise strategy in the Paleolithic era when wasting calories could bring death. This tendency to be sedentary, in combination with our preferences for large amounts of high-calorie, high-fat food, has resulted in an epidemic of atherosclerotic disease. N.

1. INTRODUCTION
Evolution by natural selection has been biology's organizing
principle for more than a century, but only in the last few
decades has it been applied to the social sciences and medicine.
Its application to medicine, known as evolutionary or Darwinian
medicine, uses an evolutionary perspective to understand why
the body is not better designed and why, therefore, diseases
exist at all.1,2,3 This article outlines some basic principles of
Darwinian medicine, summarizes the usefulness of evolutionary
principles for medicine, and provides some examples from key
literature sources.
For example, traditional clinical medicine looks at the problem
of obesity in terms of individual differences that explain why
one person becomes obese and another does not. These factors
may be due to genes, early environment, or current lifestyle.
Now that one half of Americans are overweight, however, it is
time to answer the evolutionary question: why are our bodies
designed so that most of us eat too much and exercise too little?
Go to:
EVOLUTIONARY EXPLANATIONS FOR OBESITY
An initial answer is simple. In the environment in which we
evolved, natural selection shaped appetite regulation
mechanisms to ensure that we survived periods of famine. In
those ancient times, eating required walking for hours each day
to get food, a caloric cost that made it impossible for most
people to accumulate much surplus as fat.4 Exposure to
intermittent periods of food shortage sets off a system that
prepares for a coming famine by increasing appetite and basal
weight above the starting point. Dieting activates the same
system, so weight can rebound to above what it was when the
diet began. When young people try to lose weight by using

2. willpower to drastically limit their food intake, their regulation
mechanisms react with a response that is adaptive: they often
gorge themselves. These episodes of uncontrolled eating can
make the dieter even more fearful of becoming obese, so still
further efforts of will arouse the mechanism more strongly,
setting in cycle the positive feedback spiral we see in anorexia
and bulimia.
As for our food preferences, one would think we would be
designed to eat what is good for us. The system would work fine
if we lived on the African savanna. In the natural environment,
fat, salt, and sugar are in such short supply that when they are
encountered, the useful response is to consume them. Fat
provides twice as many calories per gram as carbohydrates.
Sugar is often associated with ripe fruits, and seeking it out was
usually beneficial. Now that we can choose our foods, we prefer
what was in short supply on the African savanna.
We also choose our levels of exercise to minimize caloric
expenditure—a wise strategy in the Paleolithic era when
wasting calories could bring death. This tendency to be
sedentary, in combination with our preferences for large
amounts of high-calorie, high-fat food, has resulted in an
epidemic of atherosclerotic disease. Natural selection will
eventually fix such design problems, but it will take hundreds or
thousands of generations to do so.
Go to:
EVOLUTION AND ANXIETY DISORDERS
Anxiety disorders offer another example of Darwinian medicine
in action.5 We know anxiety can be useful, but why do so many
people experience so much of it, so often, when it seems worse
than useless?
In ancient times, anxiety was necessary for humans to flee from
a predator. This “fight and flight” mechanism is built into our

3. nervous systems. It is triggered at the wrong time in people with
panic disorder. If a panther were approaching, however, it
would be valuable. Agoraphobia, the fear of open spaces and the
tendency to stay close to home or to flee at the least hint of
danger, is considered a phobia in modern societies, but is the
optimal response if predator attacks have been frequent.5
Go to:
SYMPTOMS AS EVOLUTIONARY DEFENSES
An evolutionary approach can fundamentally change how we
think about the body and disease.6 Instead of seeing disease as
a defect in a previously perfect machine, Darwinian medicine
allows us to see the body as a product of natural selection, full
of trade-offs and vulnerabilities that all too often lead to
disease. Physicians are not mechanics repairing broken parts;
they are guides who understand the trade-offs that give rise to
disease and come up with strategies that will oppose the effects
of other organisms, compensate for what the body cannot repair,
and relieve suffering when possible.
For example, pain, nausea, cough, fever, vomiting, diarrhea,
fatigue, and anxiety are common medical problems. Much of
medical practice focuses on relieving suffering by prescribing
medications that block these responses. A different view is that
these responses are not problems themselves but represent the
body's attempt to remedy a problem. If defenses are so useful,
and natural selection is potent, then prescribing medicines may
be unsafe. If fever, cough, and diarrhea are useful defenses,
blocking them might make people sicker. Treating Shigella-
induced diarrhea, for example, substantially increases
complications.7 The excessive suppression of cough can cause
death. Extreme circumstances require a balanced approach,
however; for example, blocking fever can prevent febrile
seizures, and stopping vomiting can prevent dehydration.
Why has natural selection shaped the body so these defenses are

4. expressed so readily and intensely? The answer is the same as
the explanation for why we tolerate smoke detectors that sound
a false alarm every time the toast burns. You could design a
detector that went off only when there was extensive smoke, but
the disadvantage would be the absence of the alarm in response
to some fires. Defenses such as pain and fever are inexpensive
compared with the dangers they avert, so natural selection has
shaped regulation mechanisms that express them whenever they
might be useful. As a result, it is usually possible to block them
safely.8 As for that most hackneyed bit of medical advice, “take
aspirin and drink plenty of fluids,” perhaps studies will soon be
conducted to determine if this speeds or slows recovery from
everyday infections.
Go to:
CLINICAL APPLICATIONS OF DARWINIAN MEDICINE
Understanding common illnesses
Most medical research asks why one person gets a disease and
another does not. Darwinian medicine suggests asking an
additional and different line of questioning: why are we all
vulnerable to certain diseases?6,9 Why are we all likely to get
hemorrhoids, impacted wisdom teeth, and pneumonia? Why will
so many of us experience myocardial infarction, cancer, or
rheumatoid arthritis?
Most people think that the answer is simply that natural
selection cannot make the body any better than it has. After all,
it is a random process with no direction or coordination. In fact,
the body is not better designed for specific evolutionary
reasons.
One important reason is that natural selection does not shape
organisms for health or longevity but for maximizing
reproduction, even at the expense of a shortened life span.
When there is a conflict—for instance, when a gene improves

5. bone healing in youth but also causes arterial calcification—that
gene will be selected for even though it leads to fatal outcomes
in later life. Where there is a conflict between reproductive
success and health, reproduction always wins out.10
Answering questions about etiology
Another way in which evolutionary biology is useful in
medicine is to answer classic questions about the etiology of
disease. For instance, evolutionary medicine can provide
specific approaches to the problem of antibiotic resistance. The
story of pathogen virulence provides the best example. It seems
that it would not be in their interests for pathogens to kill the
host that supports them. Given sufficient time, virulent
pathogens should gradually evolve into a benign mutualism with
their hosts. The steady decrease in the virulence of syphilis over
the past 5 centuries has often been interpreted in this way,
probably correctly. Pathogens that cause severe and often fatal
disease, such as cholera, are thought to be still in the process of
adapting to their host.
This notion is incorrect, however. In work summarized by
Ewald, it became clear that natural selection shapes whatever
level of virulence maximizes the replication of bacteria and
viruses.11,12 Often, as with rhinovirus, the pathogen spreads
more rapidly if the host is up and around. Other pathogens,
however, such as Plasmodium species are spread by vectors.
Mosquitoes are more effective vectors when the host is
prostrate. Genetic variants that replicate more quickly are
selected for and increase in prevalence.
This fact has immediate practical implications for infection
control. The hands of medical staff are a vector, so it is not
surprising that nosocomial Escherichia coli strains tend to
become increasingly virulent with the duration of circulation in
a medical setting. Furthermore, these organisms are exposed to

6. antibiotics, so they are likely to become resistant to treatment.
A neonatal nursery is well designed for breeding “superbugs.”
The difficulty of exterminating these bugs may warrant cutting
off their evolutionary pathway occasionally by moving nurseries
at intervals to a completely different sterile room with fresh
supplies and no transfer of infants from the previous nursery.
The prospect of interrupting the further evolution of nosocomial
pathogens might justify the considerable expense.
Identifying improvements for public health
Where water supplies are contaminated by sewage, selection
acts to increase virulence. Public sanitation changes the
selection forces, giving the advantage to less virulent
organisms. Where new sources of clean well water have been
provided, especially in India, virulent pathogens such as
Shigella dysenteriae and classic Vibrio cholerae have been
replaced by less virulent Shigella flexneri and the El Tor
subtype of V. cholerae.13
Go to:
CONCLUSION
Everyone uses metaphors to understand the world. The
dominant metaphor for the body has been a machine. Disease
has been viewed as a defect arising in an otherwise perfect
device. An evolutionary view offers a richer and more nuanced
view of the body as a product of natural selection: extraordinary
in many ways, but also flawed in many ways, for good
evolutionary reasons. Furthermore, it reveals that the body has
no master plan and there is no such thing as “the” human
genome. Humans have genes that make phenotypes that
effectively make new copies of themselves. We care less about
the fate of our genes, however, and more about the health and
welfare of individuals.
Darwinian medicine will most powerfully advance our goal of

7. helping individuals by inspiring research that yields solid new
findings to guide health care practice. Even at this early stage,
however, Darwinian medicine can help clinicians answer old
questions, pose new questions, and provide a more natural view
of disease.
Notes
Competing interests: None declared
Go to:
References
1. Williams GW, Nesse RM. The dawn of Darwinian medicine.
Q Rev Biol 1991;66: 1-22. [PubMed]
2. Nesse RM, Williams GC. Why We Get Sick: The New
Science of Darwinian Medicine. New York, NY: Vintage; 1994.
3. Stearns S, ed. Evolution in Health and Disease. Oxford:
Oxford University Press; 1998.
4. Eaton SB, Konner M. Paleolithic nutrition: a consideration of
its nature and current implications. N Eng J Med 1985;312: 283-
289. [PubMed]
5. Marks IM, Nesse RM. Fear and fitness: an evolutionary
analysis of anxiety disorders. Ethol Sociobiol 1994;15: 247-261.
6. Nesse RM, Williams GC. Research designs that address
evolutionary questions about medical disorders. In: Stearns SC,
ed. Evolution in Health and Disease. New York, NY: Oxford
University Press; 1999: 16-26.
7. DuPont HL, Hornick RB. Adverse effect of lomotil therapy in
shigellosis. JAMA 1973;226: 1525-1528. [PubMed]
8. Nesse R. The smoke detector principle: natural selection and
the regulation of defenses. In: Damasio AR, Harrington A,
Kagan J, McEwen B, Moss H, Shaikh R, eds. Unity of
Knowledge: The Convergence of Natural and Human Science.
New York, NY: New York Academy of Sciences; in press.
9. Trevathan WR, McKenna JJ, Smith EO, eds. Evolutionary
Medicine. New York, NY: Oxford University Press; 1999.
10. Williams GC. Pleiotropy, natural selection, and the

8. evolution of senescence. Evolution 1957;11: 398-411.
11. Ewald P. Evolution of Infectious Disease. New York, NY:
Oxford University Press; 1994.
12. Ewald PW. The evolution of virulence: a unifying link
between ecology and parasitology. J Parasitol 1995;81: 659-
669. [PubMed]
13. Ewald PW. Evolutionary biology and the treatment of signs
and symptoms of infectious disease. J Theor Biol 1980;86: 169-
176. [PubMed]
Fill in the blanks. (5 points each)
PART I
A. Asthenosphere D. Ocean ridge system
B. Lithosphere E. Alfred
Wegener
C. Pangaea
1. A single supercontinent consisting of all Earth’s landmass
that began to break up about 200 million years ago was called
________________________.
2. In 1915, a German meteorologist and geophysicist named
_________________ wrote The Origin of Continents and
Oceans and set forth a basic outline of the hypothesis called
continental drift.
3. The uppermost mantle, along with the overlying crust,
behaves as a strong, rigid layer known as the
_________________________.

9. 4. Through later technology a much better picture of large
expanses of the seafloor slowly and painstakingly began to
emerge. From this work came the discovery of a global
____________
_____________________that winds through all of the major
oceans in a manner similar to the seams on a baseball.
5. The ____________________ is a subdivision of the mantle
situated below the lithosphere. This zone of weak material
exists below a depth of about 100 kilometers and in some
regions extends as deep as 700 kilometers. The rock within this
zone is easily deformed.
PART II
A. Convergent plate boundaries D.
Paleomagnetism
B. Transform plate boundaries E. Hot spot
volcanism
C. Divergent plate boundaries
6. Rocks that formed thousands or millions of years ago and
contain a “record” of the direction of the magnetic poles at the
time of their formation are said to possess fossil magnetism, or
________________________.
7. _______________________ occur where two plates move
toward each other and the leading edge of one is bent
downward, as it slides beneath the other. This is where crust is
destroyed or recycled.
8. _________________________ occur where two plates move
apart, resulting in upwelling of hot material from the mantle to
create new seafloor.

10. 9. A ______________________ is a concentration of heat in the
mantle capable of producing magma, which in turn extrudes
onto Earth’s surface. The intraplate volcanism that produced the
Hawaiian Islands is one example.
10. ___________________ are where two plates grind past each
other without the production or destruction of lithosphere.
PART III
A. Liquefaction D.
Epicenter
B. Elastic rebound E.
Magnitude
C. Focus
11. The origin of an earthquake occurs at depths between 5 and
700 kilometers, at the _______________.
12. The point at the surface directly above the focus is called
the _____________________.
13. A quantitative measurement , called ________________,
relies on data gleaned from seismic records to estimate the
amount of energy released at an earthquake’s source.
14. ______________________ is the sudden release of stored
strain in rocks that results in movement along a fault. This
actual mechanism of earthquake generation was discovered by
H.F. Reid following the great 1906 earthquake in San Francisco.
15. In areas where unconsolidated materials are saturated with
water, earthquake vibrations can turn stable soil into a mobile
fluid, a phenomenon known as ______________________.

11. PART IV
A. Brittle deformation D. Faults
B. Ductile deformation E. Folds
C. Orogenesis
16. The term for the processes that collectively produce a
mountain belt is _________________.
17. Along convergent plate boundaries, flat-lying sedimentary
and volcanic rocks are often bent into a series of wavelike
undulations called ________________.
18. _______________ are fractures in the crust along which
appreciable displacement had taken place.
19. _____________________ is a type of solid-state flow that
produces a change in the size and shape of an object without
fracturing.
20. Rocks near the surface, where temperatures and confining
pressures are low, tend to behave like a brittle solid and fracture
once their strength is exceeded. This type of deformation is
called
_______________________.
Movie Critique
Due Friday by 11:59pm Points 25 Submitting a file upload

12. Available Jun 21 at 12am - Jul 3 at 11:59pm 13 days
Submit Assignment
Hollywood and History
There are many wonderful films to view that chronicle
historical events. Hollywood has a strong "history" in
producing
them. Recently, there was the film about Harriet Tubman.
This genre of film is issued on a regular basis. Here is an
opportunity to view a film and write a critique.
Please follow the simple guidelines. You may do this
assignment in lieu of the Oral History. Your paper is due July
3.
The paper is an ESSAY. You will provide an introduction, a
body and a conclusion. DO NOT respond in separate
prompts. I want an essay. You will tell a story and you will
use the prompts to explain the movie and your thoughts
about it. You briefly retell the story. You examine its
historical accuracy citing at least one source. Simply state
your
source that you consulted. How would you improve the movie;
this is your conclusion and shall be thorough.

13. I want you to look at films that start with the Conquest and
move through the 1899. No earlier and no sooner. Some
ideas: Conquest of Paradise, Black Robes, Amistad, The New
World, Glory, 12 Years a Slave, Harriet, Birth of a
Nation (2016 version), Amazing Grace, The Patriot, Gettysburg,
Cry No More Forever, Last of the Mohicans ... there is
a long list. If you have a question, just let me know.