http://artemis.austincollege.edu/acad/hwcis1/2005/evolutionary%20medicine.2005.pdf
HWC 44 – UNIT 3 – THE DARWINIAN REVOLUTION –
Outline for LECTURE
10
EVOLUTIONARY MEDICINE,
INTELLIGENT DESIGN? BENEVOLENT DESIGN?
Evolutionary Medicine/Darwinian Medicine
(the hunt for evolutionary explanations of vulnerabilities to disease)
I. Evolution of pathogen resistance (to both drugs and immune system responses)
A. Pathogens (= disease causing organisms) – bacteria and viruses (e.g., flu) (50-100 million
people killed by flu epidemic of 1918; origins of pandemic flu strains-molecular evidence of
mixing of pig, bird and human strains; HIV virus; tuberculosis (multi-drug resistant strains—
Russian prisons; poverty; implications); other implications: routine use of antibiotics on
animals (bacteria exchange genetic material)
B. Selection pressures on pathogen – evolution of resistance to both drugs and human immune
system responses is natural selection in action
C. Symptoms – e.g., runny nose, diarrhea – who benefits? Host or pathogen? Not immediately obvious
D. Importance of evolution in tracing origin of diseases – evolutionary trees
II. Side effects of imperfect evolved responses/evolutionary compromises:
A. Heterozygote advantage/balanced disadvantage (tradeoffs): sickle-cell anemia (malaria), Tay-
Sachs disease (tuberculosis), cystic fibrosis (cholera) – evolution works with what is available –
solutions to all problems not genetically available at any given point in time – many imperfect
adaptations
B. Changed conditions/different environment/anachronisms (result in imperfections at present
time)
1) Under what conditions did we evolve?
2) Now living in novel environments – rate of cultural change has outpaced ability of natural
selection to keep up; therefore, we have some anachronisms
3) Myopia (shape of growing eye molded by visual experience); breast cancer rates (1 in 8
women here vs. 1/12
th
the rate among West African women: possibly partly due to toxins,
but women’s bodies not evolved to tolerate continual menstrual cycling, hormone flux;
carbohydrate metabolism (Sweet Death); high salt intake (results in high blood pressure);
arteriosclerosis (rare among hunter-gathers); why do we make poor diet choices? (our brains
evolved in situations where fat, salt, & sugar were rare and good for us in limited quantities);
psychoactive drugs (mimic/modify natural brain chemistry); hygiene hypothesis & allergies
C. Various imperfect adaptations in the human body – unfortunate legacies of our evolutionary past
Examples: female knee, inguinal hernias, prostate gland and urethra, eye (blind spot,
detached retinas), low back problems, weak bladder ligaments, problems at birth; shared
food and air passages – If Humans Were Built to Last – evolutionary compromises,
historical constraints
D. Are all of these imperfections the result of “intelligent” design; if so is the designer benevolent?
Suffering and death (including of babies) as the result of imperfect “designs”?
III. Adaptive evolution as key to understanding certain phenomena
A. Examples: Defenses (fever, vomiting, diarrhea, morning sickness–protects fetus, reduced levels of iron
in the blood–deprives parasites, pain); behaviors–jealousy, biophilia/biophobia (e.g., real vs.
perceived dangers, snakes; blood pressure & fish tanks)
B. Precautionary principal in terms of defense – e.g., vomiting; nature’s “smoke alarms”, smoke-detector
principle, causes a lot of suffering, but reduced risk of death
IV. Summary – we have many extraordinary adaptations, but also many imperfections – we’ve been cobbled
together (our bodies are a Rube Goldberg device (= a complex apparatus that performs a very simple task
in a very indirect and convoluted way); “Nothing in biology makes sense except in the light of evolution”;
proximate vs. ultimate (evolutionary) explanations.
In general, Darwinian medicine tells us that the organs and systems that make up our bodies result not
from the pursuit of perfection, or from perfect “design”, but from millions of years of evolutionary
compromises designed to get the greatest reproductive benefit at the lowest cost; there are many
implications for modern medicine