BIO220H1 Lecture Notes - Lecture 19: Evolutionary Medicine, Morning Sickness, Sickle-Cell Disease
Evolution and the Origins of Disease
• body is designed very perfectly but at the same time it has incongruities (e.g. aging and
dying, susceptibility to pathogens). incongruities don't make sense except in the light of
evolution.
• The study of medical problems in an evolutionary context has been termed Darwinian
medicine.
• Darwinian medicine asks why the body is designed in a way that makes us all vulnerable to
problems like cancer, atherosclerosis, depression and choking, thus offering a broader con-
text in which to conduct research.
• evolutionary explanations for the body’s flaws:
• First, some discomforting conditions, such as pain, fever, cough, vomiting and
anxiety, are actually neither diseases nor design defects but rather are evolved
defenses.
• Second, conflicts with other organisms—E. coli or crocodiles, for instance are a fact
of life.
• Third, some circumstances, such as the ready availability of dietary fats, are so recent
that natural selection has not yet had a chance to deal with them.
• Fourth, the body may fall victim to trade- offs between a trait’s benefits and its
costs. e.g. sickle cell gene —> also protects against malaria.
• Finally, the process of natural selection is constrained in ways that leave us with
suboptimal design features, as in the case of the mammalian eye.
1) Evolved Defences
•coughing —> to clear foreign matter from their lung
• feeling pain
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** Cough or pain is usually interpreted as disease or trauma but is actually part of the
solution rather than the problem. These defensive capabilities, shaped by natural
selection, are kept in reserve until needed.
•Fever —> regulated rise in the set point of the body’s thermostat —> facilitates the
destruction of pathogens (also seen in lizards and rats!)
•Reduced iron level —> protective response —> during infection, iron is sequestered
in the liver, which prevents invading bacteria from getting adequate supplies of this
vital element.
•Morning sickness (nausea) —> (thought to be unfortunate side effect of
pregnancy) —> BUT nausea coincides with the period of rapid tissue
differentiation of the fetus, when development is most vulnerable to interference by
toxins. nausea of pregnancy is an adaptation whereby the mother protects the fetus
from exposure to toxins. women with more nausea were less likely to suffer
miscarriages.
•anxiety —> defense in dangerous situations by promoting escape and avoidance
(benefits of fear in seen in guppies)
• vomiting —> to remove toxin is stomach
these are all defences but seem counter intuitive to us so we take drugs to stop them —>
e.g. diarrhea caused by Shigella infection and found that people who took antidiarrhea
drugs stayed sick longer and were more likely to have complications than those who
took a placebo.
e.g. taking iron supplements can severely harm those who are infected and mal-
nourished.
r.g. antinausea drug was recently blamed for birth defects —> by interfering with the
mother’s defensive nausea.
2) Conflicts with Other Organisms
Natural selection is unable to provide perfect protection against all pathogens because they
tend to evolve much faster than humans do
• Antibiotic resistance is a classic demonstration of natural selection (e.g. TB)
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BIO220H1 Full Course Notes
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Document Summary
First, some discomforting conditions, such as pain, fever, cough, vomiting and anxiety, are actually neither diseases nor design defects but rather are evolved defenses. Fourth, the body may fall victim to trade- offs between a trait"s bene ts and its costs. e. g. sickle cell gene > also protects against malaria. Finally, the process of natural selection is constrained in ways that leave us with suboptimal design features, as in the case of the mammalian eye: evolved defences coughing > to clear foreign matter from their lung feeling pain. ** cough or pain is usually interpreted as disease or trauma but is actually part of the solution rather than the problem. These defensive capabilities, shaped by natural selection, are kept in reserve until needed. Antioxidants have antiaging effects, and plasma levels of uric acid in different species of primates are closely correlated with average adult life span.
