Proximate and Ultimate Questions

Topics: Evolution, Infectious disease, Charles Darwin Pages: 25 (5037 words) Published: May 18, 2012
Evolutionary (Darwinian) Medicine
“Nothing in biology makes sense except in the light of evolution” –Theodosius Dobzhansky

Proximate vs. Ultimate Questions
Biological causation: proximate vs. ultimate explanations
Physiology, genetics, biochemistry, etc. generally concentrate on * proximate causation
“What” & “How” questions
Ultimate causation: How evolutionary processes (natural selection; adaptation) and evolutionary history shape traits “Why” questions
Traits have both types of causes—a complete biological explanation requires analysis of both Examples: Childbirth, obesity, high blood pressure and asthma/allergy

The Big Picture: Hominid Origins
What are the key features that define us as humans & when did they arise? Why did these features evolve?

How does an understanding of adaptation in earlier hominids help us understand contemporary human health issues? Evolutionary history important for understanding modern human * condition
Two examples:
1) Bipedalism & low back pain
Why did it evolve? An extremely efficient way to travel long distances (also frees the hands for carrying) But predisposed to back pains
Viewed as a product of design constraints & trade-offs
2) Bipedalism and brain size on infant growth and development (the “obstetric dilemma”) Requires a shift in life history pattern
Early birth (risk for SIDS)
Requires high quality diets and ability to store large amounts of fat Can identify times of increased risk for nutritional problems Explains human propensity for consuming energy dense foods

A Key Concept - Novel Environments
Contemporary cosmopolitan, urban environments as novel
Widespread availability of energy dense foods (especially fats & refined carbohydrates) Certain highly energy dense foods (especially liquids) “override” the system Our metabolism is evolved to be thrifty, making it difficult to diet to lose fat Links between chronic psychological stress & fat amount/pattern

Some Surprising Answers
New perspective on asthma, allergy, and autoimmune diseases
Allergy increasing in the US & developed nations
50 million in US with some type of allergy
Protective effect of microbial exposures
Decreased exposure to helminths (parasitic worms), viruses, and bacteria leads to increased risk of allergy, autoimmune disease, type I diabetes, and other diseases Immune system tuned by environmental exposure

New treatments developed that use helminth (e.g., whipworm) introduction *
* A New Perspective on Aging
Why do we experience more diseases with age?
Many physiological processes decline with age but not in all * Circumstances
How much is programmed vs. byproduct of our lives?

Are Humans Still Evolving?
Until only a few years ago most scientists would have said “No” Food production & population expansion
Culture: Modern medicine
Evidence for evolution since beginning of food production
Including selection (sickle cell allele, lactose tolerance, etc.) Evidence for ongoing evolution
Including selection (malaria resistance, skin color, skeletal development)

Does medicine without evolution make sense?
Evolutionary perspective complements existing biomedical frameworks—It does not replace it Provides valuable information on:
Why diseases exist at all & our greatest disease vulnerabilities Why disease is unequally distributed between individuals & groups Not just an academic exercise but can influence:
How diseases are treated clinically
Public health practices & personal health decisions

The study of humankind using an integrative approach
Culture & society (human variation & universals)
Culture and society in the past (historic & prehistoric) Culture and society in the past (historic & prehistoric) Biological anthropology is the study of human biology and behavior within the framework of evolution, with an emphasis on the interaction between biology and culture...
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