Genetics
Human Variation and Adaptation
Models of human variation
- Typological model
- Problems: criteria for classification?
- Continuity of human variation
- Discordant variation
- Population model
- Problems: lack of reproductive isolation in humans
- Clinal model
- Geographic distribution of trait frequency
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Takes into account the continuous nature of human variation
- Example: ABO blood group polymorphisms
- Reasons for global distribution
- Gene flow
- Founder effects
- Balancing selection
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Sickle cell trait: combining the forces of evolution to explain
distribution
Human Adaptation
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Stress: interferes with normal limits of the operation of an
organism
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Homeostasis: maintenance of the normal limits of body functioning
- Types of adaptation
- Cultural
- Physiological
- Acclimatization
- Adaptation
- Bioplasticity
- Example: Skin color
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Distribution in indigenous populations follows exposure to
UV radiation
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Adaptation to many factors for both dark and light skin
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Continuity in distribution leaves no room for typology
- Genetic
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Example of Bajau fisherman –complex interaction between
three types of adaptation
Climate Adaptation
- Lewis’ “Hunting phenomenon”
- Bergmann’s rule –warm blooded species
- Body size larger in colder climates
- linear shapes in warmer climates
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Size and shape variation explained by surface area/volume ratios
- Allen’s rule –warm blooded species again
- Colder climates = shorter appendages
- Warmer climates = longer appendages
- Cranial shape –cephalic index
- Nasal shape –nasal index
High Altitude Adaptations
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Varied stressors at altitude: low oxygen, cold, low air pressure;
aridity; high UV exposure, etc.
- Hypoxia –short vs. long term responses
- Developmental responses to hypoxia are numerous
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Responses to high altitude differ among indigenous populations
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Less than 1% of the world’s population lives at greater than 8,ooo
feet
- Altitude stressors
- Oxygen
- Cold
- Air
- pressure
- Food deficiencies
- Dry
- High UV exposure
- Quechua: Increased RBC counts, chest circumference
- Ethiopian highlands: increased hemoglobin levels
- Tibet: increase in of CO2production
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Nutritional adaptation
- Basal metabolic requirement (BMR)
- Total day energy expenditure (TDEE)
- Consequences for undernurtirion
- Delayed development
- Smaller overall
- Susceptibility to infection
- Early death
- Consequences for overnurtirion
- Obesity
- Type II Diabetes
- Osteoarthritis
- Cardiovascular disease
- Hypertension
- Stroke
- Thrifty gene hypothesis
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Differences in the composition of traditional and contemporary
meat products
- Micronutrient deficiencies
- Micronutrient deficiencies
- Relationship between undernutritionand height
Work adaptation
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Bone structure is plastic and influenced by genes, nutrition, and
mechanical forces
- Wolff’s law: bone grows in response to mechanical stress
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Therefore, bone can react to lack of or increases in activity
- Link between excessive workloads and fertility
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