Ch 4 Human Variation and Adaptation Flashcards Preview

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Flashcards in Ch 4 Human Variation and Adaptation Deck (37)
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Johann Friedrich Blumenbach

- Classified humans into 5 races
- “White, yellow, red, black, brown”


The Concept of Race

- In biology a category with subspecies
- Based on distinctive physiological, morphological, and ecological features
- Easily observed differences among humans from major geographic areas


The Concept of Race: What's wrong with that? (2)

- Look at its enormous sociocultural significance
- Look at why it doesn’t hold up biologically


The Concept of Race: Where do we draw the Line?

- Easy to see extremes – what about all the variation in the middle?
- “Falls apart” when we start to draw lines
- Occurs on a continuous spectrum, not ‘present vs. absent’ but ‘more vs. less’
- Difficult whether we divide people into 3, 5 or even 30 ‘micro’-races


The Concept of Race: Who gets to draw the Line?

- Many examples of dominate group using race for oppression, subjugation, sterilization and genocide
Ex. eugenics movement


Human Polymorphisms

- Loci with more than one allele (ex. ABO blood type)
- Examining single traits can help when looking at natural section or gene flow, but are limited
- Studying several traits simultaneously helps us understand relationships between populations
- Examining these traits can tell anthropologists lots about our history


Alberta Sexual Sterilization

- Drafted under the guises of protecting the gene pool
- Sterilizing mentally unwell people to prevent the passing of mental illness
- Criminal behaviours, mental illness, prostitution etc. all deemed mental illnesses
- There was a fear that the gene pool would be weakened if these "not normal" people were allowed to "breed"
- Lied to about the fact they would be 'sterilized' during another operation (ex. Dental work)
- Women, men, children


Considerations about Race:
Human Populations are Heterogeneous

- We recognize there is variation between different human populations
- Discrediting the notion of race does NOT mean scientists are suggesting there are no phenotypic or genetic differences


Considerations about Race:
Polygenic traits are difficult to measure accurately

- Skin pigmentation is difficult to measure accurately
- What/ how are you counting?
- Hard to determine how much was genetic versus how much was environmental


Considerations about Race:
Discrete Boundaries

- A continuously varying trait has no inherently meaningful boundaries!
- Boundaries are always arbitrary and thus subject to bias


Considerations about Race:
Traits are not linked

- Features ascribed to different races do not co- occur together – they are not phenotypic or genotypic clusters
- Ex skin color, hair colour & texture, facial physiognomy all occur on different chromosomes through different alleles, therefore they do not co vary


Considerations about Race:
Specific # of traits cannot define a race

- How many features are necessary to assign race?
- It is arbitrary; there is no agreement on how many differences it takes
- No single feature can clearly assign race
- No ‘race’ has exclusive possession of any particular variant of a gene or genes


Considerations about Race:
Genetic Diversity

- How much genetic diversity actually matters?
- Lewontin (1972) study – over 85% of genetic diversity occurs among individuals within populations


Considerations about Race:
Gene flow

- Populations are genetically “open,” meaning that genes flow between them
- No fixed racial groups can ever exist
- Humans have always inbred



- A gradient over which the frequency of expression of a trait changes
- Create a map of changes in trait expression based on measured frequencies
- “There are no races, there are only clines.”
- Ex. sickle-cell anemia cline


Solar Radiation:
Darker Skin

- In areas closer to the tropics, natural selection favoured deeply pigmented skin
- Early Hominins lived in tropics, with minimal shade, and didn’t wear clothing
- Environment favoured high production levels of melanin (to protect from UV rays)


Solar Radiation:
Lighter Skin

- As Hominins migrated they entered colder, cloudy environments
- The dark pigment blocking UV rays also blocked vitamin D, so natural selection began favouring lighter pigmented skin


Lactose Tolerance

Recent human evolution
- The ability to digest lactose depends on the enzyme lactase
- All children have this ability but in many it is lost by adolescence
• Breastfed when they were younger, stopped as they grew up


Lactose Tolerance:
African vs. European

• In European cultures it was common to drink milk past childhood, so most adults kept this enzyme
• In African cultures they did not, so they tend to be less tolerant to lactose


Thermal Environment

- Mammals and birds have physiological mechanisms to maintain constant body temp
- Human habitats range from 120° F (49° C) to -60° F (-51° C).



• Physiological responses to changes in the environment that occur during an individual’s lifetime
• Responses may be temporary or permanent
• Subject to evolutionary factors such as selection


Human's Response to Heat

- Long term adaptations to heat evolved out ancestors
- Sweat Glands and Loss of Body Hair
• Distributed throughout body, making cooling easier
• Loss of hair helped


Human's Response to heat:

• Capillaries near the skin’s surface widen to increase blood flow
• Allows the skin to radiate heat


Bergmann's Rule

"Body size changes in different climates"
In cold, body size is large
In warm, body size is small
- Larger bodies have smaller surface area to volume ratios


Allen's Rule

In cold, body is more rounded and compact

In warm, body size is more linear
- Round forms have smaller surface area to volume ratios


Human's Response to Cold:
Short Term

- Increase heat production
- Enhance heat retention
- Ex. Shivering
• Short term response to generate heat, but energetically expensive


Human's Response to Cold:
Long Term

- Seen mainly in groups acclimated to living in cold environment
- Maintain high metabolic rate


Human's Response to Cold:

• Narrowing of blood vessels to reduce blood flow
• Short term response to retain heat and conserve energy
• *Concern is frostbite


High Altitude:
Factors (5)

1. Hypoxia (reduced available oxygen)
2. Intense solar radiation
3. Cold
4. Low humidity
5. Wind


High Altitude:
Growth& development

• Larger heart size
• Greater lung capacity
• More efficient diffusion of oxygen to body tissues