Ch 4 Human Variation and Adaptation Flashcards
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
Cline
- 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
European
• In European cultures it was common to drink milk past childhood, so most adults kept this enzyme
African
• 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).
Acclimatizations
- 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:
Vasodilation
- 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:
Vasoconstriction
- Narrowing of blood vessels to reduce blood flow
- Short term response to retain heat and conserve energy
- *Concern is frostbite
High Altitude:
Factors (5)
- Hypoxia (reduced available oxygen)
- Intense solar radiation
- Cold
- Low humidity
- Wind
High Altitude:
Growth& development
- Larger heart size
- Greater lung capacity
- More efficient diffusion of oxygen to body tissues
High Altitude:
The Indigenous Peoples of Tibet
- Lived at ~12,000 ft for many thousands of years
- Burn glucose in a way that permits more efficient use of oxygen
- Alterations in maternal blood flow to placenta
- Strong example of natural selection in humans (happened quickly over 4000 years)
Infectious Disease:
Causes- Biological& sociocultural (6)
- Rural vs. urban
- Agriculture
- Exposure/consumption of domesticated animals
- Socioeconomic status
- Living conditions, sanitation
- Religious/ideological beliefs
HIV/AIDS:
Stats and dates
- First confirmed case in US in 1981
- Present at least as far back as 1959 in West Africa
- 95% of people with HIV are in the developing world
- In 2012 estimated that 28 million people are living with HIV (World Health Organization)
HIV/AIDS:
Origin
- Interspecies transfer infection
- HIV 1 evolved from simian immunodeficiency virus (SIV) found in gorillas, chimpanzees and African monkeys
HIV/AIDS:
Genetics
- Altered receptor site in immune cells prevents HIV from entering
- Mutation found in about 10% of people with European decent
- *** Too recent of a disease for there to be evolutionary changes
- Didn’t make sense that some people had the mutation preventing it
- Would have to have come from some previous disease
- Bubonic plague (Black Death; 14th C)??
- Smallpox (17-18th C)??
Smallpox
- The only disease considered to be eliminated as a result of medical technology
- More common in people with type A or AB blood, than those with type O blood
Why? We aren’t sure
- The immune system of those with type A blood may not see it as a threat
- As a result, their body would not fight as effectively against small pox
Impact of Infectious Disease:
& Antibiotic Resistance
- # 1 cause of death before 20th century
- Since the 1940s, antibiotics have reduced mortality
- Between 1980 and 1992 deaths from infectious disease increased by 58%.
- Could be a result of overuse of antibiotics
- Bacteria and viruses evolve quickly (short lifespans) and become resistant to antibiotics
