Modern Humans: Biological Variation Flashcards
Paradox of Human Variation
A. Homo-sapiens are a young species with an existence of about 200k years.
I. Less genetic variation than other primates
II. Lots of phenotypic diversity (observable characteristics) , some important genetic diversity
Biology’s Definition of Race
- Populations (not subspecies) that are genetically or physiologically distinct
* Applied to many different species; no human populations meet this definition
Def. Genetic Variation
The difference in DNA sequences between individuals within a population.
Examples of Genetic Variation
A. Immune System:
1. ABO Blood type- highly canalized ( reduction of variation), varies geographically and is linked to exposure to different diseases
B. Lactose Intolerance:
1. Cultural adaptations to consuming lactose
2. Genetic adaptations to consuming lactose: the body produces lactase (enzyme that breaks down lactose) for an individual’s entire life
3. Role of Culture: lifelong lactase is only an adaptation if your groups regularly consumes milk and other dairy
Linnaeus & Scientific Racism
- Conflates physical features & moral character
“American Indians”- for example, arme described as not only possessing reddish skin, but are also choleric, paint themselves with fine red lines and are regulated by custom.
“Africans”- are described as having black skin, silky hair and flat noses and are phlegmatic, relaxed, indolent, negligent, anoint themselves with grease and governed by caprice.
“Europeans”- are white, sanguine, muscular, gentle, acute, inventive, have long flowing hair, blue eyes, are covered by close vestments and govern by law.”
Social Darwinism
Darwinism in Human Fitness:
Selective Pressures
1. Diet & Nutrition
2. Disease Exposure
Fitness: The ability to survive and reproduce
Social Darwinism
Fitness Distorted:
Selective Pressure
1. Social Stigmas and expectations
2. Power and hierarchy
3. Structural Violence
Fitness: the RIGHT to survive and reproduce
Eugenetics Movement
Eugenetics: Improvement of Humanity
- Genetic purity & alleviation of suffering
- Removal of “degenerate” traits
- Society becomes healthier, more intelligent
Eugenetics: Ways to maintain purity
- Restricted marriage
- controlled immigration
- segregation
- forced sterilization
-extermination - Nazi rhetoric
Polygenic vs. Monogenism
Polygenism is the theory that the human races have seperate origins
Monogenism theorizes that the species came from only one ancestral line or origins
What is race pertaining to Biological race?
Race is a genetically distinct population
Genetic traits…
Are non noncordant (ex. Not all pale-skinned people all have blond hair and blue eyes)
Apportioning Racial Diversity
*Majority of allelic variation (# of allele forms on a chromosome) is between individuals, not between large populations
- 6% of humans genetic diversity corresponds to culturally-assigned racial category
Commonly Used Racial Criteria
Skin Color: subjective, based on looks and not function
Facial Features
Body size/ physique
Biologically Meaningful… as an adaptation; not necessarily reflective of descent
What is the Epidermis
Is the outer layer of the skin
- contains thin layers of keratinocyted (basal cells) that divide and then migrate to the skin’s surface
- lowest level of epidermis contains melanocytes (melanin-forming cell)
What is the dermis?
Is the inner layer
- blood cells, nerves, hair follicles, glands
Function of Melanocytes
Produces melanin granules and finger-like dendrties transport the melanin throughout the epidermis
Melanin= Pigmentation
- Most people have the same # of melanocytes
- the amount , the size, the rate, and the location of melanin produced influences the degree of pigmentation
- Skin pigmentation= measure of photoreflectivity
Golfer’s Rule
*Darkness of skin is correlated with humid environments which tend to occur in equatorial zones.
-Mammals or birds in the tropics appear to have black coloration
- Mammals or birds in the arctic have white coloration
- Human populations follow this general pattern
UV Radiation effects of Lightly Pigmented People
Lightly pigmented people exposed to strong sunlight have clinically low levels of the essential B vitamin folate in their blood
Folate deficiency related to increased neural tube defects
- UVB radiation breaks up folate molecules
Not Enough UVR + Too Much Melanin
Lack of vitamin D= bones fail to mineralize properly during development
-Osteomalacia: softening of bones
Selective pressure:
- increases infant mortality
Cultural Cofounders
- Clothing in areas of high UV radiation
- Adaptive for insulating against heat stress
- Problematic for UV absorption
- Behavior that limits UV exposure in those with dark pigmentation
Body Size: Bergman’s Rule
As body size increases:
> there is an increase in the amount of metabolizing tissue, therefore internal heat gain is greater
> there is an overall decrease in the surface area to mas ratio, meaning that heat loss is reduced
*Body size tends to be negatively correlated with temperature
Body Size: Allen’s Rule
- The length of body extremeties is positively correlated with temperature
> Long, slender arms and legs is increased by assuming a more linear form
evaporation loss is directly proportional to the amount of exposed surfaced area
Who is Frans Boas?
Founding Father of American Anthropology
> emphasized connections between human’s biology, culture, language, both past and present
What is The Immigrant Study?
- tested the influence of environment on head shape & body size
-17,821 people - found that US-born children were taller with bigger heads
*pointed to the plasticity of bodily form & the importance of culture in shaping it
- Nutrition
- Sanitation
- Relative Safety
How do we interpret human variation?
> Genetics
Environment
Culture
Race as Identity and Lived Experience
-Early Socialization= early exposure to systems of racism & discrimination during brain development
Historic “Doll Test”
*The results from the doll test showed that the majority of black children preferred the white dolls over the black dolls
> Segregation gave African American children a sense of inferiority
