ANT 201: Week 3

Human Variation & Adaptation 09/12/23

Evolutionary and non-evolutionary

Today:

• Body size/proportions
• Blood types
• Dental morphology
• Sex

Polymorphisim= variations exist

Phenotype Plasticity= changes to phenotype in response to the environment (stressors)

• Body trying to maintain homeostasis
• No genetic change
• Indiv. Level changes
• Acclimation, developmental, behavioral

Adaptation= increase in frequency of a trait as a result of natural selection

• Genetic (not temporary)
• Population-level

EX:

Altitude

Major stressor: hypoxia [not enough oxygen]

Plastic changes:

• Developmental= slower growth, increased heart and lung capacities
• Acclimatory= increased erythropoiesis/hemoglobin (EPAS!)

- ↑in RBC

• Behavioral/cultural= oxygen tanks

Adaptive Changes

• Increased lung volume among Andean populations (chest shape), increased hemoglobin

—> EPAS1 variant in Tibetan Plateau (keeps hemoglobin concentrations low)

• 87% of the population vs, 9% HAN Chinese

Bergmann’s and Allen’s Rules

• Larger body mass to lower surface area ratio= retains more heat
• Larger surface area = dissipates more heat

Bergmann’s Rule

• Larger objects will lose heat at a slower rate than smaller objects

- large bodies built for cold environments

- smaller bodies are built for hot environments

Allen’s Rule

• Linear objects will have greater surface area than more cubic objects of the same volume
• More surface area = more efficient heat loss

Proportionality longer limbs → more surface area → more heat loss → keep cool in hot environments

Proportionality shorter limbs —> less surface area → less heat loss → keep warm in cold environments

Clinal Variation

Cline= gradual change in trait frequencies over geographic space

EX: blood types around the world

Evolution of Blood types

Clinal distributions tend to be impacted by:

• Gene flow
• isolation -bu-distance
• Genetic drift
• Founder effect
• Sometimes natural selection

Ex: small pox

• The majority of genetic variation in human populations is NOT adaptively significant

Example of Clinal Variation:

Non- Binary Sex

• Turner syndrome= 1X or partial of a second x
• Klinefelter syndrome= XXY

This occurs via non-disjunction where the chromosomes don’t properly separate during mitosis resulting in 1 extra or loss of 1

• SRY gene and/or crossing over
• Sex as a biocultural phenomenon

Biocultural = biological variation

Quiz Review:

CONtNTINUED…

One -Drop-Rule: if you had even just one drop of non-white blood you were considered to be not white

Modern Synthesis

• Population of human variation
• Frequencies + variation rather than typology
  - typology: the idea of classifying a race based on checklist qualities
• Polygenic traits (continuous variation)
• Human variation impacted by evolutionary forces
• Genetics

Concordance: do traits show the same geographic patterns of variation

• Human variation is non concordance

EX: black people with blonde hair in Melesan

Descrete: specific categories [ex: height] where you could draw a line of difference [this person is short and this person is tall]

• Could you draw a line on the map that differentiates the traits between groups?

***Height is a continuous pattern***

Example: Sickle Cell

• The sickle cell allele has a really high frequency in black populations
• BUT it’s also eally common in Greece

→ doesn’t follow the held belief that it pertains to a race

a.k.a it is not descrete

Human Genetic Variation

• Humans share 99.9% of DNA
• Two humans from different countries are more similar to each other genetically than two chimpanzees from populations separated only by a river
• 90% of genetic variation within groups, only 10% between

Isolation-by-distance model

The closer you are geographically the more similar you are bound to be versus the more distant you are the more likely there is to be some genetic difference

Out-of-Africa model

If you were to look at all the genetic diversity in humans, most of it is found in Africa and then varies as it spreads out

• Your closest genetic twin is your sibling
• For the fraternal twins that look to be of opposite race it raises the question: are our siblings actually our closest genetic twin or is it just what we socially think?

Skulls

• Attempted to use skulls to show there was discrete difference between groups
• Confirmation bias and sampling errors
• Didn’t properly sample and therefore results could not be applied to the general population
• They also ignored skulls that didn’t fit into preconceived categories

Cultural Variation in Racial Classifiaction/Traits

• Scientist argued how many races there were
• One-drop-Rule around the world

Ex: argument of whether Obama was black or white

• Rwandan genocide- Hutis vs Tusis
• Holocusts: classified Jews based on traits associated with them
• Irish + Italians were not considered white at first but now aare
• Racial classification changed over time
• Basketball used to be considered a Jewish-dominated sport compared to now
• Idea that some races have athletic biological advances

→ Skin color, ancestry, blood types, cranial dimensions etc. were all used to classify racial groups at some point or another

• What we use to classify racial groups changes overtime due to social interpreatitions

Dangers of Biological Race Concepts

EX: sickle cell was believed to be a black disease and therefore couln’t affect other races

• A white girl went to the hospital with sickle cell anemia and they didn’t even think to check for it due to this way of thinking

EX: cystic fibrosis is more commonly found in european nations but is still found in other races

• Hasn’t been studied enough in other races and therefore many non-white people have been underdiagnosed
• For a long time , it was believed that black people didn’t experience the same degree of pain as white people did which greatly affected how either race recieved treatment

Culture can Impact Biology

• African-Americans tend to have higher risk for blood pressure and/or heart disease
• When it was analyzed more it was found that groups that were discriminated more had higher tendencies of blood pressure in comparsion to those that didn’t experience this

Human Adaptation: Skin Color

Melanin: Pigment that helps determine skin color

• Melanocytes= cells that produce melanin
• Natural protection against UV radiation
• Skin color varies by latitude
• Populations near the equator are more likely to have darker skin due to the climate

Hypothesis: Skin Cancer

• Melanin helps prevent skin cancer

Idea: Darker skin → Protection from UV rays → less risk of skin cancer

• Doesn’t make sense from a selective standpoint

Folic Acid Hypothesis

• Can be destroyed by UV rays
• Low folic Acid
• Birth defects
• Decreased sperm production
• Selection for melanin

Vitamnin D Hypotheis

• UV helps with production
• Nutrient absorption
• Deficiencies lead to
• Increased risk of some infections
• Rickets
• Selection against too much melanin in low UV areas may lead to not getting enough vitamin D as needed