ANP 206 #1

Adaptation

• The process of successful interaction

between a population and an

environment

• We do this in a number of ways, both

culturally and biologically, and all of

these decisions mutually affect one

another

Biocultural evolution

The interaction between biology and culture in shaping human evolution and variation.

Comparative approach

• Comparing human populations to determine common and unique behaviors or biological traits (i.e., variation).

• How and why do human groups differ from one another?

Holistic approach

takes into consideration all aspects of

human existence” to understand human

variation and evolution (Relethford p. 5). A

holistic approach to anthropology includes

all four major subfields (linguistic,

biological, cultural, and archaeological

anthropology

List and define the five subfields of Anthropology

Cultural, Medical, Linguistic, Archaeological, and Biological

Cultural Anthropology

Medical Anthropology

Linguistic Anthropology

Archaeological Anthropology

Biological / Physical Anthropology

Anthropology is..

List and define the examples of different (sub-)subfields of Biological Anthropology

Primatology, Paleoanthropology, Molecular, Morphological

Primatology

Uses primates to investigate:

- Variation

- Our place in nature

- Models

- Ecology

- Behavior

- Morphology

Paleoanthropology

Uses fossil remains to:

• Reconstruct behavior

• Understand evolution of human form

• Ask how, when and why human evolution occurred

Molecular human variation

Examines human variation at the molecular/genetic level

Morphological human variation

Examines variation in physical form and structure.

List and describe the four steps of science

Fact

A verifiable truth.

Scientific facts must be observable in nature.

Hypothesis

An explanation of observed facts that must be testable.

Theory

A set of hypotheses that have been tested repeatedly and have not been rejected.

Important Wrobel point:

You do NOT prove a theory—you fail to reject it.

Testability

A hypothesis must be falsifiable

Redi's Maggot Experiment

Step 1 — Observation

Maggots were commonly observed on rotting meat.

Question: Where did they come from?

At the time, spontaneous generation was an explanation. ANP206_Part 1 Lecture 1

Step 2 — Hypothesis

Redi proposed:

IF maggots come from eggs laid by flies,

THEN maggots should not form on rotting meat untouched by flies. ANP206_Part 1 Lecture 1

Step 3 — Test

He compared meat under conditions that differed in whether flies could access it.

Conclusion

Redi's conclusion was deliberately narrow:

Spontaneous generation occurs only in some circumstances.

He did not conclude that all spontaneous generation was impossible because his experiment only tested a particular situation involving maggots. The hypothesis continued to be tested and refined for roughly two centuries as new evidence—including microscopy—became available. ANP206_Part 1 Lecture 1

Step 4 — Theory

The lecture connects the later theoretical development to Louis Pasteur in 1859

Cultural context before Darwin

The lecture emphasizes that European thought was strongly influenced by classical ideas, folklore, resistance to change and essentialism.

The example of Giordano Bruno illustrates how challenging accepted explanations could be dangerous; the lecture summarizes the attitude toward change as:

“Change? Bad. Very very Bad.”

Essentialism

Everything is reducible to fundamental “types.” This conflicts with evolution because evolution requires populations/species to change through time rather than representing permanently fixed types

Plato's Allegory of the Cave (Essentialism)

The underlying idea is that observed variation can be viewed as imperfect versions of an underlying ideal or essential form

Great Chain of Being (Essentialism)

Nature was conceptualized as a fixed hierarchy.

Rather than organisms representing populations capable of evolutionary change, each type occupied a particular position in an ordered chain.

Binomial nomenclature

A naming system using:

Genus + species

Example:

Homo sapiens

Type specimen

The specimen serving as the reference example for a named biological type/species

Killing feature

A distinctive characteristic used to distinguish one species or taxonomic group from another.

EX The Bone of Contention

Nested hierarchy

Organisms are placed inside progressively broader categories.

Evolution gives this structure meaning because nested similarities can represent shared ancestry: organisms sharing more recent common ancestry should be nested more closely together.

Wrobel notes that Linnaeus was the first to classify humans with other animals and specifically with primates

Evidence that challenged essentialism

Fossils

Fossils included familiar animals AND surprising animals no longer living.

This suggested:

The world was not always as it is today → things change.

Dodo/extinction

Extinction itself demonstrated change.

If species can disappear, the Great Chain cannot be completely immutable

Explain Buffon’s and Lamarck’s proposals about how variations occurred in nature

Buffon

Proposed microevolution, although not creation of new species; species remained connected within a chain.

Lamarck

Proposed inheritance of acquired characteristics.

His mechanism involved use and disuse of body parts.

Traditional example: giraffes.

An organism changes a structure through its use during life → that acquired change is inherited by offspring.

Explain how each of the following ultimately influenced Darwin in constructing his

Theory of Evolution:

-his journey on the Beagle

-Lyell’s Geological Principles

-Breeding programs

-Malthus

Beagle — 1831–1836

Darwin observed intraspecies variation.

His major conclusion:

Variation is the norm in nature.

Lyell's Geological Principles

Three ideas:

- Earth is very old

- Change is constant

- The rules stay the same

Conclusion:

Change occurs over vast time scales.

Breeding programs

Breeders deliberately select desirable traits.

Humans = selection agents

Conclusions:

- Variations are inherited.

- Individuals don't evolve or change in the Darwinian population sense.

Malthus

Observation:

More young are born than reach adulthood.

Darwin's takeaway:

Nature selects by killing.

These observations provided Darwin with the pieces needed for natural selection.

Define:

-Selection

-Adaptation

the Darwinian Evolution

Change in the genetic composition of a population during successive generations, resulting from natural selection acting on genetic variation among individuals and potentially resulting in new species.

The key sequence:

Variation → selection → differential reproduction → population changes → adaptation/evolution

Not every biological variation is an adaptation. For something to be an adaptation in the Darwinian sense, it must relate to selection, not merely be a difference that exists.

Define the “comparative approach” and describe how it can provide explanations of

why specific biological differences and similarities between groups evolved

List the four primary sources of evidence for evolution, and be able to explain how

each provides evidence that evolution has occurred (or is occurring).

1. Fossil record of change in earlier species

Shows sequential change through time/stratigraphy.

2. Chemical and structural similarities of related life forms

3. Recorded genetic changes in living organisms over many generations

4. Geographic distribution of related species

DNA

The genetic material serving as the blueprint for development of the individual. Its molecular code controls protein synthesis.

Gene

The sequence of DNA that codes for one protein—this is the lecture's wording. ANP206_Part 1 Lecture 2

Chromosome

DNA is organized into 23 paired chromosomes, located in the cell nucleus. ANP206_Part 1 Lecture 2

RNA

The intermediate molecule used to transmit information from DNA toward protein production.

Central Dogma

DNA → RNA → protein

DNA serves as the template for transcription of RNA, which is then translated into protein.

PROTEINS

Amino acids

The smaller molecules composing proteins

Codon

Three bases coding for an amino acid.

There are four bases and therefore:

4 × 4 × 4 = 64 possible three-base combinations, allowing redundancy. ANP206_Part 1 Lecture 2

Transcription

Transcription = production of mRNA from DNA.

Basic concept:

DNA opens → DNA sequence serves as template → corresponding mRNA is produced → mRNA information can be translated into protein.

The sequence matters because DNA codes for the sequence of amino acids, which determines proteins

Translation

The ribosome reads mRNA codons and attaches corresponding amino acids to the growing protein chain.

When the ribosome reaches the end, the protein is finished

Noncoding DNA

About 98% of DNA is noncoding, meaning it is not directly translated into protein.

Know all five:

Regulatory regions: Control when and where genes are turned on/off.

Structural functions: Maintain chromosome stability and organization, including centromeres and telomeres.

Transposable elements: Mobile DNA sequences that can affect genome evolution and gene regulation.

Noncoding RNAs: Functional RNAs that regulate gene expression.

Evolutionary raw material: Sequences without an obvious current function can provide material for evolutionary innovation

Replication

DNA:

1. Unzips between bases.

2. Each strand acts as a template.

3. Complementary bases reconstruct the missing half.

4. DNA can therefore copy itself because of base complementarity.

Mitosis

Division of body cells into daughter cells.

In humans:

46 chromosomes → copied to 92 → separated → two cells containing 46 chromosomes each.

Meiosis

Mutations

Mistakes in DNA copying.

Substitution

One base substituted for another.

Insertion

Addition of one or more nucleotide bases.

Deletion

Loss of one or more nucleotide bases.

Frameshift

Insertion/deletion changes the reading frame unless the number of bases involved is a multiple of 3.

This makes subsequent codons incorrect and can produce a protein that is:

• Too short

• Too long

• Made with incorrect amino acids

Explain the reasons why mutations (relatively) rarely lead to a serious problem.

1. Redundancy

There are 64 possible codes but only 20 amino acids, so different codons can produce the same amino acid. ANP206_Part 1 Lecture 2

2. Noncoding DNA

About 98% of DNA is noncoding, making it likely that mutations occur outside protein-coding sequences.

3. Neutral inheritance

Many noncoding sequences (Like introns) don't strongly affect survival/reproduction, so they can be inherited neutrally. 

Define and know the listed attributes of mitochondrial DNA (mtDNA)

• Located in mitochondria, not nuclear chromosomes

• Circular

• 37 genes

• Little noncoding DNA

• Maternally inherited

• Mutates about 10× faster than nuclear DNA

Haploid, Diploid, Zygote, Genome

Diploid

A full set of 23 pairs of chromosomes.

Haploid

Half set: 23 chromosomes.

Eggs and sperm are haploid.

Zygote

The fertilized egg cell formed when two haploid genomes merge into one diploid cell.

Genome

A complete complement of genetic material from an individual

Alleles

Allele

Different versions/copies of genetic information at the same location. Dominant

An allele whose effect appears when present with another allele. Recessive

An allele whose effect is masked in a heterozygote by a dominant allele.

Mendel's pea experiments allowed recognition of dominant and recessive alleles

Mendel's Two Laws

1st “Law” = Segregation

–Based on monohybrid crosses (looking at inheritance of one trait)

–During reproduction, the two copies of a gene segregate from one another and only one is passed on

–Model crosses with Punnett Squares

• 2nd “Law” = Independent Assortment

–Based on dihybrid crosses (looking at inheritance of 2 traits at once)

–Segregation of one trait is not dependent/contingent on the segregation of another (they are independently assorted)

–Can model with Punnett Square

Define and explain the ways in which variation is created in offspring:

Random segregation

Which maternal/paternal copy of each chromosome enters a gamete is random.

Independent assortment

Different chromosome/allele combinations are independently distributed.

Crossing over

Before chromosomes separate during meiosis—not mitosis, chromosome pairs line up and exchange genetic material.

This further increases genetic diversity.

Simple vs. Complex Traits

• Simple trait

Follows relatively straightforward Mendelian inheritance.

• Complex trait

Affected by more than one gene (polygenic).

Most traits are complex.

Lecture examples:

• Eyes

• Skin color

• Height

Regulatory & Homeobox Genes

• Regulatory genes

Control expression of other genes.

Instead of simply coding for structural proteins, their products can:

• Turn genes on

• Turn genes off

• Fine-tune how much genes are expressed

• Homeobox/Hox genes

Produce proteins that bind DNA and switch transcription on/off.

They act as master switches, determining:

• Cell fate

• Growth

• Development

They can control:

1. Concentration

2. Location

3. Timing

4. Target-gene specificity

Because they organize the body plan, mutations in Hox genes can have huge phenotypic effects.

Continuous Variation

Most complex traits aren't discrete; they're continuous.

Produced through interaction between:

Genes + environment

→ often produces a normal distribution.

The more loci involved, the more the trait resembles a normal curve, while environmental influences blur distinctions between categories.

Pleiotropy

A single gene influences multiple traits.

Wrobel's example: SHH (Sonic Hedgehog), which affects multiple aspects of development.

Heritability

An estimate of the total variance of a trait caused by genetic variance rather than environmental variance.

Critical point:

Heritability is not inherent to the trait. It applies to a particular population in a particular environment.

Microevolution

Change in allele frequency in a population from one generation to the next

Population genetics

Study of the total pattern of genetic variation within a biological population.

Breeding population

The proportion of a population that chooses mates from within that group

Census population

The actual total population. It is always larger than the breeding population

Genotype frequency

Number of individuals with a particular genotype divided by the total number of individuals.

Example:

• AA = 0.49

• AB = 0.42

• BB = 0.09

These are genotype frequencies because AA, AB, and BB are combinations of alleles

Allele frequency

Relative proportion of each allele in the population.

Example:

• A = 0.70

• B = 0.30

These are allele frequencies because A and B are individual alleles, not genotypes. ANP206_Part 1 Lecture 3

Phenotype frequency: An indirect measure of genotype based on observable traits. ANP206_Part 1 Lecture 3

Easy recognition

AA, AB, BB → genotype frequencies
A, B → allele frequencies

Phenotype frequency

An indirect measure of genotype based on observable traits

Hardy-Weinberg Equilibrium

Hardy-Weinberg equilibrium is a method for determining the expected genotype frequencies in the offspring generation based on the allele frequencies of the parent population. The equation is:

p² + 2pq + q² = 1

Where:

• p and q = allele frequencies

• p² = AA

• 2pq = AB

• q² = BB

Five Hardy-Weinberg assumptions

H-W assumption	If broken...
No mutation	Mutation introduces new alleles
No selection	Natural selection changes reproductive success of alleles/genotypes
No migration	Gene flow moves alleles between populations
Large population	Small populations experience stronger genetic drift
Random mating	Mate choice changes genotype frequencies

Wild type allele (vs. mutant allele)

Mutation: Introduces new alleles into a population.

Wild-type allele: Original, common, or "normal" version of a gene.

Mutant allele: New or "abnormal" version of the gene

Natural Selection generally does not affect mtDNA. How do anthropologists use that to their advantage?

According to your lecture, mutations in mtDNA used for ancestry tracing do not affect phenotype and therefore are not subject to natural selection in the example presented. This makes mtDNA useful for tracing ancestry because changes can accumulate without being strongly filtered by natural selection.

Natural Selection

Natural selection: Filters existing genetic variation by changing the likelihood that different alleles are passed to the next generation.

Important:

Natural selection does NOT create variation.
It changes the relative frequencies of existing alleles

Fitness

An organism's probability of survival and reproduction, measured by the relative contribution of a genotype to the next generation

Heat Stress

Heat stress: Occurs when the body isn't removing heat quickly enough.

Vasodilation: Expansion of blood vessels, which increases heat loss through convection.

Vasoconstriction: Narrowing of blood vessels, which reduces blood flow near the body's surface and helps conserve heat.

Evaporation: Heat loss when water/sweat changes into vapor.

Convection: Transfer of heat through surrounding air molecules. ANP206_Part 1 Lecture 3

Bergmann's Rule

When two mammals have similar shapes but different sizes:

• Smaller body → higher surface-area-to-mass ratio → loses heat faster

• Larger body → lower surface-area-to-mass ratio → retains heat better

Therefore:

Warm climate → smaller body advantageous
Cold climate → larger body advantageous

The lecture emphasizes that population weight, rather than height, shows the clearer relationship with mean annual temperature

Allen's Rule

Allen's Rule

This is about shape/appendages.

A more elongated body has a higher surface-area-to-mass ratio and therefore loses heat more easily.

Thus:

Warm climate → longer appendages
Cold climate → shorter appendages

The lecture specifically mentions tails, limbs, ears, and noses tending to be shorter in cold regions. ANP206_Part 1 Lecture 3

Don't confuse them

Bergmann = Body SIZE

Allen = Appendage SHAPE

Molecular Mimicry

Molecular mimicry: A disease organism possesses surface molecules that mimic molecules found on the host's cells, making it harder for the immune system to recognize the organism as foreign. ANP206_Part 1 Lecture 3

Smallpox example

The lecture says smallpox has surface molecules that mimic A antigens on red blood cells.

Therefore:

• Blood type A or AB → more difficulty recognizing the virus as foreign

• Greater susceptibility/severity in the lecture example

Smallpox existed in Asia and Africa for thousands of years, and these regions show a lower frequency of the A allele, which the lecture presents as evidence of natural selection affecting ABO frequencies. ANP206_Part 1 Lecture 3

Lactase Deficiency

Lactase deficiency/lactose intolerance: An older child or adult lacks the ability to produce sufficient lactase, the enzyme needed to digest lactose.

Humans normally produce lactase as infants. The lecture describes turning lactase production off around age four after nursing as the wild-type condition. ANP206_Part 1 Lecture 3

Without lactase, consuming milk can cause:

• Diarrhea

• Cramps

• Intestinal problems

• Reduced caloric absorption

But some populations continue producing lactase throughout life.

Why natural selection?

The lecture associates adult lactase production with dairy farming:

Populations with a history of dairy farming → lower lactase deficiency.

Milk provided nutrition/calories, so the ability to digest it could provide an advantage in dairy-farming populations. ANP206_Part 1 Lecture 3

Skin Color

Melanin: Brown pigment responsible for most variation in skin lightness/darkness.

Melanocytes: Cells in the bottom layer of skin that produce/secrete melanin.

The lecture notes that people have the same number of melanin-producing cells but differ in the amount and clustering of melanin produced. ANP206_Part 1 Lecture 3

UV damage

High UV exposure can:

• Cause tanning

• Cause sunburn

• Damage DNA

• Increase skin-cancer risk

Higher melanin levels block more UV. ANP206_Part 1 Lecture 3

However, your lecture emphasizes an important limitation: skin cancer often occurs after reproductive age, meaning it may not exert a strong selective disadvantage. Severe sunburn and infection can affect fitness, though. ANP206_Part 1 Lecture 3

Vitamin D hypothesis

UV radiation is required for the skin to synthesize vitamin D, which is needed for proper bone growth. ANP206_Part 1 Lecture 3

Rickets: Disease resulting from insufficient vitamin D that causes poor bone development and bone deformation.

In women, pelvic deformation could interfere with childbirth and therefore affect reproductive fitness. ANP206_Part 1 Lecture 3

Selective pressures on skin color

Near equator/high UV:

More melanin can protect against:

• UV damage

• Sunburn

• Skin cancer

• Excess vitamin D in the lecture's hypothesis

Higher latitudes/low UV:

Lighter skin allows more UV penetration, helping produce sufficient vitamin D and reducing vitamin-D deficiency

Gene Flow

Gene flow: Movement of genes from one population to another.

Over time, gene flow tends to make populations more similar in allele frequencies. ANP206_Part 1 Lecture 3

Isolation by distance: Gene flow decreases as geographic distance increases.

Genetic distance: Measure of how genetically different populations are; smaller genetic distance means greater genetic similarity.

Irish Midlands example

Researchers examined 31 Irish counties. Four genetically distinctive counties were in the Irish Midlands.

Those counties had a small genetic distance from Scandinavian populations, suggesting historical admixture/gene flow with Vikings.

So:

Vikings entered Ireland → interbred with local populations → Viking alleles entered Irish populations → gene flow

Genetic drift

Random change in allele frequency from one generation to the next.

The smaller the population, the stronger the effect of drift.

Small populations can have alleles reach fixation quickly

Fixation

An allele reaches a frequency of 100%, so it is the only allele at that locus in the population

Founder effect

Occurs when a small number of individuals start a new population, with descendants derived from those founders. ANP206_Part 1 Lecture 3

The new population may have very different allele frequencies simply because the founders carried only a sample of the original population's variation.

Population bottleneck

major reduction in population size causes a reduction in genetic variation.

The lecture gives causes such as:

• Disease

• War

The Florida panther is shown as an example

Founder vs bottleneck

Founder → few leave and start a population
Bottleneck → existing population suddenly becomes very small

Both involve genetic drift.

Founder vs bottleneck

Founder vs bottleneck

Founder → few leave and start a population
Bottleneck → existing population suddenly becomes very small

Both involve genetic drift.

Non-Random Mating

Assortative mating: Mating based on phenotypic similarity or dissimilarity.

Inbreeding: Mating between biologically related individuals. This produces consanguinity and can be deliberate or random. ANP206_Part 1 Lecture 3

Demonstrations of Population Genetics:

1. Tay-Sachs disease

Explain how the specific circumstances of Ashkenazi Jews in Europe led to natural selection favoring the Tay-Sachs allele.

Explain why this is an example of Natural Selection.

Tay-Sachs is a genetic disease caused by the lack of an enzyme, resulting in accumulation of a fatty substance in nerve cells.

The homozygous recessive genotype is lethal, usually before age four in the lecture. ANP206_Part 1 Lecture 3

Why was the allele maintained among Ashkenazi Jews?

Your lecture considers several possibilities:

• Mutation? No — required mutation rate would be unrealistically high.

• Gene flow? Could explain introduction but not continued high frequency.

• Genetic drift/founder effect? Considered, but lecture argues population size/distribution doesn't adequately explain continued high frequency.

• Natural selection? Lecture's proposed explanation: heterozygotes received some protection against tuberculosis (TB). ANP206_Part 1 Lecture 3

Historically, Ashkenazi Jews were confined to urban ghettos, where they experienced particular TB exposure/selective pressure. The lecture notes relatively low TB rates compared with other European ethnic groups. ANP206_Part 1 Lecture 3

Why is this natural selection?

Because carrying one Tay-Sachs allele is presented as providing a fitness advantage under that historical environmental pressure.

Heterozygote → TB protection → greater survival/reproduction → allele maintained

Sickle Cell Anemia

Define:

Directional selection

Balancing selection (*note: does NOT mean 50/50 ratio!)

Infectious disease

Non-infectious disease

Relative fitness

HbS/HbS (SS) causes sickle cell anemia in the lecture.

Normally, because HbS is harmful in homozygotes, natural selection should reduce its frequency. Yet HbS reaches frequencies around 10–20% in certain environments, particularly those associated with falciparum malaria. ANP206_Part 1 Lecture 3

Definitions

Directional selection: Selection pushes allele frequencies primarily in one direction by favoring one genotype/allele over another.

Balancing selection: Selection maintains multiple alleles within the population.

Important:

Balancing does NOT mean 50/50.

Your lecture specifically gives approximately:

• S allele = 10–20%

• A allele = 80–90% ANP206_Part 1 Lecture 3

Infectious disease: Disease caused by an organic foreign agent such as a bacterium, parasite, or virus.

Non-infectious disease: Not caused by an organic foreign substance.

Therefore:

• Malaria = infectious

• Sickle cell anemia = non-infectious/genetic ANP206_Part 1 Lecture 3

Relative fitness: How successfully one genotype survives and reproduces relative to other genotypes in that particular environment.

Compare the relative fitnesses of each genotype in malarial vs. non-malarial environments Sickle Cell Anemia

Fitness in a malarial environmentAS

Highest relative fitness

• Doesn't develop sickle cell anemia

• Resistant to malaria

AA

Lower fitness than AS because:

• No sickle cell anemia

• But susceptible to malaria

SS

Very low fitness because:

• Develops sickle cell anemia

The lecture gives a striking example:

For every 100 AS individuals surviving to adulthood, about 88 AA and only 14 SS survived to adulthood in the cited African study. ANP206_Part 1 Lecture 3

So in malaria:

AS > AA > SS

That's heterozygote advantage/balancing selection.

In a non-malarial environment

The advantage of AS largely disappears because malaria isn't exerting selection.

But selection against SS remains because sickle cell anemia is still harmful.

Therefore, the S allele tends to decrease.

Environment changes fitness

This is one of the most important concepts:

A genotype isn't universally "fit."
Fitness depends on the environment.

Malaria present → AS advantage → HbS maintained

Malaria absent → AS advantage disappears + SS still disadvantaged → HbS decreases

How has culture acted to shift allele frequencies of Sickle cell

The lecture calls this a biocultural interaction.

Human habitation and agriculture changed environments in ways that favored the mosquitoes transmitting malaria.

So:

Cultural/agricultural change → mosquito habitat changes → malaria pressure changes → relative fitness changes → HbS allele frequency changes.

Using a case example, how and why is the rate of sickle cell anemia different

among African Americans vs. European Americans and Africans?

Explain why this is an example of Natural Selection

15. African Americans, Africans & HbS

Many enslaved Africans brought to the Americas came from African regions with relatively high HbS frequencies.

However, the lecture says HbS became 50–75% less frequent among African Americans. ANP206_Part 1 Lecture 3

Why?

1. Less malaria selection

Malaria-carrying mosquitoes survive best in tropical regions. Much of North America therefore had less selection favoring AS heterozygotes. ANP206_Part 1 Lecture 3

2. Selection against SS continued

Sickle cell anemia remained harmful even without malaria.

So:

Benefit of AS decreases + cost of SS remains → HbS frequency decreases.

The lecture notes HbS frequencies among African Americans are highest in the Southeast, where historical malaria exposure was greater. ANP206_Part 1 Lecture 3

3. Gene flow

Gene flow from European-derived populations, which had very low HbS frequencies, further reduced HbS frequency among African Americans.

African American populations with historically less non-African admixture tend to have higher HbS frequencies

16. Yanomami — Gene Flow vs Genetic Drift

This example shows how social structure can influence microevolution.

Fission

Fission: When an area becomes too populated, groups split up and spread out.

Yanomami villages tend to split along family lines.

Because the resulting groups are small, genetic drift becomes stronger.

The lecture describes fission as similar to a founder event. ANP206_Part 1 Lecture 3 ANP206_Part 1 Lecture 3

Fission → smaller population → more drift

Fusion

Fusion: Two groups merge when populations become too small or outside pressures such as warfare/famine become too strong.

Fusion → larger population → reduced effect of drift

Exogamy

Exogamy: Tendency to choose mates from outside the local population.

This produces:

Exogamy → mating between villages → gene flow → populations become more genetically similar

It also counteracts genetic drift. ANP206_Part 1 Lecture 3

Polygyny

Polygyny: Marriage system in which one male has multiple wives.

The lecture explains that this means some males contribute much more genetically to the next generation than other males. ANP206_Part 1 Lecture 3

That effectively reduces the number of individuals contributing genes to the next generation, making random changes in allele frequencies more consequential.

Fst

Fst: A statistic measuring the amount of genetic differentiation between populations.

For your exam, know the scale:

• Fst = 0 → populations have the same alleles at the same frequencies.

• Fst = 1 → populations are completely differentiated: individuals within each population are homozygous for the same alleles, but different populations are homozygous for different alleles.

• Standard criterion used for a "race" in some nonhuman literature: Fst = 0.25–0.30

• Human sample in your lecture: Fst = 0.156. ANP206_Part 1 Lecture 4

Easy way to remember

Fst 0 = same
Fst increases = populations increasingly genetically differentiated
Fst 1 = completely differentiated

Your lecture uses the human Fst value as part of its discussion of why the population definition of race does not fit humans well.

Discordance

Discordance: The non-agreement in the distribution of genetic traits.

Different traits have different geographic distributions because traits can vary independently of one another. ANP206_Part 1 Lecture 4

Why does this matter for race?

Suppose you try to divide humans into races using:

• Skin color

• Blood type

• Hair characteristics

• Facial characteristics

The geographic boundary you draw using skin color may not match the boundary you get using blood type.

So:

Trait A's distribution ≠ Trait B's distribution

That's discordance.

The diagram on page 3 illustrates this with multiple overlapping boundaries: depending on which trait you select, you would divide the population differently.

Trait Definition of Race

The lecture defines it as:

A race is a division of a species that differs from other divisions by the frequency with which certain hereditary traits occur among its members. ANP206_Part 1 Lecture 4

In simpler terms:

Choose hereditary traits → compare their frequencies → divide humans into groups based on those traits.

Why doesn't it work?

There are two major problems.

1. Which traits should you use?

There are almost endless possibilities.

2. How many traits should you use?

Different combinations and numbers of traits produce different racial classifications.

And this leads directly to discordance: different traits have different distributions because they vary independently. ANP206_Part 1 Lecture 4

Exam answer

The trait definition fails because the choice and number of traits used are arbitrary, and different traits have discordant distributions. Therefore, different traits produce different racial boundaries