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GWU / Sociology / ANTH 1001 / What is a archaeology?

What is a archaeology?

What is a archaeology?

Description

School: George Washington University
Department: Sociology
Course: Introduction to Biological Anthropology
Professor: Alison brooks
Term: Fall 2017
Tags: Biological, Anthropology, Midterm Study Guide, and Studyguide
Cost: 50
Name: ANTH 1001 - Midterm Studyguide
Description: This study guide covers chapters 1-6 in Professor Barr's Intro to Biological Anthropology class.
Uploaded: 02/17/2018
18 Pages 11 Views 15 Unlocks
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Ch.1: Intro to Biological Anthropology


What is a archaeology?



Anthropology and its Subfields

● Anthropology​ = study of humankind in all its forms

○ What makes human animals unique is culture

○ Culture​ = sum total of learned traditions, values, and beliefs that groups of people (and a few species of highly intelligent animals) possess.

● 4 Subfields: 

○ Biological anthropology​ = the study of humans as biological organisms, considered in an evolutionary framework; sometimes called physical

anthropology.

■ Hominin​ = member of the primate family Hominidae, distinguished by bipedal posture

○ Cultural anthropology​ = the study of human societies in a cross-cultural perspective We also discuss several other topics like who stay in Italy and start running the homeland/goverment?

○ Linguistic anthropology​ = the study of language and its origins, structure, and use

○ Archaeology​ = the study of material remains (e.g., artifacts) of past human cultures

The Scope of Biological Anthropology


What is a osteology?



● Biocultural anthropology​ = the study of the interaction between biology and culture ● Paleoanthropology = the study of fossil records

○ Early fossils give clues about how, where, and why hominins evolved millions of years later

● Osteology​ = study of the skeleton

● Paleopathology and bioarchaeology​ = study of disease in ancient human populations ● Forensic anthropology​ = study of identification of skeletal remains and the means by which the individual died

● Primatology​ = study of anatomy, physiology, behavior, and genetics of living and extinct nonhuman primates Don't forget about the age old question of What is the inorganic elements required by organisms for normal growth, reproduction, and tissue maintenance?

● Human biology​ = subfield of biological anthropology dealing with human growth and development, adaptation to environmental extremes, and human genetics.

Ch.2: Origins of Evolutionary Thought

● The scientific method​ – process that involves deduction and observation; formulation of a hypothesis, experimentation, and collection of evidence (data).


What is the scientific method?



Don't forget about the age old question of Ionic bonds means what?

● Empirical​ – based on knowledge gained through observation

● Falsifiable​ ​– defining trait of science: able to be shown to be false We also discuss several other topics like what is the formula of TFP?

● Paradigm​ – a conceptual framework useful for understanding a body of evidence ● Evolution​ – change over time

~ The Early Thinkers

Ancient Greek Ideas on Biological Evolution: 

● Anaximander​:​ sought natural causes for biological and other earthly phenomena (6th Century BC)

○ Had a notion of change​—that humans and animals descended from fish

● Plato​:​ concept of the “eidos,” an abstract ‘form’ that is imperfectly imitated in the real world (427 - 347 BC) Don't forget about the age old question of Classical realism is a theory of what?

○ Species have a defining “essence” that is fixed​ and unchangeable

● Aristotle​:​ appreciated organic diversity (384 - 322 BC)

○ Organized and classified organisms​ into “scala naturae” or Great Chain of Being, with humans at the top

The European Middle Ages: conceptualization of a static world: 

● Fixity of species

● Great chain of Being

● Argument from design

● Recent origin of the earth [Archbishop James Ussher (1581-1656)]

Evolutionary Thought Prior to Darwin: 16th – 19th Centuries: 

● Li Shih-Chen ​(1518 – 1593)

○ Chinese naturalist, believed organisms are influenced by their environments ○ Binomial system of naming organisms

○ Hierarchial classification scheme

● Galileo Galilei ​(1564 – 1642)

○ Established a systematic empirical approach to looking at natural phenomena ○ Confirmed Copernicus’ idea that the earth was not​ the center of our celestial system; the notion of change becomes more acceptable

● John Ray​ (1672 – 1705)

○ Defined species as a group of organisms that can reproduce with each other ○ Recognized that species share similarities with other species – used the genus to acknowledge this fact

● Carolinus Linnaeus​ (1707 – 1778)

○ Systema Naturae

○ Binomial System​ – a hierarchical system of Classification with organisms grouped based on similarities If you want to learn more check out What is nucleic acid and its function?

○ Linnean system – the classification scheme we use in the biological sciences today ○ Taxonomy​ – the science of classifying and naming living things that Linnaeus invented

○ Binomial nomenclature​ ​– two-level genus-species labels

○ Taxon​ ​– any unit of this formal hierarchy

● Compte De Buffon​ (1707 – 1788)

○ Histoire Naturelle (1749)

○ Animals that migrate to new climates often change in response to new environments

○ One of the first to suggest that the external environment​ is important agent of biological change; variation observed in organisms may reflect environmental influences

● Jean Lamarck​ (1744 – 1829)

○ Philosophie Zoologique (1809)

○ First to propose a mechanism of evolutionary change to explain biological diversity

○ Recognized that organisms interact in a dynamic way with their environments, important for producing evolutionary change

○ Theory of inheritance of acquired characteristics:

■ Use or disuse

■ Inheritance

■ Interactions between individuals and their environments are important ■ Proposed incorrectly​ that evolutionary change occurs during the lifetime of single individuals (e.g. falsely thought giraffes could stretch their necks to permanently increase length and pass on the long neck genes)

● Georges Cuvier​ (1769 – 1832)

○ Described changes in the assemblages of biological organisms that were tied to changes in rock layers of the Paris Basin

○ Catastrophism​ – environmental catastrophes cause biological extinctions, which account for changes in fossil organisms

● Charles Lyell​ (1797 – 1875)

○ Principles of Geology (1830 – 1833)

○ Uniformitarianism​ = the theory that the same gradual geological process we observe today was operating in the past. 

○ Provided the time frame needed for the acceptance of organic change

Pre-Darwin Developments: 

● Appreciation of diversity in the natural world, and methods of classification ● Concepts of species

● Notion of organic change

● Environment as an important agent of organic change

● Ancient origin of the natural world

→ Time was right for someone to put it all together

Charles Darwin 

● Came from a rich family, high social rank

● Family sent him to medical school, but he didn’t like it so he left

○ Went to pursue theology and took an interest in botany & the natural sciences ● Scientific expedition (5 year voyage) on the HMS Beagle

○ Left England → South America → Galapagos Islands → Australia → Africa → other stops → Back up North

○ Brought back specimen

● His evolutionary ideas after the voyage went against dominant Christian beliefs at the time, causing him to hold back on publishing his theories for years

Experiences that influenced his thinking:

● Observation of biological diversity in plants/animals

● Earthquake in Chile à interest in geology: Earth’s surface is constantly moving and changing

● Fossil bones in Argentina à extinction of animals

● Diversity in finches on the Galapagos Islandsà adaptation differences ○ variations in finches matched variations in the available food on these different islands

○ Biogeography​ – distribution of animals and plants on Earth

○ Adaptive radiation​ – the diversification of one founding species into multiple species and niches

○ Natural selection​ – differential reproductive success over multiple generations ○ His reading of Thomas Malthus’ book

■ Idea that human population has potential to increase exponentially, only if it goes unchecked, known as the “struggle for existence”

■ Darwin concluded that individuals with advantageous traits will survive in this struggle for existence, and will reproduce successfully à “survival of

the fittest”

■ Survival of the fittest DOES NOT mean “strong.” Sometimes it is the weak that survives. For example, in times of famine, it is the smaller ones that will survive.

■ Observation of power of artificial selection

■ Selective breeding (e.g.. wolves became different types of dogs through generations of breeding)

Timeline

● 1836 – Darwin returns from voyage

● 1844 – Darwin prepares his first lengthy “sketch” on his theory of evolution by means of natural selection

● Alfred Wallace in Southeast Asia mailed Darwin about the same idea, that he had theorized independently à event that made Darwin realize it was time to publish his ideas ● 1858 – Darwin and Wallace present their ideas to the Linnean Society in London

“On the Origin of Species” (1859)

Main Themes: 

● Biological evolution is a fact

● Common descent, with modification

● Gradualism

● Natural selection is the mechanism of evolution

● Natural Selection occurs when there is:

○ Variability

○ Heritability

○ Struggle for existence

○ Differential reproduction/ survivability

Definitions:

● Fitness​ – reproductive success (number of offspring)

● Adaptation​ – changes in response to new or varying environmental pressures ● Creation science ​– a creationist attempt to refute the evidence of evolution ● Intelligent Design ​– a creationist school of thought that proposes that natural selection cannot account for the diversity and complexity of form and function seen in nature

Ch.3: Genetics I, Cells and Molecules

The Cell

● Prokaryotes​ = single celled organisms, such as bacteria, in which the genetic material is not​ separated from the rest of the cell by a nucleus.

● Eukaryotes​ = a cell that possesses a well-organized nucleus

○ Nucleus​ = part of the cell in which the genetic material is separated from the rest of the cell by a plasma membrane

○ Cytoplasm​ = region within the cell membrane that surrounds the nucleus; contains organelles that carry out essential functions such as energy production, metabolism, and protein synthesis

● Somatic Cells​ = cells of the body that are not sex cells (e.g., body tissue cells) ● Gametes​ = sex cells

● Stem cells​ = undifferentiated cells found in the developing embryo that can be induced tp differentiate into a wide variety of cell types or tissues

Cell Anatomy

● Deoxyribonucleic acid (DNA)​ = a double-stranded molecule that is the carrier of genetic information

○ Inside nucleus

○ Stores and transmits information

○ Made up of smaller molecules called nucleotides

■ Primary Functions:

● Protein synthesis

● Replication

● Cellular respiration

DNA Structure

● Basic unit of DNA (and RNA) are nucleotides

○ Nucleotide​ = molecular building block of nucleic acids

■ consists of phosphates, sugar, and base

○ Base​ = variable component of the nucleotides that form the nucleic acids ● Each nucleotide contains 1 of 4 different bases

● Structural differences between 2 classes of bases: purines and pyrimidines ○ Purines (two fused rings):​ Adenine (A) and Guanine (G)

○ Pyrimidines (one single ring):​ Thymine (T) and Cytosine ©

○ Complementary pairing: 

■ A​ = T

■ C​ = G

■ Example:

● Original Strand: ATA GAT

● Complementary Strand: TAT CTA

● Complementary polynucleotide chains (base pairing) provides a mechanism by which the molecule can replicate itself

○ The sequence of nucleotide bases varies, and contains important genetic information

DNA Functions

● Replication​ (cell division)

○ DNA replication occurs during cell division, where original double-stranded molecules separate, forming unattached strands that are attracted to their

complementary strands.

○ Results in two identical copies of DNA molecule

○ Enzyme​ = complex protein that is a catalyst for chemical processes in the body ● Protein Synthesis​ (genotype to phenotype)

○ Genotype​ = underlying genetic makeup

○ Phenotype​ = physical outcome (e.g., green eyes)

○ Proteins are the workhouse molecules of biological organisms

■ Hemoglobin​ = protein molecule found in red blood cells that transports oxygen

○ Amino Acids​ = molecules that form basic building blocks of protein

■ Of the 20 amino acids, 9 are essential​, meaning they must be obtained from the protein in our diet

■ Amino acid subunits are linked together to form linear polypeptide chains ● Can be combined in different amounts and sequences to produce

different proteins

The Genetic Code 

● The system whereby the nucleotide triplets in DNA and RNA contain the information for synthesizing proteins ​from the 20 amino acids.

● Codon​ = a triplet of nucleotide bases in mRNA that specifies an amino acid or the initiation or termination of a polypeptide sequence

○ Transcription = occurs in the nucleus of the cell

■ Messenger RNA (mRNA)​ = strand of RNA produced during transcription that carries information of the gene from the nucleus to the cytoplasm,

where protein synthesis (translation) takes place

○ Translation = (protein synthesis) occurs in the cytoplasm

■ Transfer RNA (tRNA)​ ​= RNA molecules that bind to specific amino acids and transport them to ribosomes to be used during protein synthesis ● Because there are only 20 amino acids, many are specified by more than one codon sequence

○ Redundancy: many mutations are synonymous​, meaning they don't change the amino acid produced.

● Gene​ = sequence of DNA bases that carries information for synthesizing a particular protein, and occupies a specific chromosomal locus.

○ Protein synthesis occurs at ribosomes outside of nucleus, but DNA can’t leave the nucleus

DNA vs. RNA

● DNA: double stranded, deoxyribose sugar, Thymine base

● RNA: single stranded, ribose sugar, Uracil base

DNA Mutations

● Point mutations:​ AGC​ TCC CTA → AGG TCC CTA

● Duplication:​ ​AGC TCC CTA → AGC AGC TCC CTA

● Inversion​:​ AGC TCC CTA → CGA TCC CTA

● Deletions (frame-shift):​ AG​C TCC CTA T… → ACT CCC TAT

Ch.4: Genetics II, Mendelian Inheritance

Darwin’s Origin of Species:

● All organisms have descended with modification from common ancestors ● Mechanism for evolutionary change is the action of Natural Selection on individual variation

Missing Pieces to his theory:

● Source of individual variation

● Mechanism of inheritance

I. From Genotype to Phenotype

● Phenotype​ = the observable o detectable expression (e.g. appearance) of a trait. ● Genotype​ = the full set of genetic factors or alleles that interact in determining the phenotype.

● Homozygous​ = when two copies of the same genetic factor controlling a trait are present in an individual (True Breeding Lines).

● Heterozygous​ = when two different genetic factors for a trait are present in an individual (Hybrid).

● Structural genes ​= genes that contain the information to make a protein. ● Regulatory genes​ = genes that guide the expression of structural genes, without coding for a protein themselves.

● ABO blood type system​ = refers to the genetic system for one of the proteins found on the surface red blood cells, consists of one gene with 3 alleles: A, B, O. ○ This illustrates a straightforward relationship between genotype and

phenotype.

II. Mendelian Inheritance

Pre-DNA Concepts of Inheritance:

● Blending inheritance​ = parental contribution is averaged out, or blended, in offspring

○ BUT, this theory does not include a mechanism for preservation of traits; favorable mutations would get averaged out and lost.

Gregor Mendel (1822 - 1884)

● Undertook a systematic investigation of inheritance using very large numbers of pea plants

○ Cross fertilization via cross pollination

○ most plants are hermaphrodite (both both male and female organs)

○ Why Pea Plants?

■ 1. Easy to control pollination

■ 2. Shows variation in a number of different traits

■ 3. Pure breeding lines could be identified

● Demonstrated Particulate Inheritance

○ Particulate Inheritance​ ​= concept of heredity based on the transmission of genes (alleles) according to Mendelian principles.

○ Each hereditary characteristic is controlled by particulate unit factors (genus), which exist in pairs in individual organisms, one factor is

inherited from each parent.

○ These factors remain discrete and unchanged, regardless of its external appearance

● Dominance

○ When 2 different unit factors relate to a characteristic, only one is

expressed (dominant), while the other is not (recessive)

○ There must be two copies of the recessive gene present for the form to be expressed.

○ Recessive​ = in a diploid organism, refers to an allele that must be present in two copies (homozygous) in order to be expressed

○ Dominant​ = in a diploid organism, an allele that is expressed when

present on only one pair of homologous chromosomes

○ Codominant​ = in a diploid organism, two different alleles of a gene that are both expressed in a heterozygous individual.

III. Mendel’s Postulates:

1. Hereditary characteristics are controlled by particulate unit factors that exist in pairs in individual organisms.

a. The unit factors are genes, and chromosomes come in pairs in diploid organisms b. Each individual receives one copy of each chromosome from each parent: receiving one pair of unit factors from each parent.

2. When an individual has two different unit factors responsible for a characteristic, only one is expressed and is said to be dominant to the other, which is said to be recessive. a. In heterozygous individuals, the allele that is expressed is dominant. b. In Mendel’s experiments, round seed form was dominant to wrinkled seed form, and yellow seed form was dominant to green.

3. During the formation of gametes, the paired unit factors separate, or segregate, randomly so that each sex cell receives one or the other with equal likelihood. a. Mendel’s Law of Segregation​ = the two alleles of a gene found on each pair of chromosomes segregate independently of one another into sex cells during meiosis.

b. The Punnett Square allows us to illustrate possible genotypes of the offspring 4. During gamete formation, segregating pairs of unit factors assort independently of each other.

a. Mendel’s Law of Independent Assortment ​= genes found on different chromosomes are sorted into sex cells independently of one another.

2 Types of Sex Cells:

1) Somatic Cells

a) The cells of the body that are not sex cells

b) 23 chromosome pairs

c) Diploid​ = 2 copies of every chromosome

2) Sex cells (gametes)

a) Ova: egg cells produced in ovaries

b) Sperm: sex cells produced in male testes

c) 23 chromosomes

d) Haploid​ = having a single set of unpaired chromosomes

e) Zygote​ = union between a sperm and ovum (= diploid)

IV. Cell Division

Mitosis​ ​(somatic cells)

● 2 diploid cells result in 2 identical daughter cells (cloning)

I. Interphase

A. DNA replication

II. Prophase

A. 2 identical chromatids

III. Metaphase

A. Single file line

IV. Anaphase

A. Sister chromatids separate

V. Telophase

A. Results in 2 daughter cells (diploid) with identical copies

Meiosis​ (sex cells)

● Production of gametes, characterized by TWO rounds of division that result in 4 daughter cells, each of which contains 23 chromosomes (4 haploid cells)

● Fertilization restores the full complement of chromosomes (diploid # of 46) to the zygote

First Division:

I. Interphase

A. DNA replication

II. Prophase I

A. Crossing over (genetic recombination)

III. Metaphase I

A. Chromosomes align in homologous pairs; random assortment of

chromosome members

IV. Anaphase I

A. Chromosome pairs separate (reduction division)

V. Telophase I

VI. Interkinesis I

A. Two haploid daughter cells, which are genetically dissimilar; no

DNA replication

Second Division:

I. Prophase II

II. Metaphase II

A. Chromosomes line up single file

III. Anaphase II

IV. Telophase II

V. Daughter Cells

A. 4 haploid gametes, genetically dissimilar

Genetics Beyond Mendel:

● Sex Linkage​ (X-linked traits)

○ Controlled by genes on the X chromosome, more commonly expressed on males. As males (XY) have only one X chromosome, any allele will be expressed, whether dominant or recessive (e.g., red-green color blindness)

● Traits that do not follow Mendel’s Rules:

○ Polygenic Traits​ = ​many genes contribute to a single effect

■ Traits with quantitative (continuous) variation, influenced by two or more genes. (e.g., skin and eye color)

○ Pleiotropy​ = a single gene influences the expression of multiple traits simultaneously (e.g., Marfan Syndrome)

○ Types of Genes:

■ Structural

■ Regulatory

● Homeotic genes

● Humans and Chimpanzees share 99% similarity in their DNA;

differences must have emerged from very few changes in

regulatory genes with pronounced downstream effects

Ch.5: Forces of Evolution

Population​ = a group of organisms potentially capable of successful reproduction ● Largest reproductive population is the species

● Individuals of a population tend to mate within their group

● Population is the unit of evolution

Gene pool​ = the sum of all alleles carried by the members of a population Evolution​ = a change in allele frequencies in a population from one generation to the next Genetic equilibrium = no changes in allele frequencies (no evolution is occurring in population)

Hardy Weinberg: model of genetic equilibrium

● Used to determine whether or not evolutionary forces are operating on the population ● Measure observed genotype frequencies for specific traits, and compare them against predicted genotype frequencies assuming no evolution is occurring

● p^2 + 2pq + q^2 = 1

Forces of evolution​ = factors occurring in natural populations that cause changes in gene frequencies over multiple generations.

1. Mutation

a. Alteration in genetic material

b. Mutations are chance events, rare events

c. Adds variation to the gene pool, gives rise to new alleles

2. Natural selection

a. Alleles that confer an increased likelihood of survival to reproduction will be passed onto the next generation with greater frequency

b. Stabilizing: maintains a certain phenotype by selecting against deviations from it c. Directional: selection for greater or lesser frequency of a given trait

d. Disruptive: maintains extreme values in the population

3. Genetic drift

a. Genetic drift​ = Change in gene frequency in a population over time, caused entirely by random​ factors.

b. Sampling error effects: more likely to change the frequency of alleles in a small population

c. Founder effect ​ ​= a component of genetic drift theory, stating that new populations that become isolated from the parent population carry only the genetic variation of the founders.

d. Genetic bottleneck​ = temporary dramatic reduction in size of a population or species

e. Sexual selection​ = differential reproductive success within one sex of any species 4. Gene flow

a. Gene flow​ = Movement of individuals (and their genes) between populations b. Makes populations more similar to one another

c. Counteracts the evolutionary forces that cause populations to diversify 5. Nonrandom mating

a. Inbreeding​ = ​mating between close relatives

i. Raises the frequency of homozygous genotypes at all loci

ii. Decreases the frequency of heterozygous genotypes at all loci

b. Assortative mating

i. Negative AM:​ increases frequency of heterozygous genotypes for

particular loci

ii. Positive AM:​ increases frequency of homozygous genotypes for particular loci

Formation of Species

Microevolution​ = small changes occurring within a species, such as changes in allele frequencies

Macroevolution​ = large changes produced after many generations, such as the appearance of new species.

Biological species concept​ = groups of interbreeding natural populations, which are reproductively isolated from other such groups

● Reproductive isolation

○ Physical barriers (e.g. geographic)

○ Intrinsic barriers (e.g. physiology, behavior)

○ Premating mechanisms 

■ Habitat isolation

■ Temporal isolation

■ Behavioral isolation

■ Mechanical incompatibility

○ Postmating mechanisms 

■ Sperm-egg incompatibility

■ Inviability of the zygote-fetus or offspring

■ Offspring sterility

Ecological Species Concept​ = a group of organisms exploiting a single ecological adaptation. ● Hybrids do worse than the specialized ones (e.g., Darwin’s finches)

Evolutionary Species Concept​ = defines species as evolutionary lineages (ancestral-descendant sequences of populations) with their own unique identity.

Morphological Species Concept​ = defines species based on anatomical similarities. ● Not always reliable because some species can be polymorphic and different species can be very similar

● But sometimes is the only one that can be used (paleontology)

Major Modes of Speciation

● Cladogenesis

● Anagenesis

○ Chronospecies​ ​= each species within an anagentic line

Processes of Speciation:​ different ways in which populations become isolated ● Allopatric​ = speciation occurring via complete geographic isolation (physically separate places)

○ E.g., Continental drift, physical barriers, natural disasters, mountain ranges ○ Divergence: genetic drift, mutation, natural selection

● Parapatric​ = speciation involving only partial geographic isolation

○ Wide geographic range, BUT no​ discrete physical boundaries between that range ○ Easier to mate with individuals close to them

○ Hybrids in the middle zone

○ Divergence: mutation, natural selection, nonrandom mating

● Sympatric​ = speciation occurring in the absence​ of geographic isolation ○ No isolation

○ Less common form of speciation

○ Divergence: mutation, natural selection, mate recognition, selective breeding

Niche​ = how a species “makes a living”, which includes how it interacts with its environment, with other species in its community, and how it utilizes resources in its habitat. ● Species that live together in the same habitat must have different niches in order to avoid being in direct competition with other species.

Gradualism​ = Evolutionary change proceeds gradually through accumulated small-scale changes.

Ch.6: Human Variation

Species → subspecies → populations → individuals

● Humans are phenotypically diverse

● Subjective bias → Human ​genetic​ diversity is surprisingly ​low

○ The human species is relatively recent in evolutionary terms

○ Depending on the locus examined, chimpanzees show 2 to 4x more genetic diversity than humans

○ Possible reasons: 

■ Relatively recent bottleneck event in human evolutionary history

■ Gene flow between different human populations due to migration

Race​ = a group of populations sharing certain characteristics that make them distinct from other groups of populations; often incorporates biological and cultural criteria. ● Some variation is geographically structured

● People tend to choose their mates among those they live close to

● The relationship between geographic and genetic proximity reflects gene flow ● There is more variation within a population than between different continental populations

● 2nd definition:​ Race = a typological and arbitrary concept, which assumes that human variation can be classified into a number of distinct groups

● Clinal distribution​ = patterned distribution across a geographic gradient ○ Skin color

○ ABO blood types

Summary:

● Human variation is poorly described by racial classifications

● More genetic variation is attributed to differences among individuals ​than among populations

● Distribution of many traits that have historically been used to define “racial types” is continuous

● Poor concordance​ among traits

Biology of Skin Color: Dermis and Epidermis

● Keratinocytes​ = produce keratin​, which affords protection against water and abrasion ● Melanocytes​ = produce the pigment melanin​.

The color of your skin depends on:

● Hemoglobin

● Keratin

● Melanin

○ Number of melanocytes is approximately the same in all individuals, but the amount of melanin deposited in keratinocytes varies​.

○ Dark skin: synthesis of large amounts of melanin

○ Light skin: synthesis of less melanin

● Electromagnetic spectrum

○ Ultraviolet radiation =

○ Intensity of UV is greatest at the equator and decreases towards the poles ○ Melanin blocks the UV portion of sunlight from penetrating through the skin ○ The degree to which UV penetrates the skin is inversely proportional to the amount of melanin in the skin

3 Main Theories: 

1. Skin damage and skin cancer

2. Nutrient photolysis: Folic Acid

3. Vitamin D synthesis

Sunburn

● Facilitates infection, impairs thermoregulation, permanent damage

Skin Cancer

● Skin cancer by damaging DNA

● Highest incidence of skin cancer in light-skinned people, particularly those in tropical zones

● Selection for dark skin at the equator, where UV is high

Nutrient Photolysis:

● Chemicals essential for metabolism are sensitive to excess UV radiation and will undergo decomposition (photolysis)

● Folic Acid:

○ Important for central nervous system development; DNA replication and cell division

○ Deficiencies can lead to pregnancy complications, defects, impaired sperm production → negative reproductive success

○ Selection for dark skin at the equator, where UV is high

Vitamin D synthesis:

● Essential for calcium metabolism, and normal bone and tooth development ● Difficult to obtain from diet

● Primary source of vitamin D is synthesis within the skin

● Dark skin requires six times as long to make the same amount of Vitamin D as light skin ● Effects of underexposure to UV​:

○ Rickets​ = a disease affecting children, caused by vitamin D deficiency. REsults in impaired mineralization of developing bones and teeth

○ Negatively impact reproductive success, and drive selection for lighter skin color in areas with reduced UV exposure.

○ Result: ​clinal distribution or gradient

Other human traits shaped by natural selection:

● Sickle cell anemia 

○ Genetic disorder resulting from single point mutation in hemoglobin gene ○ Sickle blood cells pile up, inability to carry oxygen to other muscle cells ○ Genotypes:

■ HbA HbA (homozygous normal)

■ HbS HbS (homozygous sickle cell variant)

■ HbA HbS (heterozygous - incomplete dominance, SC trait - some sickling occurs in low oxygen situations)

○ Why doesn’t natural selection remove the sickle cell allele?

■ Advantage: Heterozygous​ genotypes protects against​ malaria, selective advantage in areas with malaria in comparison with the other two

genotypes

● HbA HbS carriers have natural resistance to malaria

■ Heterozygote advantage​ = selection against both alleles in the

homozygous condition, and a selective advantage of the heterozygous

condition

■ Balanced polymorphism ​= stable polymorphism, occurence of two or more different phenotypes

● Lactose intolerance 

○ All mammals drink milk in infancy

○ Lactase enzyme breaks up lactose (glucose + galactose) into constituent parts ○ Most mammals lose the ability to produce lactase after weaning

○ Genetics:

■ LCT*P (dominant) = lactase persistence

■ LCT*R (recessive) = lactose intolerance

○ Lactose tolerance evolved by recent natural selection favoring lactase persistent individuals in cultures that rely on dairy products

○ Adult lactase persistence

■ Caused by mutation, results in permanent production of lactase enzyme ■ Neutral in cultures with no dairying tradition

■ Beneficial in cultures with dairying tradition

● Body size and shape 

● Bergman’s Rule​ = individuals living in colder habitats tend to have larger body sizes: less heat lost through body surface

● Allen’s Rule​ = extremities tend to be longer relative to body size in warmer climates to dissipate heat

● Oxygen availability at altitude

○ Air is less dense, so fewer molecules of oxygen in same volume of air ○ Altitude sickness

○ Adaptations to high altitudes: Andeans (increase in hemoglobin and lung size) and Tibetans (lower hemoglobin, increase in respiratory rate and blood flow) Summary

● Traditional racial groups do a poor job of explaining human diversity ● Human diversity is geographically structured (clinally distributed)

● Many traits are shaped by natural selection

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