Anthropology Chapter 14 (Modern Human Variation)

What is Race?

- a modern idea -no genetic base -human subspecies -human subspecies do not exist -skin color is one of thousands of differences between any given human -most genetic variation is found within groups classified as "races"

Biological Determinism

-Cultural and biological variations are inherited (e.g. intelligence, morals, values are inherited like biological traits) Note: Post 1850, a constant underlying theme in common and scientific thinking

Races and Polygenic traits

-Races are typically defined using polygenic traits, influenced by more than one gene and exhibiting a continuous range of expression -the difficulty is in drawing distinct boundaries between populations

What else about Race?

-Slavery predates race -American ideas of freedom evolved with ideas concerning race -accepting "race" justifies social inequalities -"Race" may not be a biological category, but racism is still real -colorblindness will not end racism

"Race" as Term

-The term race has been used to refer to culturally defined groups since the 1600s -It has been used synonymously with species, e.g. "the human race" -it is used as a biological term that carries enormous social significance

Polymorphisms at the DNA level

-copy number variants (CNV) are repeated DNA segments, either a few or hundreds of time -segments vary, defining "DNA" fingerprint -single-nucleotide polymorphisms (SNP) throughout the human genome are extraordinarily variable

What we are able to understand now...

-high degree of genetic variation in African populations -nature of human migrations out of Africa -evidence of the role genetic drift has had in recent evolution -patterns of human variation at global level to identify genetic risk factors

Population Genetics & Race

-humans differ individually within populations far more than large geographical groups differ from one another -geographically patterned genetic clusters are not "races"; are not linked to simple patterns of phenotypic variation -correlations are broad, so not all individuals can be easily classified

Factors that Act to Change Allele frequencies & cause contemporary evolution in humans

-new variation (mutation) -redistributed variation (gene flow or genetic drift) -selection of "advantageous" allele combinations that promote reproductive success (natural selection)

What are the hypothetical conditions that a Hardy-Weinburg Equilibrium population would be assumed to meet?

-the population is infinitely large to eliminate the possibility of random genetic drift or changes in allele frequencies due to chance -no mutation -no gene flow -no natural selection -mating is random

Understanding Human Variation: Ethnicity

A group of people that share common cultural origins, language, history, and cultural traits Note: Terms like ethnicity or population more accurately describe differing groups of humans than race

How do you know if a trait is polymorphic?

A trait is polymorphic if the locus that governs it has two or more alleles

Understanding Human Variation Race:

Biological classifications within a species based upon variation among external and observable (phenotypic) traits

Human Bicultural Evolution

Ex: Lactose Intolerance -in a ll human populations children are able to digest milk -in most mammals, including humans, the gene that codes for lactase production "switches off" in adolescence -the geographical distribution of lactose tolerance is related to a history of cultural dependence on fresh milk products

Biological Determinism: Eugenics

Francis Galton (Darwin's cousin) "race improvement" through forced sterilization and encouraged reproduction

Nonrandom Mating:

Incest avoidance

Why are polymorphisms used?

Polymorphisms are used to understand evolutionary processes in modern populations

What does population genetics focus on?

Population genetics focuses on variable DNA polymorphisms

What does population genetics provide?

Population genetics provides more accurate measures of within-group and between-group variation Note: We can study very recent events in human population history & microevolution

What are racial categories?

Racial categories are invalid, biological anthropologists study differences in physical traits

What is the Gene Pool?

The total complement of genes shared by the reproductive members of a population

Historical Views of Human Variation

To account for physical differences: -ancient egyptians classified based on skin color -linnaeus classified four categories with behavioral and intellectual qualities -Blumenbach (1752-1849) classified five races based on more than skin color

True or False: Genes are mixed and rejoined every generation

True Note: The next generation is the direct result of genes going into the pool (who is mating with whom)

What is lactose intolerance?

an individual's inability to digest milk among some African and Asian populations

Racism

based on the false belief that intellect and cultural factors are inherited with physical characteristics -uses culturally defined variables to typify all members of particular populations -assumes that one's own group is superior -racism is cultural

What does the Hardy-Weinberg Equilibrium do?

establishes a set of conditions in a population where no evolution occurs

What creates Breeding isolates?

geographic, ecological, and social factors affect mate choice

Nonrandom Mating: Assortive Mating

individuals mate more often than expected by Hardy-Weinberg predictions

What information do racial categories yield?

population adaption genetic drift mutation gene flow

What are Breeding isolates?

populations, isolated geographically and/or socially from other breeding groups Note: -influenced by cultural rules -marrying/mating within group, or endogamy -marrying/mating outside group, or exogamy

Nonrandom Mating: Inbreeding

relatives mate more often than expected, reducing genetic variability, potentially reducing reproductive success

What are polymorphisms?

traits that differ in expression between populations and individuals

Nonrandom Mating

with mate choice based on social status, ethnicity, biological relationship, etc.