Race & Human biology

OutlinePrinciples of evolution over next two weeks. Examining modern human diversity as baseline for discussion of evolutionary trajectory.

Two Approaches to raceHuman Variation & Skin Color & Natural SelectionGenetic Inheritance & Ancestry Informative Markers

Before we start, remember

Concept of race does not explain human evolution

Racial categories not fixed, no attached innate characteristics, abilities, or inclinations

Biological correlations with cultural achievements is dangerous & misguided

Race: Discredited concept in biology

Two Anthropological Approaches1) Racial Classification 2) Explanatory Approach

Racial classification: traditional approach attempts to assign individuals to discrete categories purportedly based on common ancestry

Assumed that biological characteristics were determined by heredity & stable (immutable) over time

Racial Classification is wrongGroups do vary biologically in some genetic attributesBut change= gradual shifts in genetic frequency --- clines

Clines incompatible with discrete categories

Race is supposed to reflect shared genetic material but instead has been based on phentotype (huge difference)

Racial ClassificationRacial classification based on phenotype is difficult & subjective

Lack suite of accurate traits to group people. Diverse eyes, hairs, skin, etc.

Phenotype does not necessarily have a genetic basis-short term (tanning) & long-term (environmental conditions)

Human populations not isolated long enough for true group isolation (gene flow)

Explanatory approach

Explanatory approach: Attempts to explain differences & similarities, rather than classify into false discrete groups

Natural selection: process by which forms most fit to survive & reproduce in a given environment do so in greater numbers than others in same population

Mutation & InheritanceInheritance is messy; not 1:1Bill and Luke Waltonhttp://youtu.be/FxosAsUczFINatural Selection is not linear or progressiveGenetic mutation is your friend

Explanatory Approach Continues

Black UhuruThe whole world is Africa

Human demographic history indicates that pure human stocks do not exist (unless you count Africa)

No population is more highly evolved than any other population

Unilineal evolution: A pattern of cultural progress through a sequence of evolutionary stages

What about skin color?

That has evolved right?

Human variation is distributed clinally across the globe: Geographical distribution of skin pigmentation

Skin color is a phenotypic characterPhenotype: the observable physiological & anatomical traits

Phenotype often used to classify individuals to a particular race

Phenotypes= highly plastic & influenced by the environment

Simplistic & stereotypical to equate skin color w/ race.

Still, it is most noticeable aspect of appearance (you vs. others)

Skin color

Melanin primary determinant of human skin color, chemical substance produced in epidermis

Melanin index measures amount of melanin present in skin or hair

Melanin indices do not support static categories

Possible Selection Pressures for Darker SkinProtection from sunburnProtection from skin cancerProtection from photolysis of folic acidProtection from immune system suppression

Possible Selection Pressures lighter skinEnhanced vitamin D synthesis

Enhanced immune suppression Protection from cold damage

Light skin protects from Rickets

Dark skin protects from Hypervitaminosis: too much vitamin d calcium deposits build up in soft tissuesLess sunlight would also lessen selection pressures for dark skin

Lactose intolerance

Phenotypic adaptation: adaptive changes occur during an individuals lifetime

Adult milk consumption is unnaturalWho is lactose intolerant?

Northern Europeans, Tutsi (Rwanda) , Burundi (East Africa) (herders) love the milk

People can increase lactose tolerance with more intake, probably a combination of genes & phenotypic adaptation

Brief Paws

Partitioning Human DiversityRichard Lewontin, 1972Looked at serum proteins & red blood cell enzymes in a global population panel

85.4% of diversity is contained within populations.

Less than 15% of human diversity accounts for the differences observable between populations

AllelesGenes contain information about a specific characteristic or trait & can either be dominant or recessive.

Not all copies of a gene are identical & alternative forms of a gene, called alleles, lead to the alternative form of a trait.

Genes (alleles) mutate, are selected for differentially, & not passed on 1:1 (messy)

About 5% of the genetic variation not shared between populations is informative about ancestry. These alleles can be called Ancestry Informative Markers (AIMs).

What is ancestry?Genealogical ancestry - the expected level of ancestry based the origins of ones relatives (~qualitative)Country of origin, ethnicity

Genomic ancestry - the realized ancestry as estimated with data such as AIMs

So which is the TRUE ancestry?

BOTH. Depends on the question.

BioGeographicalAncestry (BGA) using Ancestry Informative Markers for three parental populations:West African,Native American,European (n=30 for each population)

Black Drugshttp://www.bidil.com/pnt/http://youtu.be/-2Q8gwvTees

What do AIMS look like?

Is race biologically meaningful?NORace is a cultural construct

Racial categories vary cross-culturally

No universal human racial classification exists

There is no test that determines blackness or Asianess

Analysis of AIMS (alleles) & skin pigmentation has little to do with how we culturally identify ourselves.

If it did, we would have very different groups of people.

Race as a cultural construct

Race is a cultural construct but it is still very real.

It is real because we deal with it every single day.

Problems with thinking of race as simply a cultural construct (Thompson 2006)[A]ll ideas beyond the idiosyncratic are social constructs insofar as they are shared cultural knowledge.

Better argument= Race is social construct that is poorly descriptive of the phenomenon it seeks to describe and has a long history of devastating consequences for individuals

Racist Thinking A race is defined as a groupof individuals sharing commongenetic attributes which determine that group'sphysical appearance and,more controversially, theirCognitive abilities.---From www.stormfront.org

What is wrong with this statement?

Race and IntelligenceRace has no biological basis

No biological rules for determining group membership. Race is self-reported.

Various genes (and even skin color) would have us lumped into different groups.

Low test scores on aptitude tests has everything to do with socioeconomic status (access to resources like schools, teachers, etc.) and cultural knowledge.

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