HUMAN POPULATIONS and VARIATION

Read Chapter 14

 

 

Human Racial Groups

Linnaeus' Systema  Naturae

Classification of Humanity, 5 types

1) Wild

2) Copper (American)

3) Fair (European)

4) Sooty (Asian)

5) Black (African)

 

Biological definition: Large group of people who resemble each other due to common, shared genes.

Sociological definition: Large group of people who share a common language, religion, and culture.

 

Geographic Races: Grouping populations together based on location and proximity, as well as on physical similarities.

 

Common Race Assumptions:

·        Humans can be divided into specific types.

·        Race predicts a group's moral and mental capacities.

·        Race predicts an individual's ability.

 

IQ, Intelligence, and Race

Henry Goddard (1866-1957)

1) Coined the term "moron": High-grade defective; intellectually dull, socially inadequate, and morally deficient.

2) The Kallikak Family: A Study in the Heredity of Feeble-mindedness (1912).

·        Martin Kallikak: Married to a "worthy" Quaker woman; Also "dallied" with a feeble-minded tavern girl.

·        2 decent lines: One of worth and one of morons.

·        Goddard proposed there was a single dominant gene for feeble-mindedness which was passed down from the tavern girl.

3) Link between genes and intelligence (though not racial, in this case).

4) Goddard suggested the sterilization of those with the gene for feeble-mindedness.

 

E.A. Hooten (1920): Used "non-adaptive" traits as indicators of race.

 

Traits traditionally used to distinguish race are now known to be polygenic and adaptive.

 

Skin Color

·        Depiliation: Reduction of body hair.

·        Pigmentation related to latitude.

·        Gloger's Rule: Skin pigmentation decreases with increasing distance from the equator.

·        Dark skin protects against UV radiation.

1) skin cancer

2) folate destruction

·        Light skin encougages vitamin D synthesis at latitudes with reduced UV exposure.

1) rickets

 

Hair color and texture related to skin pigmentation.

 

Eye shape characteristics may be related to protecting the eyes from dust, or cool, dry air.

 

Nose size and shape may be related to climate.

·         A longer, larger nose may warm and moisten cool, dry air. 

 

Body type and size are due to climate and nutrition.

·         Bergmann & Allen Rules

·         Secular trend

 

1) Race as traditionally recognized is not a biological entity.

2) Variation within a race is greater than the variation between different races.

3) Human species relatively homogeneous when compared to other species (chimpanzees, for example). 

4) Racial groupings typological, but human populations do not fit well into discrete types, particularly if more than just a few traits are examined. 

 

Population Genetics

Anthropologists have moved away from describing human populations in typological terms, and now focus on relationships between various populations.

 

1) Analysis of genes can indicate the level of genetic relatedness between populations. 

2) Populations may carry genes specific to themselves (genetic markers).

3) Genetic Differences (or distance) between populations gives an idea as to relatedness or past relationships. 

4) Genetic distance methods can be used to construct phylogenetic trees of modern human populations.

5) Based on gene frequencies.

·        Mitochondrial DNA (mtDNA) Analysis: Mitochondria in cells carry their own DNA; it is inherited through one’s mother. 

·        Chromosomal/Nuclear DNA: Carry human genes; many more genes than mtDNA

 

Evidence suggests that modern humans developed in Africa.

1) African populations show the most within-group variation.

·        Longest period for the development of differences.

 

African populations moved first into southern Asia; southern Asian populations then moved into north Asia and south to Oceania.

1) Early split between African and Asian populations.

 

Europeans show little within group variation.

·        Either evolved more slowly or experienced recent gene flow from Africa and Asia.

 

Native American populations descended from NE Asian (Siberian) populations.

·        Genes suggest anywhere from 20 – 40 thousand years ago.

·        May have been more than one migratory event.

 

Recent Population Movements:

1) Expansion of North African and Middle Eastern populations ~4,000 years ago.

2) Invasion of Central Asian pastoralists.

3) Pacific Islands settlement from Southeast Asia less than 4,000 years ago.

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