Week 13: modern human variation

Week 13: Modern Human Variation

Differences in Human Variation

  • Human variation can be categorized into several domains:

    1. Biology

    2. Physiology

    3. Chemistry

    4. Behavior

    5. Culture

  • Figure 13.1: Humans show cultural diversity which contributes to a great degree of variation between individuals. However, genetically, the shown individuals are relatively undiverse.

    • Examples of culturally diverse groups:

    • Top left: Hadzabe members in Tanzania

    • Top right: Inuit family

    • Bottom left: Andean man in Peru

    • Bottom right: English woman

The Concept of Race During the Scientific Revolution

  • The concept of “race” began to take shape during the Renaissance period (~14th century).

    • It was associated with sea travel, where long-distance voyages resulted in encounters with people who were culturally and physically distinct.

    • Writings from early explorers reveal an “us vs. them” mentality, highlighting perceived differences.

Historical Development of the Race Concept

  • 1758: Carolus Linnaeus created a biological classification system for humans, grouping them with apes and monkeys.

    • Identified five subspecies or races of humans:

    • Homo sapiens afer: Africans

    • Homo sapiens americanus: American Indians

    • Homo sapiens asiaticus: Asians

    • Homo sapiens europeaus: Europeans

    • Homo sapiens ferus: Wild men

    • This was the first attempt at classifying humans into races.

  • 1775: Johann Friedrich Blumenbach developed the first “scientific” racial taxonomy.

    • His taxonomy was mainly based on skull morphology.

    • Concluded that five static racial categories existed:

    • Ethiopian/African

    • Mongoloid

    • Caucasoid

    • American Indian

    • Malay

Debunking the Race Concept

  • Franz Boas was a significant figure in challenging the taxonomy of human variation.

    • In the early 1900s, he researched the skull shapes of immigrant families and discovered no support for distinct racial types.

    • Concluded that the race concept was invalid.

    • Despite this, the anthropological study of race continued until the 1960s due to persistent cultural biases.

Race and Genetics

  • Individual humans demonstrate significant similarity to one another:

    • Genetic difference between individual humans is approximately 0.1%.

    • In contrast, the genetic difference among individual chimpanzees is about 1.2%.

  • When assessing human variation, it is crucial to focus on populations, not individuals.

    • Most human genetic information is found within populations rather than between them.

    • There is roughly a 5-10% genetic difference between human populations.

Genetic Variation Across Human Populations

  • Genetic variation between populations from Central America, Asia, and Africa is approximately 10%.

  • Comparatively, genetic variation among white-tailed deer populations from North Carolina and Florida is about 70%.

Genetic Testing and Racial Group Variation

  • Richard C. Lewontin was one of the first to conduct genetic tests in the 1970s.

    • Analyzed blood groups, serum proteins, and red blood cell enzymes across different “racial” groups.

    • Found that there was greater variation within each traditional “race” than between them.

    • DNA patterns do not support the existence of distinct races among humans.

Morphological Studies and Human Variation

  • Studies on human morphology (e.g., height, body mass index, cranial shape) have also indicated that there is more variation within human populations than between them.

  • Human body variation is influenced by factors such as gene flow, mating patterns, nutrition, and health.

  • There is no support for the notion of biological races.

The Social Implications of Race

  • While the concept of race may lack biological meaning, it remains significant as a social concept.

  • The social understanding of race has continued to impact areas such as health and various aspects of life.

Evolutionary Similarities

  • The observed genetic similarity among humans is tied to our evolutionary history.

    • Humans are a recent species, with more genetic variation existing among populations in Africa than among all populations outside of it.

    • Continuous gene flow throughout human evolutionary history has influenced this similarity.

  • Human populations are noted for their mobility and tendency to interbreed, leading to an increase in similarity between populations but greater diversity within them.

    • Variations are observed in populations outside of Africa (e.g., Asian and European populations) compared to the substantial variation within African populations.

Human Variation and Clines

  • A cline is defined as a distribution of trait variations that show continuous gradation across geographical areas.

    • Examples include:

    • ABO Blood Types

    • Skin Color

  • The distribution of human skin color is clinal, ranging from lightest to darkest.

ABO Blood Group System and Neutral Processes

  • The clinal distribution of the ABO blood group system is influenced by neutral microevolutionary processes such as:

    • Gene flow: People tend to interbreed and exchange genetic material with nearby populations.

    • The blood type B allele shows an east-to-west cline across Eurasia.

  • In South America, approximately 90-100% of the native population carries the recessive blood type O allele.

  • Genetic Drift (specifically, the Founder's effect): Occurs when a small population migrates to a new area, resulting in genetic changes.

  • Graphical Representation of blood type distribution:

    • Percent of Population with B Allele:

    • 0-5%

    • 15-20%

    • 5-10%

    • 10-15%

    • 20-25%

    • 25-30%

    • Percent of Population with O Blood Type:

    • 50-60%

    • 70-80%

    • 60-70%

    • 80-90%

    • 90-100%