ANTH 1200 Topic 11 Human Variation Notes PDF

***Topic 11:*** **Human Variation** **Overview** - - - **Introduction** - - I.e., we are concerned with the ways in which human populations physically resemble or differ from each other and why - - External features include skin/hair colour, height, proportions of limbs,...

***Topic 11:*** **Human Variation** **Overview** - - - **Introduction** - - I.e., we are concerned with the ways in which human populations physically resemble or differ from each other and why - - External features include skin/hair colour, height, proportions of limbs, etc. - Internal features include blood type, susceptibility to disease, etc. - - - - They may be the product of relatively minor **genetic differences** (i.e., nature) - Conversely, they may be the product of growing up in a particular **physical and/or cultural environment** (i.e., nurture) - Alternatively, they may be produced by an **interaction** between genetic and environmental factors - **[Processes in Human Variation ]** **Natural Selection** - - - - - **Natural Selection & Humans** - - **Directional Selection** - - - - - - - **Normalizing Selection** - - - - E.g., salmon - - **Balancing Selection** - - - - **Neutral Traits** - - - **Influence of the Physical Environment** - - - - - - **Influence of the Cultural Environment** - - - - cooking food "relaxes" the natural selection for physical traits associated with heavy chewing - wearing clothing and living in heated houses reduce the need for our bodies to completely adapt to cold environments - - **Review Questions** - What are some human traits that might be selected for under different environmental conditions? - What are the differences between a) directional selection, b) normalizing selection, and c) balancing selection? What are some examples of each type of natural selection? - What are neutral traits? What are some factors that might account for different frequencies of neutral traits in different populations? - How can physical environment affect the growth and development at the human body? - What is acclimatization? How is it different from adaptation? - What are some of the cultural factors/practices that could potentially affect human growth and development? **[Biological Diversity in Human Populations ]** **Human Biological Diversity** - - - learned behaviours - (relatively minor) traits specific to individual populations - changes to the entire species - - **Body Build and Facial Construction** - - - **Bergmann's Rule** - - - - - - - - - **Humans & Bergmann's Rule** - - - **Exceptions to the Rule** - Some human populations appear to be **exceptions** to Bergmann's rule, however - E.g., short, compact pygmies are found only in tropical rainforests in Africa - - **Allen's Rule** - - - **Humans & Allen's Rule** - - - - **Combining Bergmann's & Allen's Rules** - - **Genes, or Environmental Effects?** - - - **Facial Structure & Climate** - - - **Climate & Human Faces** - - - - - **Skin Colour** - - - - For example, populations characterized by extremely dark skin in both Africa and southern India are not closely related either genetically or historically; populations in southern India are more closely related to other non-African populations (including Europeans) than they are to exclusively African populations - **Factors Contributing to Skin Colour** - 1. amount of **melanin**, the dark pigment, in the skin 2. amount of blood in the small blood vessels of the skin **Gloger's Rule** - - - **Advantage of Dark-Coloured Skin** - - - - - - - - **Advantages of Light-Coloured Skin** - - - - - - - **Adaptation to High Altitude** - - Air pressure at 3000 meters is 60-70 percent of sea level - - - **Hypoxia:** a condition of oxygen deficiency that often occurs at high altitudes (p. 123) - - - Interestingly, their caloric expenditure is also typically less (2094 kcal/day for an adult male, compared to 2,500 kcal/day for typical western male) **Andean Adaptations: Nature or Nurture?** - - - - **Genetic Potential for Adaptation?** - - - - E.g., low and high altitude dwellers in the Himalayas do not differ in chest or lung size **Height** - - **Height and Climate** - - - - - **Height, Nutrition & Disease** - - - - - E.g., in Germany during World War II the stature of children 7 to 17 years of age declined, despite the general trend towards increasing stature - - - **Worldwide Increases in Stature** - - - - - - - **Susceptibility to Diseases** - - - **Virgin Soil Epidemics** - - - - COVID-19 coronavirus and other modern diseases (e.g., SARS, H1N1, West Nile virus, bird flu, Ebola) - 1918 flu pandemic - Various diseases introduced into the New World by Europeans - Black Plague (14^th^ century AD) **Susceptibility & Genetic Homogeneity** - - - - - - **Culture and Disease** - - - - - they provide **concentrated populations** in which diseases can maintain themselves - **poor sanitary conditions** - close proximity of humans and domesticated animals facilitates the transmission of diseases between species **Sickle-Cell Anemia** - - - - - - - **Why Hb^S^ Remains in the Gene Pool** - - - **Review Questions** - What is Bergmann's Rule? What are some examples of human populations that appear to demonstrate this rule? Why do some populations appear to defy this rule? - What is Allen's Rule? What are some examples of human populations that appear to demonstrate this rule? Why do some populations appear to defy this rule? - Can the differences between populations that are explained using Bergmann's and Allen's rule always be attributed to genetic differences between these populations? Why or why not? - What are some of the ways in which facial structure may represent adaptations to climatic conditions? - Is skin colour invariably an accurate indicator of ancestry? - Beyond genetics, what are the two physical factors that determine skin colour? - What is Gloger's Rule? - What are some of the advantages of dark coloured skin in sunny climates? Which of these advantages is more easily explained via natural selection? Why? - Why might light skin colour be selected for in a temperate climate? Why might women typically have lighter skin than men in the same population? - What is hypoxia? How have populations in the Andes adapted to conditions that might produce hypoxia? - What are some of the environmental factors that might affect the average height of a given population? Can cultural factors ever be used to explain differences in average height in different populations? - What is a secular trend? - What is a virgin soil epidemic? Give some examples. Why is a more genetically homogenous population potentially at greater risk from infectious disease than a more genetically diverse population? How can the spread of disease be affected by cultural factors? - Why has the allele responsible for sickle cell anemia probably remained in the gene pool in parts of the world significantly affected by malaria? **[Race and Racism ]** **The Biological Fallacy of Race** - - - - - **Race as a Social Construct** - - **Why Invent Social Categories?** - - - - **Manipulating Racial Classifications** - - - - - - - - - - - - **\ ** ::: {.section.footnotes} ------------------------------------------------------------------------ 1. ::: {#fn1} NOTE: unless otherwise indicated, most key definitions with page numbers in the notes for this course derive from Ember, Carol R.; Melvin Ember; Peter N. Peregrine; Robert D. Hoppa and Kent D. Fowler. 2018. *Physical Anthropology and Archaeology (4th Canadian Edition).* Pearson.[↩](#fnref1){.footnote-back} ::: :::