Modern Human Physical Variation and the Concept of Race

Exam Preparation and Expectations

• Timeliness and Materials
  • Arrive on time for the exam.
  • Bring a pencil.
• Accommodation
  • Students with letters of accommodation can meet at $8:30$ AM in BSB $2110$ OR make arrangements to take the test in the testing center.
• Study Resources
  • The PowerPoints are the primary study guide.
  • All exam questions will be based on information presented in the PowerPoints and/or in class discussions.
• TA Communication Before Test
  • Do not write to TAs the night before the test asking what will be on it.
  • TAs will not be answering questions during the weekend prior to the test.
• Example Question
  • Question: "Recently, evidence of a uniquely small type of human was found on a small island in Indonesia. They have been named __."
  • Answer: Homo floresiensis.
    • Key Characteristics of Homo floresiensis:
      • Height: $106$ cm
      • Weight: $28$ kg
      • Brain: $426$ cm$^3$
    • Comparison to other Hominins:
      • Homo habilis:
        • Height: $118$ cm
        • Weight: $33$ kg
        • Brain: $614$ cm$^3$
      • Homo erectus:
        • Height: $165$ cm
        • Weight: $51$ kg
        • Brain: $860$ cm$^3$

Hominin Evolution and "Out of Africa" Theory

• Complexity of Human Evolution
  • Twenty years ago, human evolution was known to be complicated, but the extent of future discoveries was unknown.
  • The past was a much more crowded place, with more hominin species than previously thought.
• Model of Hominine Evolution (Simplified Tree)
  • The model illustrates various hominin species and their relationships, with many "dead ends" (extinct lineages).
  • Key species mentioned include: A. anamensis, A. afarensis, A. africanus, A. ardipithecus, A. robustus, A. boisei, H. habilis, H. erectus, Neanderthal, Denisovans, H. floresiensis, and H. sapiens.
  • "Mitochondrial Eve" is placed around $2.0$ million years ago on the diagram, but later text clarifies the genetic evidence points to a more recent $200,000$ years ago.
• Recent Discoveries and the "Out of Africa" Model
  • Recent DNA research suggests that most of our genes can be traced to a "new" group of humans who left Africa.
  • These Anatomically Modern Humans (AMH) replaced other existing human groups (e.g., Neanderthals, Denisovans) across the Old World.
  • There is some evidence of mixing between AMH and these other groups.
• Timeline of AMH Spread
  • The spread of AMH occurred in the last $200,000$ years.
  • The migration beyond Africa perhaps only in the last $100,000$ years.
  • After replacing earlier human forms, AMH continued to occupy new regions globally.
• Evidence for African Origin: The Molecular Clock
  • We do not have the physical remains of our oldest shared ancestor.
  • DNA evidence (Molecular Clock) is used to estimate when our common ancestor lived.
  • Principle: The molecular clock assumes that mutations occur at a relatively constant rate.
  • By looking at differences in mitochondrial DNA (mtDNA, passed through females) in modern populations and calculating the time needed for these variations to develop, the answer is approximately $200,000$ years.
  • This suggests that many of our physical differences have developed in the past $200,000$ years.
• Why Africa? (Principle of Genetic Diversity)
  • In evolution, time equals change, and change equals diversity.
  • According to Yu, et al. (2002), because modern humans originated in Africa, the greatest genetic diversity is found within African populations.
  • Genetic diversity in non-African populations represents a subset of the diversity found in Africa.

Modern Human Physical Variation: Climate as a Driver

• Primary Factors
  • Much of modern human variation is linked to climatic factors, particularly temperature and sunlight.
  • These forces of evolution have been acting on human populations over the past $200,000$ years.
  • Key variations influenced by climate include skin color and body build.
• **Initial Classification and