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Chapter 15

Chapter 15. Modern Human Biology: Patterns of Adaptation. Chapter Outline. The Adaptive Significance of Human Variation Infectious Disease. Adaptive Significance of Human Variation. Human variation is the result of adaptations to environmental conditions.

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Chapter 15

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  1. Chapter 15 Modern Human Biology: Patterns of Adaptation

  2. Chapter Outline • The Adaptive Significance of Human Variation • Infectious Disease

  3. Adaptive Significance of Human Variation • Human variation is the result of adaptations to environmental conditions. • Physiological response to the environment operates at two levels: • Long-term (genetic) evolutionary changes characterize all individuals within a population or species. • Short-term, temporary physiological response is called acclimatization.

  4. Pigmentation and Geographical Divisions • Before 1500, skin color in populations followed a geographical distribution, particularly in the Old World. • Populations with the greatest amount of pigmentation are found in the tropics. • Populations with lighter skin color are associated with more northern latitudes.

  5. Distribution of Skin Color Among Indigenous Populations

  6. Skin Color Influenced by three substances: • Hemoglobin, when it is carrying oxygen, gives a reddish tinge to the skin. • Carotene,a plant pigment which the body synthesizes into vitamin A, provides a yellowish cast. • Melanin,has the ability to absorb ultraviolet radiation preventing damage to DNA.

  7. Production of Vitamin D

  8. Thermal Environment • Mammals and birds have evolved complex physiological mechanisms to maintain a constant body temperature. • Humans are found in a wide variety of thermal environments, ranging from 120° F to -60° F.

  9. Human Response to Heat • Long-term adaptations to heat evolved in our ancestors: • Sweat Glands • Vasodilation • Bergmann's rule - body size tends to be greater in populations that live in cold environments.

  10. Human Response to Cold • Short-term responses to cold: • Metabolic rate and shivering • Narrowing of blood vessels to reduce blood flow from the skin, vasoconstriction. • Increases in metabolic rate to release energy in the form of heat.

  11. High Altitude • Multiple factors produce stress on the human body at higher altitudes: • Hypoxia (reduced available oxygen) • Intense solar radiation • Cold • Low humidity • Wind (which amplifies cold stress)

  12. Infectious Disease • Caused by invading organisms such as bacteria, viruses, or fungi. • Throughout evolution, disease has exerted selective pressures on human populations. • Disease influences the frequency of certain alleles that affect the immune response.

  13. Small Pox • The only disease considered to be eliminated as a result of medical technology • Smallpox has a higher incidence in those with type A or AB than in those type O blood. • The immune systems of individuals with type A antigen may not recognize the small pox antigen as a threat.

  14. Impact of Infectious Disease • Before the 20th century, infectious disease was the number one limiting factor to human populations. • Since the 1940s, the use of antibiotics has reduced mortality resulting from infectious disease.

  15. Impact of Infectious Disease • In the late 1960s, the surgeon general declared the war against infectious disease won. • Between 1980 and 1992 deaths from infectious disease increased by 58%. • Increases in the prevalence of infectious disease may be due to overuse of antibiotics.

  16. Zoonoses and Human Infectious Disease

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