Chapter Study Outline
1. Is Race a Valid, Biologically Meaningful Concept?
a. Brief History of the Race Concept
i. Race is the classification of human variation.
ii. Early written records do not use the idea.
iii. Some argue the race concept started during the Renaissance.
iv. Other early race concepts began in the eighteenth century.
(1) Blumenbach’s study of skulls in 1775 set a racial taxonomy.
b. Debunking the Race Concept: Franz Boas Shows that Human Biology Is Not Static
i. Franz Boas was among the first to challenge the taxonomy of human variation.
ii. Boas examined the cephalic index and found no support of racial types.
iii. This work was the foundation for a focus on biological process rather than on typology.
c. So-Called Racial Traits Are Not Concordant
i. Robert Lewontin studied global genetic variation.
ii. Racial groups accounted for only 5–10% of variation.
iii. Most variation is among groups, not within groups.
iv. Since Lewontin’s research, a number of other genetic studies have reached the same conclusion.
d. Human Variation: Geographic Cline, Not Racial Categories
i. Specific biological traits follow a geographical gradient (cline).
ii. Skin pigmentation is an example.
2. Life History: Growth and Development
a. The Growth Cycle: Conception through Adulthood
i. Divided into three stages: prenatal (ending with birth), postnatal (to around twelve years of age), and adult (through senescence)
b. Prenatal Stage: Sensitive to Environmental Stress, Predictive of Adult Health
i. Pregnancy lasts nine months.
ii. Involves rapid growth and development, especially of the brain
iii. Prebirth stressors can influence diseases a person may develop later in life.
c. Postnatal Stage: The Maturing Brain, Preparing for Adulthood
i. Divided into five periods characterized by different growth velocities
ii. Development of brain, dentition, motor and cognitive skills, sexual dimorphism, skeletal structure
iii. Environmental effects during childhood influence growth and development.
(1) Secular trends in height; changes in stature caused by Environment
iv. Before adulthood, height deficits caused by growth disruption can be recovered through a period of rapid growth.
d. Adult Stage: Aging and Senescence
i. Aging refers to social, cultural, biological events that occur over a lifetime.
ii. Senescence is a reduction of the body’s ability to respond to stress (homeostasis).
iii. Cessation of reproduction in women is called menopause.
e. Evolution of Human Life History: Food, Sex, and Strategies for Survival and Reproduction
i. Survival and adaptive success are due to food acquisition and reproduction.
ii. Humans are influenced by culture.
iii. Life history develops with human culture.
iv. Prolonged Childhood: Fat-Bodied Moms and Their Big-Brained Babies
(1) Humans have a prolonged childhood with high maternal investment
f. Grandmothering: Part of Human Adaptive Success
i. Postreproductive survival is high with humans.
ii. Women play a large role in caring for children’s children.
3. Adaptation: Meeting the Challenges of Living
a. Adaptation to the environment occurs at four levels.
iii. Physiological (acclimatization)
iv. Behavioral (culture)
b. Climate Adaptation: Living on the Margins
i. Heat Stress and Thermoregulation
(1) Body attempts to maintain core body temperature under hot conditions through vasodilation and sweating.
(2) Humans have a strong ability to adjust to heat.
ii. Body Shape and Adaptation to Heat Stress
(1) Bergmann’s rule: Heat-adapted mammals will have higher surface-area-to-body ratios.
(2) Allen’s rule: Heat-adapted mammals will have long limbs.
(3) Rules explain variation in human body shapes going back 1.5 million years.
iii. Cold Stress and Thermoregulation
(1) The human body struggles to maintain body temperature at cold extremes through vasoconstriction, shivering.
iv. Solar Radiation and Skin Color
(1) Best predictor of skin color is UV radiation exposure.
(2) More pigmentation is associated with high UV.
v. Solar Radiation and Vitamin D Synthesis
(1) The body needs UV radiation to synthesize vitamin D.
(2) Vitamin D is crucial in calcium absorption, bone mineralization.
(3) Deficiencies in vitamin D production can lead to bone malformations, including malformations of the pelvis.
(4) Melanin is the primary influence on vitamin D synthesis. Depending on environment, a person’s melanin type can be advantageous or disadvantageous.
vi. High Altitude and Access to Oxygen
(1) Humans suffer from hypoxia (lack of available oxygen) at high altitudes.
(2) The body responds through production of extra red blood cells and hemoglobin, increasing diameter of blood vessels.
(3) Those born at high altitudes have greater lung volume and larger chest cavities as well as the above characteristics.
c. Nutritional Adaptation: Energy, Nutrients, and Function
i. Each human body requires certain energy and nutrients to function.
(1) Basal metabolic requirement (basic body functioning)
(2) Total daily energy expenditure (energy needed for BMR plus work, exercise, etc.)
ii. Human Nutrition Today
(1) Most populations are undernourished and consume too few calories.
(2) Efforts to combat this problem have resulted in new nutritional issues.
iii. Overnutrition and the Consequences of Dietary Excess
(1) Dietary excess is as serious a problem as dietary lack.
(2) Obesity is an increasing problem in the U.S., especially among children, as well as in the Pacific, Europe, Middle East, Latin America, and South Africa.
(3) Obesity can lead to high cholesterol, heart disease, diabetes.
(4) May have resulted from genetic traits that allowed for conservation of nutrition during times of famine (thrifty genotype)
(5) Examples of this thrifty genotype can be found in Native Americans in the United States.
d. Workload Adaptation: Skeletal Homeostasis and Function
i. Bone growth is affected by disease, physiological processes, nutrition, and mechanical forces.
ii. Wolff’s law states that bone is produced where it is needed and removed where it is not.
iii. Activity or the lack of it can change the shape of skeletal elements.
e. Excess Activity and Reproductive Ecology
i. Benefits of exercise are well documented.
ii. Excessive workload or exercise can interrupt female reproduction, lowering fertility levels.
iii. Excessive workload potentially can lower birthrates in certain groups or populations.
iv. Work or exercise becomes a selective factor in evolution.