Anthropology Appreciating Human Diversity Fifteenth Edition Conrad Phillip

Anthropology Appreciating Human Diversity Fifteenth Edition Conrad Phillip Kottak University of Michigan 6 -1

C H A P T E R HUMAN VARIATION AND ADAPTATION 6 -2

HUMAN VARIATION AND ADAPTATION • Race: A Discredited Concept in Biology • Human Biological Adaptation 6 -3

HUMAN VARIATION AND ADAPTATION • What is the race concept, and why have anthropologists rejected it? • How does natural selection work on contemporary and recent human populations? • Does biological adaptation occur during an individual’s lifetime? 6 -4

RACE: A DISCREDITED CONCEPT • Historically, scientists approached the study of human biological diversity in two ways: • Racial classification, now largely rejected • Explanatory approach 6 -5

RACE: A DISCREDITED CONCEPT • Racial classification: attempt to assign humans to discrete categories (purportedly) based on common ancestry • Human biological variation distributed gradually between populations is called clines • Human populations have not been isolated enough from one another to develop into discrete groups 6 -6

RACE: A DISCREDITED CONCEPT • Phenotypic traits (skin color) have been used for racial classification • Overly simplistic classification compatible with political use of race during the colonial period • Race kept white Europeans separate from African, Asian, and Native American subjects 6 -7

RACES ARE NOT BIOLOGICALLY DISTINCT • Problems with using a tripartite scheme • “Color based” racial labels are not accurate • Many populations don’t fit neatly into any one of the three “great races” • No single trait can be used as basis for racial classification • Phenotypic similarities and differences do not necessarily have genetic basis 6 -8

GENETIC MARKERS DON’T CORRELATE WITH PHENOTYPE • Conventional geographic “racial” groupings have about a 6% variation in genes • Humans are more alike genetically than other hominoids • Haplogroup: lineage or branch of a genetic tree marked by one or more specific genetic mutations • Long-term genetic markers exist, but they don’t correlate neatly with phenotype 6 -9

EXPLAINING SKIN COLOR • Traditional racial classification assumes biological characteristics are determined by heredity and are stable • Role of natural selection in producing variation in skin color offers explanatory approach to human biological diversity 6 -10

EXPLAINING SKIN COLOR • Skin color is a complex biological trait influenced by several genes • Melanin: a “natural sunscreen” produced by skin cells responsible for pigmentation • By screening out ultraviolet (UV) radiation from sun, melanin offers protection against a variety of maladies, including sunburn and skin cancer 6 -11

EXPLAINING SKIN COLOR • Before 16 th century, very dark-skinned populations lived in tropics: a belt extending about 23 degrees north and south of the equator • Outside the tropics, skin color tends to be lighter • Melanin confers a selective advantage on darker-skinned people living in the tropics 6 -12

EXPLAINING SKIN COLOR • Loomis: focused on role of UV radiation in stimulating vitamin D • Jablonski and Chaplin: explained geographic distribution of skin color involved effects of UV on folate, used to manufacture folic acid • Variation in human skin color: • Protects against all UV hazards • Provides an adequate supply of vitamin D 6 -13

RECAP 6. 1: Advantages and Disadvantages (Depending on Environment) of Dark and Light Skin Color 6 -14

THE AAA RACE PROJECT • AAA Race Project: “RACE Are We So Different? ” • Race is a recent human invention • Race is about culture, not biology • Race and racism are embedded in institutions and everyday life 6 -15

HUMAN BIOLOGICAL ADAPTATION • Abundant evidence exists for human genetic adaptation and evolution through selection working in specific environments • With thousands of human genes known, new genetic traits are being discovered every day 6 -16

GENES AND DISEASE • World Health Organization (WHO) report: about one billion people worldwide are affected by neglected tropical diseases • Malaria: 216 million • Schistosomiasis: more than 200 million • Filariasis: 120 million 6 -17

GENES AND DISEASE • Microbes major selective agent for humans, particularly before the arrival of modern medicine • After food production emerged 10, 000 years ago, infectious diseases posed a mounting risk and became foremost cause of human mortality • ABO blood groups vary in resistance to disease 6 -18

GENES AND DISEASE • In diseases for which there are no effective drugs, genetic resistance maintains significance • There is genetic variation in people’s susceptibility to HIV 6 -19

FACIAL FEATURES • Natural selection affects facial features • Long noses seem to be adaptive in arid areas and cold environments • Thomson’s nose rule: association between nose form and temperature for those who have lived for many generations in areas they now inhabit 6 -20

SIZE AND BODY BUILD • Bergmann’s rule: smaller of two bodies similar in shape has more surface area per unit of weight • Within warm-blooded animals, populations with smaller individuals in same species are more often found in warm climates • Allen’s rule: relative sizes of protruding body parts increase with temperature 6 -21

SIZE AND BODY BUILD • Human populations use different biological means of adapting to environmental stresses associated with high altitudes • Andeans • Tibetans • Ethiopians 6 -22

LACTOSE TOLERANCE • Phenotypic adaptation: adaptive changes that occur during an individual’s lifetime • Biochemical difference among human groups involves the ability to digest large amounts of milk • There is an adaptive advantage when foods are scarce but milk is available 6 -23