6 Human Variation and Adaptation Anthropology Appreciating Human

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6 Human Variation and Adaptation Anthropology: Appreciating Human Diversity 14 th Edition Conrad Phillip

6 Human Variation and Adaptation Anthropology: Appreciating Human Diversity 14 th Edition Conrad Phillip Kottak

2 Human Variation and Adaptation • Race: A Discredited Concept in Biology • Human

2 Human Variation and Adaptation • Race: A Discredited Concept in Biology • Human Biological Adaptation © 2011 The Mc. Graw-Hill Companies, Inc.

3 Human Variation and Adaptation • What is the race concept, and why have

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? © 2011 The Mc. Graw-Hill Companies, Inc.

4 Race: A Discredited Concept in Biology • Historically, scientists approached the study of

4 Race: A Discredited Concept in Biology • Historically, scientists approached the study of human biological diversity in two ways: – Racial classification, no largely rejected – Explanatory approach that focuses on understanding specific differences © 2011 The Mc. Graw-Hill Companies, Inc.

5 Race: A Discredited Concept in Biology Racial classification is the attempt to assign

5 Race: A Discredited Concept in Biology Racial classification is the attempt to assign humans to discrete categories (purportedly) based on common ancestory. Biological differences are real, important and apparent. But not a source to categorize people into race groups. © 2011 The Mc. Graw-Hill Companies, Inc.

6 Race: A Discredited Concept in Biology • Race refers to a geographically isolated

6 Race: A Discredited Concept in Biology • Race refers to a geographically isolated subdivision of a species – 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 © 2011 The Mc. Graw-Hill Companies, Inc.

7 Race: A Discredited Concept in Biology • Clines are gradual genetic shifts and

7 Race: A Discredited Concept in Biology • Clines are gradual genetic shifts and they are not compatible with discrete and separate races. • Phenotype-based racial classifications raise the problem of deciding which traits should be primary. height, weight, body shape, skull form, skin color? © 2011 The Mc. Graw-Hill Companies, Inc.

8 Race: A Discredited Concept in Biology • Phenotypic traits (skin color) have been

8 Race: A Discredited Concept in Biology • Phenotypic traits (skin color) have been used for racial classification – This overly simplistic classification was compatible with the political use of race during the colonial period. – Race kept white Europeans separate from African, Asian, and Native American subjects. © 2011 The Mc. Graw-Hill Companies, Inc.

9 Races Are Not Biologically Distinct • Problems with using a tripartite scheme –

9 Races Are Not Biologically Distinct • Problems with using a tripartite scheme – “Color based” racial labels are not accurate. • Caucasoid, Negroid, Mongoloid – Many populations don’t fit neatly into any one of the three “great races. ” – No single trait can be used as a basis for racial classification. – Phenotypic similarities and differences do not necessarily have a genetic basis. © 2011 The Mc. Graw-Hill Companies, Inc.

10 • The number of combinations is very large – Skin color, stature, skull

10 • The number of combinations is very large – Skin color, stature, skull form, nose form, eye shape, lip thickness don’t go together as a unit • The amount that heredity (versus environment) contributes to phenotypical traits is unclear. © 2011 The Mc. Graw-Hill Companies, Inc.

11 Genetic Markers Don’t Correlate with Phenotype – The analysis of human DNA indicates

11 Genetic Markers Don’t Correlate with Phenotype – The analysis of human DNA indicates that 94 % of human genetic variation occurs within “races”. – There is only 6 % variation between conventional geographic “racial” groupings (Africans, Asians and Europeans). – There is much greater variation within each of traditional “races” than between them. © 2011 The Mc. Graw-Hill Companies, Inc.

12 – Although long-term genetic markers do exist they don’t correlate neatly with phenotype.

12 – Although long-term genetic markers do exist they don’t correlate neatly with phenotype. – Phenotypical similarities and differences are not precisely or necessarily correlated with genetic relationships. – Because of environment that affect individuals during growth and development, the range of phenotypes characteristic of a population may change without any genetic change. © 2011 The Mc. Graw-Hill Companies, Inc.

13 Genetic Markers Don’t Correlate with Phenotype • Conventional geographic “racial” groupings have about

13 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. – Long-term genetic markers exist, but they don’t correlate neatly with phenotype. – Change in height and weight due to changes in dietary practices in a few generations (not race or genetics!) © 2011 The Mc. Graw-Hill Companies, Inc.

14 Explaining Skin Color • Traditional racial classification assumes biological characteristics are determined by

14 Explaining Skin Color • Traditional racial classification assumes biological characteristics are determined by heredity and were stable. – Role of natural selection in producing variation in skin color illustrates an explanatory approach to human biological diversity. © 2011 The Mc. Graw-Hill Companies, Inc.

15 Explaining Skin Color • Skin color biological trait is influenced by several genes.

15 Explaining Skin Color • Skin color biological trait is influenced by several genes. – Melanin: a natural sun screen 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. © 2011 The Mc. Graw-Hill Companies, Inc.

16 Explaining Skin Color • Prior to the 16 th century, very dark skinned

16 Explaining Skin Color • Prior to the 16 th century, very dark skinned populations lived in the 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. © 2011 The Mc. Graw-Hill Companies, Inc.

17 Explaining Skin Color • Loomis: focused on role of UV radiation in stimulating

17 Explaining Skin Color • Loomis: focused on role of UV radiation in stimulating vitamin D • Jablonski and Chaplin: explained how 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 © 2011 The Mc. Graw-Hill Companies, Inc.

18 Recap 6. 1: Advantages and Disadvantages of Dark and Light Skin Color ©

18 Recap 6. 1: Advantages and Disadvantages of Dark and Light Skin Color © 2011 The Mc. Graw-Hill Companies, Inc.

19 • Jablonski: “Loking at Alaska, one would think that the native people should

19 • Jablonski: “Loking at Alaska, one would think that the native people should be pale as ghosts” • Why are not they? – Haven’t inhabited the region very long in geological time. – Their traditional diet supplies sufficient vitamin D. © 2011 The Mc. Graw-Hill Companies, Inc.

20 Human Biological Adaptation • Abundant evidence exists for human genetic adaptation and evolution

20 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. © 2011 The Mc. Graw-Hill Companies, Inc.

21 Genes and Disease • According to the World Health Report, tropical diseases affect

21 Genes and Disease • According to the World Health Report, tropical diseases affect more than 10 percent of the world’s population. – Malaria: 350 million to 500 million people – Schistosomiasis: more than 200 million – Filariasis: 120 million © 2011 The Mc. Graw-Hill Companies, Inc.

22 Genes and Disease • Microbes were the major selective agent for humans, particularly

22 Genes and Disease • Microbes were the 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 the foremost cause of human mortality. – ABO blood groups vary in their resistance to disease. © 2011 The Mc. Graw-Hill Companies, Inc.

23 Genes and Disease • In diseases for which there are no effective drugs,

23 Genes and Disease • In diseases for which there are no effective drugs, genetic resistance maintains significance. – There is probably genetic variation in people’s susceptibility to HIV. – AIDS could cause large shifts in human gene frequencies. © 2011 The Mc. Graw-Hill Companies, Inc.

24 Facial Features • Natural selection also affects facial features. – Long noses seem

24 Facial Features • Natural selection also affects facial features. – Long noses seem to be adaptive in arid areas and cold environments. – Thomson’s Nose Rule: There is an association between nose form and temperature for those who have lived for many generations in the areas they now inhabit. © 2011 The Mc. Graw-Hill Companies, Inc.

25 Size and Body Build • Bergmann’s rule: The smaller of two bodies similar

25 Size and Body Build • Bergmann’s rule: The smaller of two bodies similar in shape has more surface area per unit of weight. – Within the same species of warm-blooded animals, populations having smaller individuals are found more in warm climates. • Allen’s rule: Relative sizes of protruding body parts increase with temperature. © 2011 The Mc. Graw-Hill Companies, Inc.

26 Size and Body Build • Human populations use different, but equally effective, biological

26 Size and Body Build • Human populations use different, but equally effective, biological means of adapting to environmental stresses associated with high altitudes. – Andeans – Tibetans – Ethiopians © 2011 The Mc. Graw-Hill Companies, Inc.

27 Lactose Tolerance • Phenotypic adaptation: adaptive changes that occur during an individual’s lifetime

27 Lactose Tolerance • Phenotypic adaptation: adaptive changes that occur during an individual’s lifetime – Genes and phenotypic adaptation produce a biochemical difference between human groups in their ability to digest large amounts of milk. – There is an adaptive advantage when other foods are scarce but milk is available. © 2011 The Mc. Graw-Hill Companies, Inc.