1. 6 Human Variation and Adaptation Anthropology: Appreciating Human Diversity 14 th Edition Conrad Phillip Kottak

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

3. © 2011 The McGraw-Hill Companies, Inc. 3 Human Variation and Adaptation How does natural selection work on contemporary and recent human populations? Does biological adaptation occur during an individual’s lifetime? What is the race concept, and why have anthropologists rejected it?

4. © 2011 The McGraw-Hill Companies, Inc. 4 Race: A Discredited Concept in Biology –Racial classification, now largely rejected –Explanatory approach that focuses on understanding specific differences Historically, scientists approached the study of human biological diversity in two ways:

5. © 2011 The McGraw-Hill Companies, Inc. 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.

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

7. © 2011 The McGraw-Hill Companies, Inc. 7 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? Race: A Discredited Concept in Biology

8. © 2011 The McGraw-Hill Companies, Inc. 8 Race: A Discredited Concept in Biology –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. Phenotypic traits (skin color) have been used for racial classification

9. © 2011 The McGraw-Hill Companies, Inc. 9 Races Are Not Biologically Distinct –“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. Problems with using a tripartite scheme

10. © 2011 The McGraw-Hill Companies, Inc. 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.

11. © 2011 The McGraw-Hill Companies, Inc. 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.

12. © 2011 The McGraw-Hill Companies, Inc. 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.

13. © 2011 The McGraw-Hill Companies, Inc. 13 Genetic Markers Don’t Correlate with Phenotype –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!) Conventional geographic “racial” groupings have about a 6% variation in genes

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

15. © 2011 The McGraw-Hill Companies, Inc. 15 Skin color biological trait is influenced by several genes. Explaining Skin Color –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.

16. © 2011 The McGraw-Hill Companies, Inc. 16 Prior to the16 th century, very dark skinned populations lived in the tropics: a belt extending about 23 degrees north and south of the equator. Explaining Skin Color –Outside the tropics, skin color tends to be lighter. –Melanin confers a selective advantage on darker-skinned people living in the tropics.

17. © 2011 The McGraw-Hill Companies, Inc. 17 Loomis: focused on role of UV radiation in stimulating vitamin D Explaining Skin Color 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

18. © 2011 The McGraw-Hill Companies, Inc. 18 Recap 6.1: Advantages and Disadvantages of Dark and Light Skin Color

19. © 2011 The McGraw-Hill Companies, Inc. 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.

20. © 2011 The McGraw-Hill Companies, Inc. 20 Human Biological Adaptation With thousands of human genes known, new genetic traits are being discovered every day. Abundant evidence exists for human genetic adaptation and evolution through selection working in specific environments.

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

22. © 2011 The McGraw-Hill Companies, Inc. 22 Genes and Disease –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. Microbes were the major selective agent for humans, particularly before the arrival of modern medicine.

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

24. © 2011 The McGraw-Hill Companies, Inc. 24 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. Natural selection also affects facial features.

25. © 2011 The McGraw-Hill Companies, Inc. 25 Size and Body Build –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. Bergmann’s rule: The smaller of two bodies similar in shape has more surface area per unit of weight.

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

27. © 2011 The McGraw-Hill Companies, Inc. 27 Lactose Tolerance –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. Phenotypic adaptation: adaptive changes that occur during an individual’s lifetime