About human races

1. About human races • There are obvious biological differences in human beings. • Two important questions about this fact are: • 1) which criteria, which measurable differences, shall we use to set up a typology of races? and • 2) Assuming we can accurately measure human phenotypical physical variation, does this have anything to do with variation in features of human thought or behavior?

2. Classification • On the question of classification, there are historically two very different modes of thinking: • (1) typological thinking and • (2) population thinking

3. Blumenbach’s races • 1775: Johann Friedrich Blumenbach used the term “race” to define divisions of the human species. • He classified humans into five races Caucasian, Mongolian, Ethiopian, American, and Malay. • Blumenbach held that there was but one species of human, but he concluded that humans from the Caucasus region of Asia Minor were aesthetically pleasing.

4. Blumenbach’s race map http://tinyurl.com/oz3h9

5. Typological thinking • Blumenbach classified skulls from around the world by studying detail and selecting a type specimen. • Typological thinking is still with us today.

6. The logical fallacy in typological thinking is a general problem, not confined to the labeling of so-called races. • We see it in the labeling of particular dialects as typical of a language.

7. Population thinking • The remedy for typological studies about races of humans appeared to be population studies. • Measure a large numbers of individuals, and produce means and distributions. • This creates ideal types, the features of which are found in no individual. • And the more precise the measures, the more categories are proliferated.

8. Creating complexity • If there are four races based on color (black, white, yellow, red) and we add one binary feature (like hair texture – wavy and straight) then there are eight races. • Now add two kinds of crania (wide and narrow): there are 16 types. • Sweden, 1898: of 45,000 people, 11% had all the traits usually included in the so-called Nordic race: blond hair, blue eyes, low skin pigmentation, dolicocephaly, and so on.

9. Suppose 20 traits and a criterion that 75% of people have each one. • By trait 2: 75% of 75% is 56% • By trait 10: 1.34% have 75% of the traits. • By trait 20: 317 people out of 100,000 have all the traits. Those are the ideal candidates.

10. We impose typologies • All typologies are arbitrary in some sense. • We impose them on nature to make sense out of a welter of information. Here are seven historical typologies of humans: • 1) cephalic index, or the ratio between the width and the length of the head; 2) the facial index, or the ratio of the length to the width of the face; 3) the nasal index; 4) eye, lip, and ear shape; 5) eye, hair, and skin color and hair texture; 6) stature, weight, and build; and 7) blood groups.

11. Race is a social concept • But every morphological characteristic has a range of variation – a distribution – even within so-called races. • Look, for example, at skin color in the U.S. • Historically, the one-drop rule defined what it meant to be black for many people. • Many Mediterranean people have more melanin in their skin than do many American blacks.

12. Race is a folkloric concept • Race is a folkloric idea that developed in the U.S. out of the debate over slavery. • 17th century, British used Indian slaves on plantations in Barbados and Jamaica. • By the late 17th century, the Indians had died and Britain began bringing slaves from Africa to the plantations in their Caribbean colonies. • Recall: in the early 18th century, the anti-slavery movement in Britain was underway.

13. Establishing the social concept of race • 1854: Types of Mankind published by Josiah Nott (a Southern physician) and George Glidden (the U.S. consul in Cairo). • Nine editions before 1900 helped establish the social concept of race.

14. Social race becomes law • Roger Taney, Chief Justice of the United States Supreme Court in 1859 in the Dred Scott case: • “Negroes were seen only as property; they were never thought of or spoken of except as property” and thus “were not intended by the framers of the Constitution to be accorded citizenship rights.” “The Negro,” Taney said, “is a different order of being.”

15. Science ratifies social race • In the 18th and 19th century, the folk idea of race was ratified by science. • In the 20th century, population thinking and genetics seemed to be the answer: We would recognize that races are not merely ideal types, based on measurements of phenotypic differences, but are populations that are identified by a common gene pool and that tend to preserve that gene pool over time.

16. Genes are distributed across populations, but there are concentrations – that is, the frequency of particular genes varies greatly and it is this fact which changed thinking about races. • Just as everyone is unique phenotypically, so we are all unique genetically, but there are clumps of traits based on genetic frequencies.

17. Sophisticated typological thinking • And so we wound up with a definition of race that was more sophisticated than those of earlier times, but just as flawed. • Here is the scientific definition of race, based on population thinking: • A race is a human population that is sufficiently inbred to reveal a distinctive genetic composition which is observable in a distinctive combination of physical traits.

18. A typology by any other name … • This is just another way of creating typologies. • Human variation is continuous, with no clear boundaries, and race – whether based on ideal types or on genetic populations – tells us little about a person. • The variation within races, at the individual level, are far greater than the variations across the so-called races.

19. Race as a sociopolitical concept • Now we have populations tagged as races, with the tagging becoming more and more sociopolitically motivated. • Biological race does not explain infant mortality among American Indians on the Reservations or among African Americans in the inner cities. • Biological race does not explain the high rate of breast cancer in African American women or the low life expectancy in African American men.

20. Race is ephemeral • In Brazil, rich people who have dark skin and wiry hair are classified in a higher social race than if they were poor. • Skin color as a race marker is ephemeral: Amazonian Indians are darker than North American Indians are.

21. Race, language, class • The concept of race is much like the concept of social class or the concept of English as a language. • Each implies an aggregate of people who have something in common and in each case, diversity among the constituents is put aside.

22. So, the concept of race in humans is a social, not a biological concept. • There are clumps of physical features that define populations, but we don’t have to use skin color to to group geographic populations.

23. Ear wax does very well • Suppose you have to guess whether each of 300 people is from China, Sweden or Kenya. • You can’t see them but you have a sample of their ear wax. • If the wax were dry and crumbly, then guess Chinese. Otherwise, guess not Chinese. Across China, crumbly ear wax occurs in 86-98% of sampled persons, so guessing Chinese produces about one mistake in 10-12 tries. Not a bad score.

24. Crumbly, dry ear wax: 18% of northern Europeans and <5% of Africans south of the Sahara. • So if the sample of ear wax is wet and gooey rather than dry and crumbly, you’d make very few mistakes if you guess that the person was either African or northern European.

25. Duffy factor • Now take a sample of blood. • If there is no Duffy factor in the red blood cells, then guess Kenyan. • Individuals who lack the Duffy factor are not susceptible to Plasmodium vivax. • Duffy factor is present in almost all Chinese and varies across northern European populations from 37% to 82%.

26. Melanin and skin Color • The skin color of all animals is highly plastic. • The case of the English peppered moth: • By the mid-19th century, the Industrial Revolution produces pollution in the English countryside. • Peppered moth splits into becomes two varieties, one melanic, one lighter and the melanic variety predominates by 1896 in the more polluted areas. • Under UV light, the melanic form of the moth is protected from birds.

27. From 1960-1980, the percentage of melanic moths goes from 90% to 10%, as pollution controls take effect.

28. The sparrow was introduced into the U.S. in 1852 from Europe onto the east coast. • Heavier varieties now in the northern, colder areas and the lighter varieties are in southern, warm areas. • 100 sparrow generations. For humans, this would be 2000 years.

29. Skin color and malaria • In humans, melanin is formed in special cells, melanocytes, in the lower epidermis. • Populations father to the north from the equator average less and less melanin production. • Vitamin D production in deep layers of skin and is stimulated by UV light. • In hypovitaminoisis D calcium is not absorbed in the intestines. The nervous system draws needed D from bone and this produces rickets.

30. Rickets widespread in 19th century Europe with industrialization. • Hypervitaminosis D leads to fatal kidney dysfunction. • Light-skinned, northern Europeans can absorb enough UV light to produce vitamin D, but have a higher risk of later-life skin cancer.

31. Hemoglobin: protein in erythrocytes transports oxygen to tissues and returns with carbon dioxide to the lungs. • Hemoglobin molecules are two protein chains. • The 6th amino acid on one chain is glutamic acid. • A mutation at this spot can change the thymine base to adenine – that is, it can change the amino acid from a CTC to a CAC. • This single event is the allele of hemoglobin known as sickle-cell, or HgS.

32. Central Africa: Hemoglobin S molecules crystallize when the oxygen level is low and become twisted. • This is sickle-cell anemia. • 1951: JV Neel showed that carriers of the sickle cell trait are heterozygous. • They have cells with the same property, but it is not severe in terms of response.

33. Two hemoglobins, S and A. • SS die of sickle-cell disease before reproducing; • AA, homozygous normals, more likely to die of malaria • AS heterozygotes less likely to die of malaria. • Balanced polymorphism

34. Balanced polymorphism • 2000 years ago, people began moving into forest from open dry country. • They used metal tools to clear forest patches for agriculture. • This produced densely populated settlements – and standing puddles of water.

35. 1954, AC Allison plots distribution of HbS and malaria parasites – the Plasmodium falciparum and the Plasmodium vivax. • 1967, SL Wiesenfeld (Science) shows correlation between the length of time that agriculture was in a region in Africa and the frequency of the sickle-cell trait.

36. Heterozygotes HbS/HbA resist malaria, creating balanced polymorphism: • Different pressure in various places from malaria, but there is uniform pressure against sickle cell anemia.

37. Homozygotes for sickle-cell disease do not reproduce; heterozygotes have high reproductive success and outnumber the homozygotes by 2:1. • The normal allele and the sickling allele are both kept in the population – as long as malaria is rampant.

38. Sickle cell trait (the heterozygous condition) occurs in just 4% of Americans of African descent. • The apparently rapid dissipation of the sickle-cell trait must be a response to the disappearance of malaria. • This is not to minimize the impact of sickle-cell anemia.

39. PTC tasting • There are many examples of balanced polymorphisms in humans. • One of them is PTC tasting. • Phenylthiocarbamide: chemical close in structure to one found in mustard plants, cabbages, and Brussel spouts. • Overeating these plants interferes with thyroid function; tasting PTC may have an adaptive advantage.

40. We don’t know why indigenous populations in Siberia are up to 60% tasters, while indigenous populations of the Americas have as little as 10% tasters.

41. Lactase deficiency – Lactose intolerance • Another balanced polymorphism is lactase deficiency. • The enzyme lactase breaks down milk sugar, lactose, into simple sugars. • By the time they are four years old, most humans stop secreting lactase and become lactase deficient and lactose intolerant.

42. Drinking unfermented milk then produces a lot of discomfort – bloating, diarrhea, nausea. • This trait keeps adults from competing with infants for milk, but we do not know if this is the adaptive reason for the development of the trait.

43. People who are lactase sufficient consume and produce milk – and have for a very long time. • In northern Europe, animal milk was, prehistorically, one of the only sources of calcium.

44. Out of Africa and lactose tolerance • Moving out of Africa, people 200,000 years ago were probably all lactase deficient. • Lactose tolerance was probably a associated with the movement of pastoral peoples moving into northern Europe from the Mediterranean.

45. Recent micro-evolutionary events • This may have happened just a few thousand years ago. • Lactose, like vitamin D, helps absorption of calcium, but only for people who produce lactase. • Continued production of lactase and lighter skin are both adaptations to higher latitudes.

46. Northern Europe was settled by farmers from the Mediterranean about 6000 years ago. • The pastoralists who came from the Mediterranean were surely heavily melanic. • They would have been able to adapt to the cold of the northern latitudes culturally – by making heavy skin clothing and covering themselves from head to toe.

47. This would have been highly selective for white skin, especially white faces, so that the sunlight could be absorbed and vitamin D could be produced. • Pink cheeks on babies are highly admired among white people. Marvin Harris pointed out that this preference probably comes from a selective advantage. • The pink in pink cheeks is the sight of blood through translucent skin – skin that absorbs maximally the UV sunlight.

48. Producing vitamin D is only half the story. Vitamin D transports calcium to the cells, so people would have needed a good supply of calcium in northern climates – from milk, for example. • And this would require that adults be able to digest milk.

49. Lactose intolerant, pastoral peoples use the lactobacillus to produce fermented milk products like yogurt and cheese (which is more easily absorbed) or they separate the lactose-rich whey from the curds (and feed the whey to babies). • But in the northern areas of Europe, there was a selective advantage for light skin.

50. Some perspective … • Put lactase deficiency and balanced poly-morphisms, like sickle-cell anemia, into perspective. • African Americans have a higher death rate than whites in our society, but sickle cell anemia accounts for three-tenths of one percent of the difference in death rates. • Most of the difference, for those under 30, is in homicide. And most of the difference for those over 50 is poorer health.