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System of stratification based on birth. Movement from on

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Title: System of stratification based on birth. Movement from on


1
  • Human Variation and Adaptation

2
Ancient Racial Classifications
  Homer (fl. 1200 - 850 B.C.) Iliad and Odyssey
acknowledge variability Aethiopians People at
the eastern and western edges of the known world
Cubit-men African (?) pygmies   Herodotus
(484?-425? B.C.) Historiae argues for an
environmental cause of variability between human
groups Egyptians have strong skulls due to
exposure Persian skulls are brittle due to the
use of felt hats   Hippocrates (460 - 377 B.C.)
Environmental influences on human variability
are noted in Volume I of Corpus Hippocraticum
Body build and temperment of different peoples
are said to be related to their climate and
life style   Aristotle (384-322 B.C.) Claims
environmental causes of physical variation in
humans   Wooly hair of Aethiopians due to arid
climate Straight hair of Scythians due to
moist air   St. Augustine (354-430) In De
Civitate Dei Contra Paganos he says all men born
everywhere, no matter how strange they appear
to us, are descended from Adam, i.e., are
descended from a single ancestral stock
3
Early Racial Classifications
  Leonardo da Vinci (1452-1519)   Questioned
the environmental hypothesis in accounting for
human variation, suggesting an early
hereditarian argument based on the power of the
mother's seed.   Andreas Vesalius (1514-1564)
Noted a relationship between race and the
shape of the skull
4
Historical Views of Human Variation
  • Two schools of thought developed to explain
    diversity
  • Monogenists believed that all humans were
    descended from a original pair of humans.
  • Polygenists believed that all humans were
    descended from a number of pairs of humans.

5
Racism
  • Based on false belief that intellect and cultural
    factors are inherited with physical
    characteristics.
  • Uses culturally defined variables to typify all
    members of particular populations.
  • Assumes that one's own group is superior.
  • A cultural phenomenon found worldwide.

6
Intelligence
  • Genetic and environmental factors contribute to
    intelligence.
  • Many psychologists say IQ scores measure life
    experience.
  • Innate differences in abilities reflect variation
    within populations, not differences between
    groups.
  • There is no convincing evidence that populations
    vary in regard to intelligence.

7
Types of Human Variation
  • Genetic variation
  • Variation due to genes inherited from the parents
  • Environmental variation
  • Variation caused by environmental factors such as
    culture, climate, habitat, or competition from
    other species

8
The Big Problem with Understanding Human Variation
  • It is very difficult to separate the influences
    of genes, environment, and culture in the
    variation of actual human individuals
  • Variation WITHIN groups can have very different
    causes than variation BETWEEN groups
  • The definition of a biological population in
    modern humans is problematic

9
Influence of Environment
The differences between two separate lawns
planted from the same bag of seed must be
environmental. However, if the seed used was
genetically variable, the differences within each
lawn could be genetic.
10
Figure 16.19
11
Height in British Soldiers
The height of men joining the British army in
1939 varied considerably, illustrating the range
of variation in morphological characters within
populations. The tallest men joining the army
were more than 2 m (84 in., about 7 ft) tall,
while others were less than 1.5 m (60 in., or 5
ft) tall.
12
Historical Views of Human Variation
  • Biological determinism - cultural and biological
    variations are inherited in the same way.
  • Eugenics - "race improvement" through forced
    sterilization of members of some groups and
    encouraged reproduction among others.

13
Traditional Concept of Race
  • Since the 1600s, race has been used to refer to
    culturally defined groups.
  • Race is used as a biological term, but has
    enormous social significance.
  • "Racial traits" are not the only phenotypic
    expressions that contribute to social identity
    sex and age are also critically important.
  • In the 1950's the use of the term "race" was
    replaced with "ethnicity

14
Allele Frequencies Within and Between Populations
  • After World War II, the study of human variation
    shifted to the study of differences in allele
    frequencies within and between populations.
  • The application of evolutionary principles to
    human variation has replaced the view that was
    based solely on observed phenotype.
  • Races are no longer viewed as fixed biological
    entities, composed of individuals fitting a
    particular type.

15
Researchers often use short pieces of DNA called
Alu polymorphisms to determine whether various
populations are related to one another. Alus have
no known function, yet they copy and insert
themselves at random throughout a person's
genome. Because previously inserted Alus do not
excise themselves, Alu patterns can be used as
yardsticks to estimate how close two people--and,
on average, two populations--are genetically.
16
Counting the number of DNA units called short
tandem repeats on chromosomes can allow
scientists to group individuals according to
probable ancestry. One such repeat, AAAG, occurs
between two and seven times in people with
African heritage but between five and eight times
in those whose ancestors came from Europe or the
Middle East. (Every person inherits one set of
repeats from their mother and one from their
father.)
17
Figure 16.22
(a) Evolutionary trees for human populations
based on morphological similarity look very
different from (b) trees based on genetic
similarity.
18
Figure 16.11
This tree, based on the frequencies of 120 genes
in 42 populations from every part of the globe,
is consistent with the hypothesis that humans
originated in Africa and spread from there to the
rest of the globe.
19
Figure 16.12
(a) This model of the expansion of early
anatomically modern human populations generates
the phylogenetic tree shown in (b) if
geographically separate populations remain
genetically isolated.
20
Figure 16.14
(a) This model of the expansion of early
anatomically modern human populations generates
the phylogenetic tree shown in (b). Because
European populations are assumed to be descended
from a relatively recent mixture of African and
Asian populations, the genetic distances between
Europeans and Asians and between Europeans and
Africans is smaller than the distance between
Asians and Africans.
21
Figure 16.13
This tree, based on genes from over 100 loci,
indicates that European populations have
undergone less genetic change than Asian or
African populations. The length of the path
between any two contemporary populations
represents the genetic distance between them. The
fact that the genetic distance between African
and Asian populations is much greater than the
distances between African and European
populations or between Asian and European
populations indicates that European populations
have experienced less genetic change than other
populations.
22
Distribution of Three Genetic Diseases
The distribution of three genetic diseases (PKU,
cystic fibrosis, and Tay-Sachs) illustrates the
existence of variation among human groups.
23
Mendelian Genetics in Humans SLI
The pattern of SLI in the KE family tree suggests
that some cases of specific language impairment
(SLI) are caused by a single dominant gene.
Circles represent women, triangles represent men,
and blue symbols represent people with SLI. If
SLI is caused by a dominant gene, then, since SLI
is rare in the population as a whole, we know
from the Hardy-Weinberg equations that almost all
people with SLI will be heterozygotes. Thus,
Mendels principles tell us that, on average,
half of the offspring of a mating between a
person with SLI and a person without it will have
SLI, and half the offspring will have normal
linguistic skills. Notice how well the family
shown in this tree fits this prediction.
24
Groupings Used by Lewontin in Population Genetics
Study (1972)
25
Adaptive Significance of Human Variation
  • Human variation is the result of adaptations to
    environmental conditions.
  • Physiological response to the environment
    operates at two levels
  • Long-term (genetic) evolutionary changes
    characterize all individuals within a population
    or species.
  • Short-term, temporary physiological response is
    called acclimatization.

26
Skin Color
  • Influenced by three substances
  • Hemoglobin, when it is carrying oxygen, gives a
    reddish tinge to the skin.
  • Carotene, a plant pigment which the body
    synthesizes into vitamin A, provides a yellowish
    cast.
  • Melanin, has the ability to absorb ultraviolet
    radiation preventing damage to DNA.

27
Pigmentation and Geographical Divisions
  • Before 1500, skin color in populations followed a
    geographical distribution, particularly in the
    Old World.
  • Populations with the greatest amount of
    pigmentation are found in the tropics.
  • Populations with lighter skin color are
    associated with more northern latitudes.

28
Skin Pigmentation
This map shows contours in skin color. Notice
that there are smooth gradients away from the
equator.
29
Skin Color
Skin color varies continuously when a
representative sample of the world's populations
is analyzed. In other words, it is impossible to
establish neat categories or "pigeon holes" for
populations or individuals based on this trait
(continued below image).
30
Thermal Environment
  • Mammals and birds have evolved complex
    physiological mechanisms to maintain a constant
    body temperature.
  • Humans are found in a wide variety of thermal
    environments, ranging from 120 F to -60 F.

31
Human Response to Heat
  • Long-term adaptations to heat evolved in our
    ancestors
  • Sweat Glands
  • Vasodilation
  • Bergmann's rule - body size tends to be greater
    in populations that live in cold environments.

32
Human Response to Cold
  • Short-term responses to cold
  • Metabolic rate and shivering
  • Narrowing of blood vessels to reduce blood flow
    from the skin, vasoconstriction.
  • Increases in metabolic rate to release energy in
    the form of heat.

33
Climate and Body Size
People living in colder climates have larger
bodies. The vertical axis plots mean chest girth
for numerous human groups, and the horizontal
axis plots the mean yearly temperature in the
regions in which each group lives. Because chest
girth is a measure of overall size, these data
show that people living in colder climates have
larger bodies.
34
High Altitude
  • Multiple factors produce stress on the human body
    at higher altitudes
  • Hypoxia (reduced available oxygen)
  • Intense solar radiation
  • Cold
  • Low humidity
  • Wind (which amplifies cold stress)

35
Infectious Disease
  • Caused by invading organisms such as bacteria,
    viruses, or fungi.
  • Throughout evolution, disease has exerted
    selective pressures on human populations.
  • Disease influences the frequency of certain
    alleles that affect the immune response.

36
Impact of Infectious Disease
  • Before the 20th century, infectious disease was
    the number one limiting factor to human
    populations.
  • Since the 1940s, the use of antibiotics has
    reduced mortality resulting from infectious
    disease.

37
Malaria
  • Falciparum malaria has historically been the
    leading killer of children and older adults in
    the southern hemisphere
  • Malaria originated as an animal parisite
  • Malarial strains have afflicted human populations
    for many thousands of years
  • Agriculture has significantly spread the disease
    due to sedentism and irrigation

38
Distribution of Hemoglobin S
Hemoglobin S is only common in areas of the world
in which falciparum malaria is prevalent. (a) The
colors show the frequency of hemoglobin S
throughout the world. (b) The regions of the Old
World in which falciparum malaria is prevalent
are in red.
39
Balanced Polymorphism in hemoglobin S
The average fitness of the S allele of hemoglobin
S declines as the frequency of S increases
because more and more S alleles are found in SS
homozygotes. Similarly, the average fitness of
the A allele of hemoglobin A increases as the
frequency of S increases because more and more A
alleles are found in AS heterozygotes. A balanced
polymorphism occurs when the average fitness of
the two alleles is equal.
40
Small Pox
  • The only disease considered to be eliminated as a
    result of medical technology (Polio is close,
    except in Nigeria)
  • Smallpox has a higher incidence in those with
    type A or AB than in those type O blood.
  • The immune systems of individuals with type A
    antigen may not recognize the small pox antigen
    as a threat.

41
Impact of Infectious Disease in the West
  • In the late 1960s, the surgeon general declared
    the war against infectious disease won.
  • Between 1980 and 1992 deaths from infectious
    disease increased by 58.
  • Increases in the prevalence of infectious disease
    may be due to overuse of antibiotics.

42
Environmental Factors.
  • Global warming may expand the range of tropical
    diseases.
  • The spread of disease is associated with
    encountering people this includes crossing
    borders and penetrating remote areas.
  • The increasingly large human population leads to
    overcrowding, unsanitary conditions and the
    spread of communicable disease.

43
Figure 16.09
The LACP gene could have spread in the 7000
years (300 to 350 generations) since the origin
of dairying if the ability to digest lactose as
an adult leads to even as little as a 3 increase
in fitness (s).
44
Dimensions of Stratification
  • Powercontrol resources in ones own interest.
  • Wealthaccumulation of material resources or
    access to the means of producing these resources.
  • Prestigesocial honor or respect.

45
Ascribed Vs. Achieved Status
  • Ascribed Status Social position into which a
    person is born. (sex, race, kinship group)
  • Achieved Status Social position that a person
    chooses or achieves. (professor, criminal, artist)

46
Social Class in the United States
  • Status depends on occupation, education, and
    lifestyle.
  • The American Dream, is based on the democratic
    principle of equality and opportunity for all.
  • Social class in the United States correlates with
    attitudinal, behavioral, and lifestyle
    differences.

47
Caste System
  • System of stratification based on birth.
  • Movement from one caste to another is not
    possible.
  • Castes are hereditary, endogamous, ranked in
    relation to one another and usually associated
    with a traditional occupation.

48
Hindu Caste System
  • Four caste categories
  • Brahmins - priests and scholars
  • Kshatriyas - ruling and warrior caste
  • Vaisyas - the merchants
  • Shudras - menial workers and artisans
  • Harijans untouchables

49
U.S. Racial Stratification Systems
  • Race is constructed on the basis of skin color
    and presumed ancestry.
  • Divides people into blacks and whites
    ignoring the reality of the skin color spectrum.
  • By the 20th century, the system of race in the
    American south was very similar to the caste
    system in India.

50
Race Stratification in the U.S. and Brazil
  • Two largest multiracial societies in the
    Americas.
  • In both societies the legacy of slavery continues
    in the form of racial inequality.
  • Brazil 45 of nonwhite families and 25 of
    white families live below the poverty line.
  • U.S. 30 of nonwhite families and 8 of white
    families live below the poverty line.

51
Figure 16.20
This contour map of overall genetic similarity is
based on a sample of 120 genes from 42
populations assembled by Cavalli-Sforza and his
colleagues. The fact that the contours of equal
genetic similarity are roughly evenly spaced
indicates that there is a smooth east-to-west
gradient of overall genetic similaritythere are
no sharp boundaries between groups. Sharp
boundaries would produce a map in which many
contour lines would be positioned closely
together. This map is drawn from the same data
used to construct the tree shown in Figure 16.11.
52
The Genetics of Race Summary
  • The outward signs on which most definitions of
    race are based--such as skin color and hair
    texture--are dictated by a handful of genes. But
    the other genes of two people of the same "race"
    can be very different. Conversely, two people of
    different "races" can share more genetic
    similarity than two individuals of the same race.
  • Nevertheless, scientists can use genetics to sort
    most large populations according to their
    ancestral geographic origin. This approach does
    not work as well for populations resulting from
    recent mixing with other groups, however.
  • The medical implications of racial genetic
    differences are still under debate.

53
The Social Reality of Race
But genetics cannot prove that race doesn't
exist, Troy Duster explains. No amount of logic
will erase the concept or destroy the disparities
that arise from it, because people use race to
sort their social groupings and to define their
social and economic interactions. Moreover, they
do so in ways that have significant biological
consequences. Sally Lehrman, Scientific American
Feb. 2003
54
Perspectives in Ethnicity
  • Essentialist - ethnicity comes from historical,
    demographic, and economic conditions.
  • Constructionalist - ethnicity comes from
    responses to changing realities within the group
    and in the society of which it is a part.

55
European Colonial Laws
  • Defined acceptable behavior.
  • Established written penal codes, constitutions,
    and western-style courts.
  • Many colonial laws involved restraints on
    sexuality.

56
U.S. Cultural Diversity
  • Native Americans
  • European immigrants - Dutch, Spanish, French, and
    English.
  • Africans - brought to the new colony as slaves.

57
Ethnic Identify
  • Changes as social and economic circumstances
    change.
  • Provides a basis for group solidarity despite
    differences within the group.

58
Incorporating Immigrants Into Society
  • Assimilation model
  • Melting pot model
  • Mosaic Model

59
Assimilationist Model
  • Immigrants should abandon traditions and become
    absorbed in American culture.
  • Resulted in the building of urban Settlement
    Houses, designed to teach immigrants American
    ways.

60
Assimilationist and Immigration
  • Supported minimal immigration to the U.S.
  • Nations seen as similar to the U.S., Such as
    England, were allowed almost unrestricted
    immigration.
  • Nations seen as different to the U.S., Such as
    Greece and Poland, were allowed minimal
    immigration.
  • Immigration of Asians was all but completely
    halted.

61
Assimilation and Native Americans
  • In the mid-19th century, forced onto
    reservations, Indians became a captive audience
    for the teaching of American values.
  • By early 1870s, it was clear that the reservation
    policy had not transformed Indians into
    mainstream Americans.

62
Melting Pot Model
  • Immigrants will melt together into a new American
    culture.
  • By the late 1950s, it was clear that the melting
    pot theory had only limited application.
  • Excluded Asians, Native Americans, Mexican
    Americans, and African Americans.

63
Mosaic Model
  • Cultural diversity is a positive aspect of
    American national identity.
  • Arose in response to the swell of immigration in
    the past 25 years.
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