Download Race - WordPress.com

6
Human Variation
and Adaptation
Anthropology:
Appreciating Human Diversity
14th Edition
Conrad Phillip Kottak
2
Human Variation and Adaptation
• Race: A Discredited Concept in Biology
• Human Biological Adaptation
© 2011 The McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
4
Race: A Discredited
Concept in Biology
• Historically, scientists
approached the study of human
biological diversity in two ways:
– Racial classification,
now largely rejected
– Explanatory approach
that focuses on
understanding specific
differences
© 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.
© 2011 The McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 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.
© 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.
© 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.
© 2011 The McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
16
Explaining Skin Color
• Prior to the16th 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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
18
Recap 6.1: Advantages and Disadvantages
of Dark and Light Skin Color
© 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.
© 2011 The McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.
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 McGraw-Hill Companies, Inc.