Download Race: A Discredited Concept in Biology - McGraw

5
1
Human Variation
and Adaptation
Anthropology:
The Exploration of Human Diversity
11th Edition
Conrad Phillip Kottak
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
2
Human Variation
and Adaptation
• Race: A Discredited Concept in Biology
• Human Biological Adaptation
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
3
Race: A Discredited
Concept in Biology
• Race refers to geographically isolated
subdivision of a species
– Members of race or subspecies share
distinctive physical characteristics based
on common ancestry and inheritance of
same genes
Human populations have
not been isolated enough
from one another to
develop into discrete races
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
4
Race: A Discredited
Concept in Biology
– Human populations vary biologically, but
because of extensive gene flow and
interbreeding, there are no sharp breaks
between populations
• Human biological variation distributed gradually
between populations along clines
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
5
Race: A Discredited
Concept in Biology
– Scientists have trouble grouping people
into distinct racial units
• Race is supposed to reflect shared genetic
material
Early scholars used phenotypical traits (skin
color) for racial classification
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
6
Race: A Discredited
Concept in Biology
• Races Are Not Biologically Distinct
– Obvious problem with “color-based” racial
labels is that terms don’t accurately
describe skin color
– Another problem with tripartite scheme is
that many populations don’t neatly fit into
one of the three “great races”
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
7
Race: A Discredited
Concept in Biology
– Racial classifications based on phenotype
lack credibility because similarities and
differences don’t necessarily have genetic
basis
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
8
Race: A Discredited
Concept in Biology
• Explaining Skin Color
– Natural selection—process by which
nature selects the forms most fit to survive
and reproduce in a given environment
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
9
Race: A Discredited
Concept in Biology
• Explaining Skin Color
– Skin color influenced by several genes
• Melanin—primary determinant of human skin
color; chemical substance manufactured in the
epidermis
Prior to 16th century, darker skinned
populations closest to the equator
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
Race: A Discredited
Concept in Biology
10
• Explaining Skin Color
– Skin color influenced by several genes
• Unprotected humans in tropics face threat of
severe sunburn
– Increases susceptibility to disease
– Impairs the body’s ability to withstand heat by
reducing the skin’s ability to sweat
– Light skin is more susceptible to skin cancer.
Loomis suggested that in tropics, dark skin color
protects body against overproduction of vitamin D
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
11
Human Biological Adaptation
• Abundant evidence for human genetic
adaptation and evolution through
selection working in specific
environments
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
12
Human Biological Adaptation
• Genes and Disease
– According to World Health Report, tropical
diseases affect more than 10 percent of
world’s population
• Malaria—300 million to 500 million people
• Schistosomiasis—more than 200 million
• Filarisasis—120 million
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
13
Human Biological Adaptation
• Genes and Disease
– Microbes major selective agent for
humans, particularly before arrival of
modern medicine
• After food production emerged, infectious
diseases pose mounting risk and became
foremost cause of human mortality
• ABO blood groups vary in resistance to disease
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
14
Human Biological Adaptation
• Genes and Disease
– In diseases for which there are no effective
drugs, genetic resistance maintains
significance
• There is probably genetic variation in
susceptibility to HIV
AIDS could cause large shifts in
human gene frequencies
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
15
Human Biological Adaptation
• Facial Features
– Natural selection also affects facial
features
• Long noses seem to be adaptive in arid areas
and cold environments
• Thomson’s Nose Rule—association between
nose form and temperature
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
16
Human Biological Adaptation
• Size and Body Build
– Bergmann’s rule—smaller of two bodies
similar in shape has more surface area per
unit of weight
• Average body size tends to increase and cold
areas and decrease in hot ones
– Allen’s rule—relative size of protruding
body parts—ears, tails, bills, fingers, toes,
and limbs—increase with temperature
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
17
Human Biological Adaptation
• Size and Body Build
– Human populations use different, but
equally effective, biological means of
adapting to environmental stresses
associated with high altitudes
McGraw-Hill
© 2005 The McGraw-Hill Companies, Inc.
18
Human Biological Adaptation
• Lactose Tolerance
– Phenotypical
adaptation—adaptive
changes that occur during
individual’s lifetime
– Genes and phenotypical
adaptation work together to
produce a biochemical
difference between human
groups in ability to digest
large amounts of milk
McGraw-Hill
Adaptive
advantage
when other
foods are
scarce and milk
available
© 2005 The McGraw-Hill Companies, Inc.