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1. SOC111
INTRODUCTION TO ANTHROPOLOGY
Human Variation
and Adaptation

2. 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?

3. 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

4. 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.

5. Race: A Discredited
Concept in Biology
• Race refers to a geographically
isolated subdivision of a species
–Human populations have not
been isolated enough from one
another to develop into discrete
groups

6. Race: A Discredited
Concept in Biology
• Phenotypic traits (skin color) have been used
for racial classification
White
Black
Yellow
– 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.

7. 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.

8. 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.

9. Genetic Markers Don’t
Correlate 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

10. • Traditional racial classification assumes
biological characteristics are determined
by heredity and were stable over many
generations.
• Role of natural selection in
producing variation in skin
color illustrates an explanatory
approach to human biological diversity.

11. 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.

12. How can we explain the geographic
distribution of 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.

13. Explaining Skin Color
• Geographic distribution of skin color
involved effects of UV on folate.
• Folate is needed for cell division and
the production of new DNA.
• Folate deficiency can cause male
sterility.

14. • The discussion of skin color shows that,
common ancestry is not the only reason
for biological similarities.
• Natural selection makes a major
contribution to variations in human skin
color, as well as to many other human
biological differences and similarities.

15. 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.

16. 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 (snail fever): more than
200 million
–Filariasis: 120 million

17. 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.

18. Genes and Disease
• Smallpox had been a major threat to humans
and a determinant of blood frequencies until
1977.
• The A B 0 blood groups have figured in human
resistance to smallpox.
• People with A or AB blood type are more
susceptible to smallpox than are people with
type B or type 0.

19. Genes and Disease
• Associations between A B 0 blood types and
noninfectious disorders also have been noted.
• Type 0 – duodenal and gastric ulcers.
• Type A – stomach and cervical cancer and
ovarian tumors.
• However, since these noninfectious disorders
tend to occur after reproduction has ended,
their relevance to adaptation and evolution
through natural selection is doubtful.

20. 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.

21. 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.

22. Phenotype Differences
• Tropical climates- slender bodies
with long limbs are advantageous.
• North polars – Eskimos with short
limbs and stocky bodies.
• Altitudes also affects phenotypes.

23. Lactose Tolerance
• Another difference between human groups.
• Lactose tolerence is important factor for
survival when other foods are scarce and milk
is available.
• Lactose tolerance appears to be one of many
aspects of human biology governed both by
genes and by phenotypical adaptation to
environmental conditions.