Transcript Adaptive Significance of Human Variation

Chapter 15
Modern Human Biology:
Patterns of Adaptation
Chapter Outline
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
The Adaptive Significance of Human
Variation
Infectious Disease
Adaptive Significance of Human
Variation

Human variation is the result of adaptations
to environmental conditions.
 Physiological response to the environment
operates at two levels:
1. Long-term (genetic) evolutionary changes
characterize all individuals within a population or
species.
2. Short-term, temporary physiological response is
called acclimatization.
Pigmentation
and Geographical Divisions
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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.
Distribution of Skin Color
Among Indigenous
Populations
Skin Color
Influenced by three substances:
1. Hemoglobin, when it is carrying oxygen,
gives a reddish tinge to the skin.
2. Carotene, a plant pigment which the body
synthesizes into vitamin A, provides a
yellowish cast.
3. Melanin, has the ability to absorb
ultraviolet radiation preventing damage to
DNA.
Production of Vitamin D
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.
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.
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.
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)
Infectious Disease
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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.
Small Pox

The only disease considered to be eliminated
as a result of medical technology
 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.
Impact of Infectious Disease
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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.
Impact of Infectious Disease
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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.
Zoonoses and Human
Infectious Disease