HUMAN BIOLOGICAL DIVERSITY
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Human Variation
Human variation:
Human variation:
Human variation represents an evolutionary continuum, not discrete categories
Humans are uniquely flexible, or adaptable, to environmental conditions
Adaptation occurs before and during the human life cycle
Adaptation is the key to understanding modern human variation
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Adaptation
Adaptation:
Adaptation to the environment occurs at four levels
Genetic- Population level
Developmental- individual level during growth and development
Acclimatization- any time during a lifetime
Behavioral- culture
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Slide 4
Growth and Development: Conception through Adulthood
Growth and Development: Conception through Adulthood
The human lifecycle occurs in 2 stages:
Prenatal- gestation and birth
Postnatal- from birth through puberty and adolescence
Adult- Post-adolescene to senescence
Prenatal Stage: Sensitive to Environmental Stress, Predictive of Adult Health
Involves rapid growth and development, especially of the brain
Prebirth stressors can influence diseases a person may develop later in life
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Slide 5
Growth and Development: Conception through Adulthood
Growth and Development: Conception through Adulthood
Postnatal Stage: The Maturing Brain, Preparing for Adulthood
Development of brain, dentition, motor and cognitive skills, sexual dimorphism, skeletal structure
Environmental effects during childhood influence growth and development
Adult Stage: Aging and Senescence
Aging refers to social, cultural, biological events that occur over a lifetime
Senescence is a reduction of the bodyâs ability to respond to stress (homeostasis)
Cessation of reproduction in women is called menopause
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Slide 6
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Slide 7
Evolution of Human Life History
Evolution of Human Life History
Survival and adaptive success are due to food acquisition and reproduction
Humans are influenced by culture; life history develops with human culture
Prolonged Childhood:
Humans have a prolonged childhood with high maternal investment
Grandmothering: Part of Human Adaptive Success
Postreproductive survival is high with humans
Women play a large role in caring for childrenâs children
Selection for longevity
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The Race Concept
Is Race a valid, biologically meaningful concept?
Is Race a valid, biologically meaningful concept?
So-called racial traits are not concordant
Robert Lewontin studied global genetic variation
Racial groups accounted for only 5â10 percent of variation
Most variation is between groups, not within groups
Human Variation: Geographic cline, not racial categories
Specific biological traits follow a geographical gradient (cline)
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Adaptation Genetic and Developmental
Bergmannâs Rule:
Bergmannâs Rule:
Body size tends to be greater in populations that live in colder climates
As mass increases, the relative amount of surface area decreases proportionately
Increased mass allows for greater heat retention and reduced heat loss
The opposite is true in response to consistently hot environments
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Slide 10
Allenâs Rule:
Allenâs Rule:
In colder climates shorter appendages, are adaptive because they are more effective at preventing heat loss
Conversely, longer appendages, are more adaptive in warmer climates because they promote heat loss
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Slide 11
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Bergmanns Rule and Allens Rule
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Adaptation Acclimitization
Acclimatization: Physiological response during oneâs lifetime to environmental stress
Acclimatization: Physiological response during oneâs lifetime to environmental stress
Example: High Altitude and Access to Oxygen
Humans suffer from hypoxia (lack of available oxygen) at high altitudes
The body responds through production of extra red blood cells and hemoglobin, increases diameter of blood vessels
Those born at high altitudes have greater lung volume and larger chest cavities as well as the above characteristics
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Slide 14
Race is the erroneous classification of human variation
Race is the erroneous classification of human variation
Modern concepts of race began to develop in the 1600âs:
Linnaeus named 5 races
Used clothing, âcharacterâ, behavior to classify groups of people
Blumenbachâs study of skulls in 1775 set a racial taxonomy
Debunking the Race Concept: Franz Boas
Among the first to challenge the taxonomy of human variation
Founded modern American Anthropology
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Adaptation genetic
Solar Radiation and Skin Color
Before 1500, skin color in populations followed a geographical distribution (Clines), particularly in the Old World:
Best predictor of skin color is UV radiation exposure
More pigmentation is associated with high UV
Populations with the greatest amount of pigmentation are found in the tropics (Equatorial regions)
Populations with lighter skin color are associated with more northern latitudes
Clinal Distribution
Why?
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Slide 16
Skin pigmentation:
Skin pigmentation:
Influenced by three substances
Hemoglobin- when it is carrying oxygen it 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
Modern humansâ skin colors range from very light to very dark If all the variants were lined up from lightest to darkest, it would be hard to determine the dividing lines between so-called racial categories In fact, the number of racial categories differs by whom you ask, from three to ten or more Although skin color is an easily observable form of variation among humans, it is not the main form Most of our variation as a species is invisible to the naked eye and does not divide up into discrete categories
Slide 17
Melanocyte cells- produce and distribute melanosomes, which produce skin pigmentation
All humans have the same number of melanocytes
Density of melanin- UV light reflection and absorption
Directly related to UV light
Most variation is across regions
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Slide 18
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Clinal distribution of skin Pigmentation variation
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Slide 20
Selective Pressures:
Selective Pressures:
Folic Acid
Found in B vitamins
Required for the synthesis of DNA
Destroyed by UVA rays
Deficiencies linked to miscarriage and brain spinal cord defects
Vitamin D
Largely derived from sunlight
Key to bone growth
Deficiencies linked to higher rates of cancer, diabetes, cardiovascular disease, ricketsâ¦
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Skin Pigmentation and Vitamin D
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Vitaimin D Deficiency
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Race
Race is not real but racism is very much a reality
Race is not real but racism is very much a reality
Conflict and slavery were previously based on class
Colonialism, competition for resources and economics
Evolutionary thought has been skewed for racist purposes
Eugenics
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Reality
Between 83 and 97% of genetic variation is within populations
Between 83 and 97% of genetic variation is within populations
3 to 17% between populations
Humans are among the least genetically diverse mammals on the planet
Most variation is found in Africa- humans have been there longest
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BIOCULTURAL APPROACH
Modern human variation best explained using a biocultural perspective
Modern human variation best explained using a biocultural perspective
Natural selection provides variation
Human culture alters environments, and thus selective pressures
Disease is major influence on human diversity (and limiting factor to population growth before 20th century)
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