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Chapter 6: Modern Human Variation (Natural Selection in Human Populations…
Chapter 6: Modern Human Variation
The Future of Human Variation
Greater genetic control over human population may be possible in future
Cloning- creating exact replicas
Genetic engineering- swapping genes, in humans it eliminates certain genes
Creation of 'perfect people' is an ethical question
Diversity is needed to continue to evolve
Cultural Diversity
Culture is learned, influences evolution
Culture can change more rapidly than genetic change
Agency: can choose to accept or modify cultural components, based on own needs, perceptions, wants
Culture change: high proportion of population alters beliefs/ behaviours
Post AD 1500- cultural change influenced by Western society and ideals
Most studies focus on external stimuli, but culture actually changes from the inside
The Race Issue
Biological varieties = morphological difference between populations, due to natural selection and drift
Race=sub-species, not classifiable into discrete groups based on biological traits
Not applicable to humans, because human traits are clinal, not discrete (e.g. Skin colour)
Race as a Social construct
"Us" vs. "Them"
Belief that some people are inherently inferior to others
Used to discriminate against certain groups
Current use by law enforcement and forensic scientists ("race as ethnicity")
Myths of Racism
West African Kingdoms- Ghana AD 770, part of trans-Sahara trade network, gold stores
Shang Dynasty, China 1600-1046 BC, Complex government, large scale agriculture, inscriptions on bone
Germ Theory: First Nations had no immunity to European diseases, decimated population. Spanish introduced smallpox to Aztecs, 50% mortality, possible deliberate spreading of infectious diseases
Intelligence does not differ between races (Phillipe Rushton), IQ test are not a measure of intelligence, but show economic and social disparity
Biological Diversity
Humans adapt by
Learned behaviours
Species wide physiological changes
Population specific genetic traits
Body Build/Size
Varies due to temperature of home environment
Bergmanns Rule:
slender species will inhabit warmer climates; robust species will inhabit cooler climates
Allens Rule
: Protruding body parts (limbs) relatively short in cooler areas, relatively longer in warmer areas
Facial structure
Rats: wider faces with narrower nostrils when raised in cold conditions
Same in humans? Long narrow noses in populations living in colder climates (humidifies/warms air before it reaches lungs)
Skin Colour
Amount of pigment melanin and amount of blood in vessels
Not indicative of ancestry
Hypothesis: melanin related to climate
Gloger's Rule:
mammals and birds living in warmer climates = darker skin/fur/feathers compared to cooler areas
Dark Skin:
UV protection, cancer protection
Light Skin:
Vitamin D absorption; reduce damage from frostbite
Lactase Deficiency
Lactase production stops in adolescence
Lactose intolerance is normal worldwide
Lactase persistance in some populations (e.g. Mongolia)
Genetic Variation:
populations evolved lactase gene to produce proteins to break down milks sugar
Cultural Variation:
populations developed ways to process raw milk into cheese or yogurt, reducing lactase, increasing digestibility
High Altitude Living
10 000+ feet above sea level
Puts major stresses on the body
Hypoxia:
Oxygen deficiency, rapid breathing and heart rate, extreme cold, winds, solar radiation, low humidity
Old hypothesis: high altitude populations evolved larger lung capacity, increased surface are of lung capillaries
Current hypothesis: Acclimatization to hypoxia and other conditions
Height
Heredity plays a significant role in height
Secular Trend:
Increase in height globally
Differences in height between populations, some influence by temperature
Partly nutrition and disease (socioeconomic)
Susceptibility of Disease
Long duration and multiple exposures = human populations built immunity to various diseases, = genetic resistance to disease
VIrgin soil epidemic
No previous immunity in a population
Disease affects all members equally (Spanish influenza killed 21 million)
Founder Effect: Viruses adapt to host, and when the adapted virus is passed on it is deadlier to the new genetically similar host
Human Behaviour: disease patterns related more to behaviour than genetics
Sickle-cell anemia
Abnormally produced red blood cells, don't hold oxygen & move poorly through body, causing damage to heart, lungs, brain
Homozygous individuals: have sickle-cell anemia, short survival period
Heterozygous individual: carrier, mild symptoms, confers resistance to malaria (= balancing selection)
Type II Diabetes
Non-insulin dependent , in adults with a sedentary lifestyle, chronic obesity, excess sugar intake
Common in First Nations populations, more common in women and girls
"Thrifty Gene": Retaining high calories for lean times
Natural Selection in Human Populations
Adaptive genes: confer higher survivability & reproductive success in a given environment, heritable
Directional Selection: Causal relationship between a phenotype and fitness (dark moth selected as most fit)
Normalizing Selection: Intermediate phenotypes are more fit compared to extreme phenotypes ( birth weights)
Balancing Selection: Heterozygous individuals are favoured, homozygous individuals are selected against (Sickle-cell anemia)
Physical Environmental Variation: e.g. Speckled moth, physical environment altered the gene frequency of the black moth (genetic change)
Phenotypic Plasticity: Environment can influence a change in phenotype without altering genes
Acclimatization: Physiological adjustments in human individuals to environmental conditions. Occurs over a lifetime
Cultural Environment: Alters physical environment, may lessen need for genetic adaptations and acclimatizing ( modify microenvironment-in cold places, wear clothes, build fires)
Cultural influence on variation: modified behaviours and practices that lead to physical variation (Skull binding by Incas)