PSY 3126 Lecture Notes - Lecture 12: Lactase, Protective Factor, Universal Health Care
28 Apr 2018
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November 22, 2017
Physical Health
Human Biological Variability
Human biology varies across cultures, and such variability has two different explanations/mechanisms:
-Innate biological differences: result of selection pressures
-Acquired biological differences: cultural effects on one’s biology, independent of genes
Innate Biological Variability
Humans, like all organisms, evolve due to selective pressures in their environments
-NB: humans are less genetically distinct from each other when compared with other species, but different
populations of humans do differ from each other in many of their genes
Different environments have different selection pressures, leading different populations to evolve different traits
-NB: there is still a greater genetic variation within Africans (who have had up to 200 000 years to accumulate
genetic changers) than between Africans and people of other cultural backgrounds (only up to 60 000 years to
accumulate changes)
The most salient example of genetic variability of humans across different populations is skin colour
-Skin colour is an example of geographical influences on population variation in the human genome
-As you move away from the equator, people become fairer
-People along the equator have adapted to the increased UV levels by having darker skin in order to better protect
themselves
-People living in areas with less UV radiation adapted to have lighter skin in order to still be able to absorb a
sufficient amount of UV radiation in order to produce vitamin D
Ex. Altitude: people living at higher altitudes have evolved genetic variants that allow them to thrive despite the low
levels of oxygen
Ex. Local pathogens: people have evolved a genetic resistance to pathogens that are more present in their
environment
Cultural factors also influence genomic variation
-Humans are a product of culture-gene co-evolutions: have evolved biological predispositions to depend on cultural
information, and this cultural information enhances their fitness as it continues to evolve
•Also, as their cultures continues to evolve, it places new selective pressures on the genome, which evolves
accordingly
-Ex. Two domestication has led to the development of a mutation that allows us to process milk (lactose tolerance/
lactase persistence)
•Normally people lost the ability to digest milk after childhood (once you stop breastfeeding)
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November 22, 2017
-Lactase is no longer expressed (lactose intolerance/lactase nonpersistence)
•With cow domestication as a cultural practice, milk was readily available across the lifespan
•In places with cow domestication, the ability to digest milk was retained across the lifespan
-Lactase continues to be expressed due to genetic mutation
-This gene became more prevalent because those who could digest the milk had a survival advantage since
they had another source of nutrients
-Ex. Yam farming in Africa and malaria resistance
•Required the cleaning of forests —> standing pools of water —> malaria-carrying mosquitoes
•The cultural practice of yam farming led to the biological adaptation of resistance to malaria
•Linked to the development of sickle cell anemia and heterozygote advantage
Acquired Biological Variability
Moken young children swim underwater to retrieve seafood
-They have thus developed twice the underwater visual acuity as European children
-They have learned to constrict their pupils differently in order to be able to see better underwater
•NB: not due to genetic differences, due to practice
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Obesity: obesity rates have been rising and rising too quickly to be attributed to genetic evolution, so it is likely that
cultural changes over time have caused this increase
-Some explanations include:
•Greater reliance on high-calorie foods (ex. Fast foods, sodas)
•Larger portion sizes
•More sedentary lifestyle
•Suburban lifestyle - more driving, less exercise
-Within the West, there is considerable variation in obesity rates
-Ex. France has one-fifth the obesity rate of the United States
•This is despite French food being high in fat and sugars
•French have higher blood cholesterol than Americans but less heart disease
•French still eat significantly less calories a day than Americans
Normal pupil
Moken pupil
under water
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