ANTH 1120 Lecture Notes - Thrifty Gene Hypothesis, Lactase Persistence, Vitamin D Deficiency

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Contemporary Human Diversity
1. Concept of “race”: a social construct not biologically valid
2. Relationships between evolutionary processes and cultural-environmental
3. Adaptive significance of human variation
4. As we change/evolve, so do other organisms
Mutations and genetic variation
Natural selection
Polymorphisms: main focus of human variation studies (2 or more alleles)
How adaptive a gene/trait is depends on the environment
Dark moths and light moths in industrial England
Types of natural selection
Directional selection: a particular trait seems to be positively favoured;
average values shift over time
Normalizing selection: the average values do not change, but extremes
Birth weight-
Balancing selection: when a heterozygous combination of alleles is positively
favoured even though a homozygous combination is disfavoured
Sickle cell allele
Race: social construct, biological fallacy
Humans classify things (order world around us)
Classifications are not necessarily without bias
Linking physical traits with behavioural traits
Overlooks complexities (such as culture)
Draws on the biases of the classifier
Classifications can be essentializing , typological
Racial classifications: product of social/cultural beliefs re:
Historical and contemporary discrimination
anthropologists : concept of “race” cannot be applied to human variation
AAPA (quote (pg.228)
Different populations not clearly classifiable by discrete traits
For example: skin tone
No clear breaks between skin tones and no other physical traits that
correspond with skin tones at all times
Also: epicanthic fold (pg. 233)
No single group of traits always applies to a group of people all the time
there is variation within “groups”
Amount of genetic variation accounted for by differences between
groups is less than variation that exists within groups
The point?
Human are a polytypic species
Biological traits show clines
Clines: gradual differences, rather than sharp, discrete differences, for
Skin tone
Nose shape
“race” classifications attempt to make clear boundaries where they aren’t
any (and are therefore divisive)
We can ask:
If race is not a useful device for classifying humans, why is it so widely used
Ideas of “biological determinism”
The (incorrect) belief that there is an association between physical
characteristics and intelligence, behaviours, morals, values, abilities, social
and economic status
Makes it possible to persecute others (a justification used to
perpetuate inequalities)
Historical examples
Biological determinism
Incorrect, but still prevalent today in various forms
So-called “research” that links ideas of intelligence and behaviours of 3
Evolutionary Processs + Adaptive significance
Some human diversity not just due to physical stressors like UV radiation
Also part of a response to the environment we have modified with our
own actions
Biology shapes culture and vice versa
Malaria, sickle-cell allele and the rise/spread of agriculture in Africa
Mosquito breeding grounds, parasite spreads
Malaria as “a powerful selective force”
Another aspect to malaria
– Food:
Traditional crops: cassava, millet, sorghum, can sugar, dark lima beans
Contain cyanate and thiocyanate, which seem to inhibit the sickling of
red blood cells- might reduce the symptoms of sickle cell anemia
Dietary changes thus can affect the sickle-cell situation
Lactase persistence (continued production of lactase enzyme after childhood;
allows milk digestion)
Pastoralism and dependence on herd animals and milk changes in
the frequency of the lactase-persistent allele (selective pressure)
The point?
Our actions, decisions, shape environment around us, and can also shape our
A dialectic
Dialectic: dynamic tension within a given system and the process by
which change occurs on the basis of that tension
Human variation + adaptive significance
Physical stressors
Extreme cold, extreme heat, UV radiation…
Adapting to different environments
Variations in skin tone- why adaptive (advantageous)?
First discussed in terms of exposure to solar radiation
Darker tones closer to the equator greater protection against skin
Vitamin D
Liver, fish oils, butter, yolks, cream
But can be produced by body too through exposure to UV radiation
UV radiation weaker further from equator lighter skin would be
advantageous in these regions
Rickets- vitamin D deficiency- larger forehead, wide bones, large
abdomen, odd shaped legs
Folate degradation
Folate: important in fetal neural tube development
Neural tube: the anatomical structure that forms brain and
spinal cord
Must be protected by bone
Spina bifida
Folate susceptible to degradation by UV radiation
Darker skin would offer some more protection (a selective
advantage closer to Equator)