october 27th

October 27 2011 ANTHRO*1120 Contemporary Human Diversity 1. Concept of “race”: a social construct  not biologically valid 2. Relationships between evolutionary processes and cultural-environmental contexts 3. Adaptive significance of human variation 4. As we change/evolve, so do other organisms Reminder: – 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 removed ○ 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: inferiority/superiority ○ Historical and contemporary discrimination – anthropologists : concept of “race” cannot be applied to human variation – AAPA (quote (pg.228) Why? – 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) Thus – 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 example:  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 today? 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 ○ Racism ○ So-called “research” that links ideas of intelligence and behaviours of 3 “races” 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 Examples – 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 Examples: – 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 biology – 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  Altitudes 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 cancers – 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) A word of caution re: thrifty gene hypothesis (pg. 243-244) – Idea ○ Genetic change to store calories better- insulation against feast- famine cycles – Critiques ○ Cultural variation in the past ○ Severe famines rare; more deaths tend to come from disease, not starvation ○ Clear evidence of thrifty genes and what they do not yet discovered ○ Contemporary changes: costs of healthy food vs high-fat, high sugar food in isolated areas; changes in activity patterns – Seasonal change on yearly basi