Chapter 15 - Race and Human Variation

Linnaes’ Four Races of Huamns

categorized humans into 4 races

Johann Blumenbach’s

took Linneas’ classification and instead classified races into 5

• also based his categories on skull shapes

• also stated it is impossible to categorize humans into races properly because humans have so much diversity in appearance

  • there is variation but it exists as a gradient, not as categories

Historical views of human variation

• there was ethnocentric bias

• Darwin’s new theory of natural selection lead people to realize that physical traits (and behaviour and intelligence) could be inherited

• assumed that if other races had “primitive” technology and customs, they must not be evolved enough for modern civilization

• biological determinism

Ethnocentric bias

refers to how white Europeans were the ones doing the classifying and they invariably ranked themselves as the best among the races

biological determinism

idea that a population’s cultural and technological abilities are biologically inherited

TRUE OR FALSE: Darwin’s theory about inheritance of traits was the beginning of people’s thinking about breeding

FALSE

• Europeans understood breeding long before Darwin’s theory

Eugenics

the selective breeding of humans to improve the human species

• was widely supported by western civilization in the late 19th / early 20th centuries

Looksmaxxing

considered Modern Day Eugenics

• states that there is only 1 type of attractive guy

History of Eugenics

• was taken to the extreme in a Nazi-occupied Europe

• became less popular after the holocaust

  • but didn’t fully go away

  • ex. Eugenics in Canada

    • sterilization programs for minorities, especially First Nations until the 1970s

The fantasy of Race

• We make up popular culture (about race) to understand our real world culture

• then we consume popular culture (about race) which we apply into the real world

Race

is a fiction humans have written and continue to write

• it is a social construct

• does not reflect biological reality

• relies on phenotypic traits

• in reality, humans cannot simply be divided into categories based on shared biological traits (like in species)

Is there more genetic variation between populations?

no, there is more genetic variation within populations than between populations

• we have more common in between populations than with individuals within populations

What can you say about this global map of Indigenous skin colours

Darker coloured skin coloured populations are closer to the equator

• are more exposed to sunlight

Humans as a Polytypic species

Humans are a Polytypic species

• all contemporary humans are members of the same polytypic species, Homo sapiens

• even local populations have genotypic and phenotypic variation between individuals

Polytypic spcies

composed of local populations that differ in the expression of one or more traits

Polymorphisms

characteristics with different phenotypic expressions

• a genetic trait is polymorphic if the locus that governs it has two or more alleles

• geneticists use polymorphisms as a tool to understand evolutionary processes in modern populations

Cline

gradual change in the frequency of a trait or allele in populations dispersed over geographical space

Clinal distribution

reflects natural selection and gene flow

• caused by evolution

  • explained in evolutionary terms

• does not reflect racial boundaries

How do we classify people today

• Nationality - what country you come from/live in

• ethnicity - traditional culture group

• ancestry - biological population your ancestors came from

• race - a poorly defined social construction that includes aspects of all 3

Is the term “race” useless?

No, we cannot ignore this term because that would mean ignoring the harm it causes

• BUT we must understand what it really means

• most important thing to remember is that biology cannot be used to divide people into categories

2 levels of physiological response to the environment

1. Long term - Adaptation: evoltionary change which makes population better-suited to its environment

2. short-term - Acclimatization: temporary physiological response

Homeostasis

the balance that allows living things to be systems of cooperating functions

Stress

the body’s response to environmental factors that throw homeostasis off balance

• it is an attempt to regain homeostasis

• acclimatization responses help individual organisms maintain homeostasis even if if there are fluctuating environmental factors

Ulraviolet rays

penetrate the skin and can eventually damage DNA within skin cells

• 3 major types of cells that can be affected:

  • squamous cells

  • basal cells

  • melanocytes

advantages of dark skin

• reduces risk of sunburn

• protects from folate degradation (especially important for pregnant for mothers)

Why doesn’t everyone have dark skin?

• process of Vitamin D synthesis in the skin needs sunlight

• harder for people living up north to reach sunlight

• insufficient amounts of vitamin D during childhood results in rickets

  • rickets - condition often leading to bowing of the long bones of the legs and deformation of the pelvis

Sunlight and acclimatization

humans populations adapt to sunlight levels through changes in skin colour

• individuals acclimatize to sunlight by changing skin colour by tanning (short term)

  • in the sunny seasons, exposure to sunlight stimulates melanocytes to produce more melanin

  • in the winter, tans fade away and allows individuals to absorb more sunlight and produce more vitamin D

is tanning an acclimatization or an adaptation

• Tanning - acclimatization

• ability to tan - adaptation

  • trait that humans evolved through natural selection

Thermal environment of animals

• mammals and birds - evolved complex physiological mechanisms to maintain a constant body temp

• most mammals won’t survive temperatures that differ from 37^C by only a few degrees, even for only a few hours

• humans can range from 50^C to -50^C

Long-term adaptations to heat that our ancestors evolved

• sweat glands

• vasolidation

• limb proportions

• body size

Adaptations to temperature

• Allen’s rule - populations in colder areas tend to have larger bodies

• Bergmann’s rule - populations in colder areas tend to have shorter limbs

• based on the laws of thermodynamics - ratio of surface area to volume

Acclimatizations to temperature

short-term responses to cold:

• First response - shivering

• metabolic rate increases to produce more body heat

• vasoconstriction - narrowing of blood vessels

  • reduces blood flow from the skin and preserves core body heat

• vasodilation - widening of blood vessels

  • to warm peripheries and prevent frostbite

    • don’t drink alcohol to keep warm in a survival situation

High altitude population adaptations

have adaptations that influence lung volume and red blood cell production

How can lowlanders acclimatize to high altitude

• immediately hyperventilating

• after a period of time, the body can adjust by increasing red blood cell production

Infectious diseases

caused by invading organisms such as bacteria, viruses, or fungi

• throughout evolution, disease has exerted selective pressures on human populations

• disease influences the frequency of certain alleles that affect immune response

impact of infectious diseases

• humans and pathogens exert selective pressures on each other

• microorganisms evolve

• a pathogen must not be so virulent so it doesnt kill its host too quickly

• selection acts to produce resistance in host populations and/or to reduce the virulence of disease organisms

Malaria

blood-borne pathogen spread to humans through mosquitos

• may be the single greatest cause of death in human history

• strong selective pressure

sickle cell disease

autosomal recessive disease which causes anemia (red blood cell deficiency)

• affects hemoglobin gene

• selective pressure

  • anemia is dangerous and can result in a greater risk of early death

Hemoglobin gene

protein in blood cells which transports oxygen

connection between heterozygotes and malaria vs. anemia

• Hb S homozygotes are at risk of anemia

• Hb A homozygotes are at risk of malaria

• heterozygotes carry the mutated recessive allele, but it is not expressed so they do not get sickle cell disease

  • because you need 2 alleles to get SCD

• heterozygotes are favoured as they are resistant to SCD but are also less likely to get anemia

Heterozygote advantage

alters trait expression in a subtle way which makes carriers immune to diseases, even if the trait is not expressed

• ex. can cause carriers to be immune to malarial infection