modern human variation

linneaus

classified 4 human subspecies based on skin color corresponding to american, european, asian and african

craniometry

measurement of the skull

craniometry claims that..

skull size is correlated with intelligence

phrenology

shape and contours of skull reveal talents and abilities

social darwinism

physical traits used to “justify” discrimination

lombroso: criminal anthropology

idea that criminals are born that way

atavism

evolutionary “primitive” traits occasionally reappear

• criminals are apes

eugenics timeframe

late 1800s, early 1900s

eugenics basic idea

society’s problems can be solved by controlling the gene pool and removing “undesirables”

eugenics results

lead to people being sterilized

4 problems with eugenics

1. reification: labels are not meaningful

2. arbitrariness: who decides who is fit?

3. hereditarianism: assumes all behaviors are genetic

4. superiority: fitness is time dependent/changing

reification

representing something abstract as a “thing” ex intelligence

race as a biological concept

geographically defined, genetically differentiated population

race as a biological concept is equivalent to…

subspecies

does race have biological meaning for humans/does homo sapiens have subspecies?

no

IF humans were biologically divided into races, we would expect to see:

• biological variation across geographic regions

• biologically distinct populations

  • easily identifiable groups with minimal gene flow between them

  • the biological differences between groups are NOT solely adaptive

can we identify distinct groups among humans?

• no because…

• little agreement due to poorly defined “races”

• geographic variation is not discrete

• independent variation of traits— no patterns

myth of the primitive isolate

at some point early in our species history, there were isolated, pristine populations of “pure” races that did not interbreed, and that races today descended from these ancient races

reality of early homo sapiens

small, highly nomadic groups with lots of migration and gene flow

genetic data

more genetic variation within “traditional” races or populations than between them— traditional race divisions explain only 6-10% of all genetic variation found within humans

most of the traits that we attempt to use to define race actually reflect…

functional adaptation

_____ can create people with similar traits in different parts of the world that have similar climate

convergent evolution

traits resulting from convergent evolution

• head shape

• nose shape

• body build

• skin color

do we see genetic variation across geographic regions?

yes BUT the concept of race does NOT explain human biological variation

allen’s rule

animals in cold climates tend to have large, stout bodies while those in hot climates have long, thin bodies (both within and between species)

allen’s rule thin body

more surface area = more area for animal to lose/dissipate heat

allen’s rule stout body

better at conserving heat

can allen’s rule be applied to humans?

yes:

• populations adapted to colder climates ex arctic circle = short, stout body = better at conserving heat

• populations in equatorial, tropical, arid environments that are exposed to high temperatures = lean, linear body build = dissipate heat more effectively

2 main sources of biological variation among humans

• acclimatization

• adaptation

acclimatization

short term changes that reflect responses to specific environmental conditions manifested within an individual person

adaptation

results from changes in allele frequencies manifested at the population level

vasoconstriction

blood vessels at skin constrict, reducing blood flow to the surface to restrict heat loss and conserve energy

skin color

the ability of the body to produce melanin has to do with the number of melanin-producing cells called melanocytes as well as the amount of melanin in each melanocyte

individuals that are darkly pigmented have a ____ ____ of melanocytes in the skin

high density

high sun exposure ___ melanin production capabilities

increases

melanins effect with sun exposure

blocks UVB from the sun, which can cause skin cancer and destroy sweat glands

rickets

bone disease due to vitamin d deficiency

people living in areas with less intense sun exposure that have evolved lighter skin is an example of ____

adaptation

people that tan due to increased sun exposure is an example of ___

acclimatization

most (visible) human biological variation can be explained using aspects of ___ and ____

adaptation, evolution

adaptations that explain human biological variation

• temperature

• altitude

• sun exposure

the variation that some have tried to attribute to biological race is the result of ____ rather than ____

adaptation to the environment, long-term isolation