ANP causes human diversity_15

patterns of variation

within a population

• frequencies of phenotypes, genotypes alleles

ex. blood type

between populations

• the geographical pattern of frequencies

cline

gradual phenotypic change (= gradual change in allele frequencies)

discontinuous distribution

little or no gradation in phenotypic change

causes of genetic variation

individual variation (between individuals)

- alleles inherited from parents

genetic variation within/between populations

- mutation, gene flow, genetic drift

- Natural selection is often caused by environmental variation (incl. variation in culture

precondition for natural selection

inheritance

- heritable traits are passed on to offspring

genetic variation

- traits vary between individuals

environmental pressure

- filter which selects advantageous traits

→ results(natural selection)

- individuals with advantageous traits survive better and have more offspring

- advantageous traits will be more common in the next generation (more individuals have the traits)

Environmental stressor: disease

sickle cell disease

• autosomal recessive traits

environmental stressor: novel food

red indicates high lactase persistence

environmental stressors

behavioral responses

environmental stress → behavioral response

• behavioral adjustment

• short-term, cultural

→ almost no change in phenotype

• different cultural solutions may affect the phenotype

individual (single generation)

- biological plasticity

= acclimations which is short-term phenotypic change that's reversible

= Adaptability is the developmental effects on phenotype; not reversible

over many generations

- natural selection leads to adaptation

- genetic fitness variation

→ together produce phenotypic variation

effects of environmental stressors

natural selection

- different environments may favor different traits

- Gene flow tends to homogenize populations

- If the selection is strong enough, genetic differences between populations will be maintained

examples of natural selection and genetic variation among human groups

- effects of heat and cold stress

- effects of the sun

- effects of high altitude

body size and shape

vary with climate

• adaptation to cold and heat

animals

• in cold places are large, stocky

• in hot places are small, thin

bergmanns rule

larger animals (have less relative surface area and) lose heat less rapidly than small mammals

animals

- in cold places are large, stocky, with short limbs

- in hot places are small, thin, longer-limbed

allens rule

mammals in cold environments have shorter, bulkier limbs, in warmer environments thinner longer limbs

same principle for modern humans

skin color

hemoglobin - red blood cells

carotene - yellowish pigment and the top layer of the skin (epidermis)

melanin - red/dark brown pigment

basal layer in the skin. produced by melanocytes and triggered by UVB

- absorbed UV and protects

a similar number of melanocytes but differences in..

- rate of melanin production

- size of melanin particles

- location melanin in cell

geographical distribution of skin color

• clinal distribution; darker at equator

glogers rule

Within the same species, there is a tendency for the more heavily pigmented populations to be located near the equator and the lighter populations farther from the equator

effects of UV rays

harmful

- damage DNA - skin cancer

- destroy folate (vitamin B) - neural tube defects

beneficial

- vitamin B synthesis

- calcium absorption; rickets

- immune function

synthesis of pre-vitamin D3

for humans with lightly pigmented skin

UV stress and responses

behavioral adjustment

- clothing; sunscreen lotion

acclimatization - tanning

skin color as an adaptation

1. near the equator - more UV radiation

- dark skin protects against skin cancer and folate destruction

2. northern latitude - less UV radiation

- light skin for better vitamin D production supports bone growth and a healthy immune system

additional skin color variation

within a geographic area

- long-term residents - darker or lighter (depending on latitude}

- more clothing - lighter

- gender - women usually lighter than men

skin color

neanderthals

- ca. 300-30 ka B.P.

- Europe

first Homo sapiens

- ca. 200 ka B.P.

high altitude environment

- partial oxygen pressure reduced with increasing height

- humans affect starting at ca. 5,000 ft

—hypoxia

- reduced oxygen saturation of hemoglobin

- reduced oxygen transport to tissue

—altitude sickness

- headache, nausea, etc, (above ca. 8000 ft)

- high altitude edema (above ca. 11,500 ft)

reponses to lack of oxygen (1)

behavioral adjustment

- change to the environment

- e..g.. airplanes pressurized

- increases breathing and heart rate, more inactive

acclimatization

- increases the number of red blood cells

responses to lack of oxygen (2)

adaptations

- reduced oxygen consumption

mechanisms

- increases the amount of hemoglobin

—Andean populations

- less hemoglobin, but more effective oxygen use including,

- Tibetan populations

- gene variant from Denisovans

→ different adaptations

conclusion: human biological diversity

often environmental adaptations

- important to our survival

not fixed characteristics

- have changed; are changing; will change

variation between groups

result of

- mutation, natural selection, and genetic drift

differences reduced

- gene flow

learning objectives