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Flashcards in Climate Deck (21)
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What is human variation the result of?

Genetic drift, gene flow, genetic adaptation (through natural selection) to environmental conditions both past and present, physiological and cultural responses


Human plasticity

Includes physiological/cultural responses to environmental changes


Environmental Stress

Environmental Stress is any condition that disturbs the normal functioning of an organism, this eventually disturbs the organism’s homeostasis



Homeostasis is when the body of an organism has a consistent and relatively stable internal environment and is maintained by feedback loops


Common forms of environmental stress

Ultra violet radiation
Heat stress
Humidity Stress
Cold Stress
Nutritional Stress
Disease Stress
Population Pressures


Hot and cold stress

-Both ancient stresses on humans
-Cause less loss of life than malnutrition and disease
-Because humans are better adapted to hot and cold stress


Ideal Internal Core Temperature

37-37.6: ,more than a few degrees either direction from this range is fatal


Ways of adapting to hot and cold stress

Adaptation: Evolutionary change
Accommodation: responses that ensure survival but many have a long term cost
Developmental adjustment: Adjustments to physiology in response to the environment during developmental stages
Acclimatisation (acclimation): gradual, reversible adjustments in response to changes in environments
Behavioural/Cultural responses: responses that are learnt and culturally and environmentally specific e.g wearing warm clothing or sun cream


How can the body heat up when cold?

1. Increased metabolism
-exercise or shivering
-hormone-induces increase in metabolism
-infection (i.e. fever)
2. Non-shivering thermogenesis (induced by hormones)
3. Conduction (touching hot things)
4. Convection (contact with hot air)
5. Radiation (receiving infrared waves)


What increases your risk of freezing to death

-Highest mortality rate in infants, the elderly, the poor, alcoholics and those who are in water


What else can help warm you up?

-Subcutaneous fat (developmental adjustment?)
-Muscle (developmental adjustment?)
-Avoiding cold (behavioural/cultural response)
-Wearing protective clothes (behavioural/cultural response)
-Favourable body proportions (developmental adjustment)
-Higher resting metabolic rate (adaptation, behavioural response)
-Lower core temp, delayed shivering, increased non-shiveering thermogenesis (acclimatisation-within 5-10 days)
-Hunters waves (adaptation, accommodation?)
-Protruding, narrow nose (adaptation)


Body Proportions

Bergmann's Rule (1847)
-People closer to the equator are less bulky than people who live in cold areas
Allen's rule (1877)
-People closer to the equator have longer limbs than people who live in cold areas


What increases your risk of heating to death

Infants, elderly, the poor, elite athletes, workers


Heat and metabolism

Humans produce a lot of heat constantly through metabolism, whether exercising or not
This means when core body temperature is high, physical activity adds stress (the opposite of what happens with cold exposure)


Responses to heat

Involves vasodilation, conduction, radiation, evaporation and behaviour/culture
1. Internal heat moves by conductance and vasdilation to the body surface where it can radiate away
2. Sweat glands produce sweat which evaporates to cool the skin (more difficult in humid climates)
3. Ventilation
4. Early/Late working and siestas
5. Clothing styles


Heat Acclimatisation (7 days-8 weeks)

1. Increased plasma and blood volume
2.Low sodium sweat
3. Lower threshold for sweating and vasodilation
4.Reduced heart rate (with more efficient beating)
5. Reduced metabolic rate
6. Re-absorption of sweat
7. Lower core temperature
8. Recognising when to stop


High Altitude

-Considered 2500 meters and higher above sea level
-At these altitudes there is lower barometric pressure, leading to fewer oxygen molecules per breath
-Hence, hypobaric hypoxia
-Reduced oxygen in air and reduced ability to get oxygen from the air
-33% of the oxygen at sea level is at the top of mount Everest
-Highest point of human habitation has 55% of the oxygen that there is at sea level


Illness related to altitude

Acute mountain sickness:
-usually visitors
-headache, nausea, vomiting, anorexia, fatigue, breathlessness
-sometimes pulmonary edema and cerebral edema
Chronic mountain sickness
-can happen to people who are well-adapted and long-staying at high altitudes
-headache, dizziness, tinnitus, breathlessness, palpitations, sleep disturbance, fatigue, anorexia, mental confusion, cyanosis, and dilation of veins
-bone marrow produces too many red blood cells, level of oxygen in blood low


Altitude Acclimatisation

-Hypoxic ventilatory response - breathing becomes deeper and faster (temporary)
Increased concentration of haemoglobin in the blood
-higher heart rate (temporary)
-Inactive capillaries open
-Tissues in lungs more full of blood
Athletes are more negatively affected and cannot resume physical work capacities as quickly as others


Altitude Adaptation

-Higher resting ventilation rates
-Larger lung volumes
-elevated haemoglobin levels
-Fetal oxygen transport improvements in the placenta
-Greater uterine artery blood flow
-Shorter stature?
-Larger chest dimensions?


High altitude Tibetans

Ethnic Tibetans possess heritable adaptations to low oxygen availability
-high oxygen saturation of blood (associated with red blood cell production) but no IUGR or foetal mortality (due to blood viscosity)
-One single-nucleotide polymorphism associated with red blood cell production
-Shows a 78% frequency difference between Tibetan and Han Chinese samples, who only diverged c3000 years ago
-Faster rate than the spread of lactose tolerance in northern Europe, which took 7500 years