Chapter 16.docx

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University of Toronto Mississauga
Esteban Parra

Chapter 16 – Human adaptation Adaptation = successful interaction between population + environment - stress = any factor that interferes with the normal limits of an organism being able to operate - organisms maintain normal limits of body functioning through homeostasis - - thus adaptations restore homestassis, as a way of dealing with stress that can change body functioning - when we adapt to stresses, we may be introducing new stress: like pollution – - there is an interaction between levels: physiologic, developmental, genetic – ex. Medical treats people – but may lead to larger pop sizes = thus food shortage = more stress Other forms of adaptation = acclimation, acclimatization, developmental acclimatization 1) acclimation = short term changes that occurs very quickly after being exposed to a stress – ex. Sweating if u are hot 2) acclimatization = physiological changes that take longer – ex. Increase in red blood cell production (when moving to a high altitude environment) - 3) developmental acclimatization – if a change occurs during the physical growth of an organism - changes in organ or body structure ( ex. Increase in chest size when person grows up in high altitude) *plasticity = ability of organisms to respond phsyiologicall or developmentally to environmental stresses = plasticity Climate and human adaptation - we have been able to expand to many parts of the environment because we have developed adaptations to many temperatures around the world Physiologic responses to temperature stress - we can maintain constant body temp because we are warm blooded Cold stress - Example of acclimation: - when we’re cold, we lose a lot of heat very quickly - thus we may increase heat production by shivering, which also increases metabolic rate - or minimize heat loss by constriction and dilation of blood vessels - vasoconstriction: narrowing blood vessels, to reduce blood flow and heat loss - vasodilation: opening blood vessels, to increase blood flow and heat loss *both need to occur to keep balance between heat loss and damage to extremities (ie if vasoconstriction occurs, less blood flows to extremities – but if this happens for too long, this can be dangerous – therefore vasodilation occurs where heat flows from interior of the body to extremities – but this means body loses heat - thus u need a balance - how- the cycle of constriction and dilation levels out, thus it becomes more frequent and less extreme changes - = Lewis hunting phenomenon – Heat stress - heat is not being removed quickly enough - 4 ways that heat can be lost: - 3 ways also increase heat – evaporation doesn’t 1) radiation: heat flow from objects (in electromagnetic radiation) - thus the body removes radiation but also picks it up by other objects 2) convection: removal or gain of heat through air molecules – heat flows from warm to cool object 3) conduction – heat exchange through physical contact with another object – ex. Ground or clothes ***accounts for small amount of heat exchange 4) evaporation – loss of heat through conversion of water to vapour - *heat loss depends on temperature and humidity: - if temp increases, then evaporation increases – But if temp is fairly stable, heat removal occurs through radiation - vasodilation also helps remove heat – opening blood vessels – then heat is lost through 1 2 or 4 *heat evaporation is difficult under hot and humid conditions – better in hot and dry conditions Climate and morphological variation - size and shape of body and head affect peoples ability to handle temperature stress: nose size and shape are related to temp and humidity - Bergmann and allen rules - there Is a relationship between average body size and temp – people in cold temp are heavy and people in warm climates are light - Bergmann – explained this in terms of physiology and heat loss: - his rule: mammals that are similar shape, the larger mammal will lose heat slowly thus be better for cold environments, whereas the small mammal will lose heat quickly thus be better for warm environments - why? Heat loss is based on total surface area But heat production is based on total volume - a large mammal has greater surface area and volume – BUT the ratio of surface area to volume is less – thus the larger the animal, the slower the rate of heat loss (because theres such a large volume but heat can only escape through one door since theres small amount of SA) – analogy *Bergmanns rule also deals with body shape: mammals with a more linear body shape lose heat more quickly and are better adapted to hot climates – but mammals whos body shape is less linear and more stocky lose heat less rapidly – and are better adapted to cold environments Allens rule = mammals in cold climates have shorter, bulkier limbs – allowing less loss of body heat – whereas mammals in hot climates have long, slender limbs – allowing greater loss of body heat - Body size and shape - do these rules also apply to humans? - yes - but there are still variations within populations - but in general, inuits are shorter, stocker build (for cold environment) but – Africans are taller and thinner (for hot climates) - evidence shows that genetic and environmental factors influence relationship between climate, growth, body size and body shape - if children grow up in a climate different from their ancestors, they grow in ways the indigenous children do - nutrition also influences it – Health care and nutrition have made these associations less strict - Cranial size and shape - in the past, this was the focus of racial classification - but Retzius developed a measure of cranial shape called cephalic index: a measure of cranial shape – It is the maximum width of the skull divided by the maximum length of the skull x 100 – to get a % - answer means – that the persons head width is almost ___ of the head length - in human populations, it ranges from 70-90 - cant use these to rep racial classifications – like they did in the past - found a relationship between cranial shape and climate – pop in colder climates had wider skulls compared to length – IN RELATION to people in hot climates *average cephalic index was larger for those in winter frost - the shape of the upper part of the skull is related to heat loss – rounded heads (high cephalic index) – bigger width – lose heat slowly – and are better for cold environments - narrow heads (smaller width) – lose heat quickly – better for warm environments Nasal size and shape - has a relationship t
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