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Lecture 21 - Modern Human Biology Adaptation - March 19.docx

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University of Toronto St. George
Keriann Mc Googan

March 19, 2013. Lecture 21 - Modern Human Biology: Adaptation Planet Madagascar: A World in an Island  Conservation education project  Madagascar has a massive need for conservation  Aimed at developing a community that works towards preserving Madagascar’s biological diversity and improving the quality of lives of people who live there  Home to the world’s smallest lizard; tiny chameleon that is as large as the end of a match o Also lots of geckos o Lots of crazy bugs; giraffe neck beetle o Net throwing spiders  Lemurs o Only found in Madagascar o Over 100 species o Very approachable, not scared of people  Not good from a conservation point of view o Can leap 8-10 metres between trees Adaptive Significance of Human Variation  Adaptation: process of adjustment and change in an organism that enables it to survive and reproduce  Phenotypic plasticity: observable biological changes cause by the environment  Human adaptability describes the study of the basic biological flexibility of human populations o Outside environment = macroenvironment o Artificial environment = microenvironment  E.g. Temperature  We simulate sub-tropical environments with central heating and warm clothes Deeply-pigmented Skin  Skin colour influenced by hemoglobin, carotene, melanin  Melanin: granular substance produced by cells called melanocytes located in outer layer of the skin o Acts as built-in sunscreen o Exposure to sunlight will increase amount of melanin in skin, causing it to darken o Worldwide UV radiation parallel to worldwide skin colour distribution  What causes deeply pigmented skin in the tropics? o 1. People with darker pigmented skin less susceptible to skin cancers and sunburn  1. Early humans lived in the tropics  2. Early humans spent most of their time outside  3. No clothing or sunscreen o SO: UV radiation selected for maximum levels of melanin in early hominins o BUT cancers usually occur AFTER reproduction  i.e. doesn’t affect passing on of genes o 2. Reduce changes of severe sunburn  Very dangerous to the very young, makes body temperature regulation more difficult o 3. Protect against the degradation of folate  Folate: B vitamin, not stored in the body; need to replenish folate through dietary sources  Risk in pregnant women Less-pigmented Skin  Northern latitudes – colder temperatures and cloudy skies  1. Selective pressure for dark skin relaxed  2. Vitamin D hypothesis o Depigmentation related to need for vitamin D o Lack of vitamin D  rickets (disease affecting bone development in children, often don’t reach reproductive stages; women who do have narrowed hips hindering reproduction) The Thermal Environment  Human beings must adapt to temperature extremes  Responses to Heat o Hot-dry environments  Little natural shade  Limited food and water  Cold temperatures at night  Ancestral hominins likely lived in hot-dry conditions  Biological Responses to hot-dry environment  Releasing heat from core of body o Body size increases as distance from equator increases o Bergman’s Rule: body mass increases in colder climates  As mass increases surface area becomes proportionately smaller  Bigger mass to retain heat, less surface area to release heat o Allen’s Rule: shorter appendages more adaptive because effectively reducing exposed surface area and preventing heat loss  People in hot-dry environments have a tall, lanky body type  ….  Sweating o Eccrine sweat glands in humans o Other animals: apocrine sweat glands o Evaporative cooling  Cultural Adaptations to Hot-Dry Conditions  Activity scheduling o Work during morning and evening, mid-afternoon gap/break (like siesta)  Housing  Clothing o Minimal  Shading o Warm-Humid Environments  Solar radiative heat less during the day and night  Reduced variation in diurnal temperatures  Biological responses to warm-humid environments  Similar to hot-dry environments o Vasodilation o Sweating  BUT evaporation of sweat slower, so reduced…  ….  Cultural responses to warm-humid environments  Limited cultural and behavioural adaptations  Clothing minimal  Housing promote air circulation  Responses to Cold o Insulative adaptations  Body size and form (Bergmann’s and Allen’s rules)  Subcutaneous fat
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