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Health Studies
R Song

Lecture 4: Variations in Human Growth and Development January 30, 2012  Humans: 99.9% identical at DNA sequence level (o.1%) difference o Chimps: 2-3x different o Orang-utans: 8-10x  Genotype: DNA sequence level of comparison o Genetic blueprint  Phenotype: physical manifestation of your genes o How you look like is the expression of genes, eg. Height  Rwanda: Tutsi, Hutu, Twa o Within these groups, there’s variations; height Comparative Growth (children/ adolescence) 1. Skeletal Measures (height, proportions) 2. Dental Development (eruption) 3. Body Composition/ Weight (fat, muscle) 4. Sexual Maturation (esp. Menarche) 1. Skeletal Measures (height, proportions)  Expected pattern of growth (generalized growth pattern)  Can be variations in how the curves can be stretched horizontally or vertically  Comparison between modern human population  Part of it is genetics and also environment over time  Height is determined by less access to resources to food, greater demands on the body such as labour and b=poor health care or disease  Result of other factors other than genetics, such as culture  Guatemala Maya o Generally shorter o Result of stunting due to poor nutrition o They moved to the US and their height increased by 5 cm  Clear difference, genetic not always the factor to population growth Relative to total height  Value for leg height  Sitting height – standing height  Taller sitting height = shorter legs  Shorter sitting height = longer legs * Quiz: Reduced “sitting height” relative to total height suggests that:  leg length is relatively long Weight for Height  Differences in weight for certain height o E.g. between Africans and Europeans Adolescent Growth in Disadvantaged Populations  Late-maturing kids (i.e., due to earlier G/D interruption, ill health/undernutrition) have reduced peak height velocity (adolescent growth spurt) compared to early-maturing kids  But children with slow growth prior to puberty will have a longer-lasting growth spurt during adolescence than a child who achieves greater pre-pubertal % of adult height o Reduced overall height  Areas of endemic chronic undernutrition, disease, child labour: height at every age is reduced compared with less stressed pops; but TOTAL SPAN of growth period is prolonged o (i.e. up to 25/26 yrs, rather than 18-21 yrs) 2. Dental Development (eruption)  Up to 15 years of age  How far out your teeth are erupted  Help compare population growth  Population Differences o If there is a variation in population and why? o African Americans show advanced growth development of teeth compared to White American 3. Body Composition/ Weight (fat, muscle)  Subcutaneous fat layer o Principle anthropometry measures of arm:  Upper arm length  Triceps skin fold (TSF)  Pinching skin on your back  (mid)-upper arm circumference (M)UAC  How well a kid is growing  Malnourished and undernourished do not have much fat  Triceps skin fold thickness o Measure of extremity fat of the trunk o Fat on your arm  Subscapular skin fold thickness o Fat behind your shoulder blade o Reflection of trunk fat o Less food, fat is concentrated near the trunk for children who are malnourished or undernourished  Inadequate skin fold thickness Diagrams (see above)  Shows how we can look at fat in different populations  Girls, particularly, juvenile stage have more fat than boys  High SES ties in with high body fat  Indigenous Maya have low SES, therefore, less body fat within both genders 4. Sexual Maturation (esp. menarche)  Boys: o Growth of sex organs; pubic/body/facial hair o Voice change o Seminal emissions  Girls: o Growth of breasts, pubic/body hair o Menarche (first menstruation) o Development of internal/external sex organs  Tanner Puberty Stage Classification System See some differences between normal/healthy populations in average timing of onset of stages of adolescent maturation, but generally: more variation within a population than between them o More variations in height and skin colour within population groups than in others o (even severely malnourished infants/kids show normal pattern of secondary sexual development in adolescence)  Can be delayed, take longer to complete Adolescent Girls vs. Boys  Little difference in average stature between boys and girls until adolescence  Girls usually begin adolescent growth spurt about 2 years earlier; thus on average, girls taller than similarly aged boys for a couple years  Boys, once adolescence starts, grow at faster rate  While boys have more muscle mass at all ages, difference from females increases at adolesc
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