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Lecture 6

Biology-Lecture 6-Chapter 11-Human Variation Oct 16 2008

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Marcel Danesi

Reading Notes 10-16-08 Chapter 11: Human Variation Processes in Human Variation O Directional Selection: a type of natural selection that increases the frequency of a trait (the trait is said to be positively favored, or adaptive) O Normalizing Selection: the type of natural selection that removes harmful genes that arose by mutation O Balancing Selection: a type of selection that occurs when a heterozygous combination of alleles is positively favored even though a homozygous combination is disfavored O Natural selection does not account for variation in frequencies of neutral traits O Similar frequencies of neutral traits in human populations may result, then, from genetic drift or gene flow Natural Selection O Natural selection may favour certain genes because of certain physical environmental conditions, as in the case of the moths in England (darklight moths- industrialization-> newly darkened trees; predators could not see dark moths= soon outnumbered light moths) Influence of the Physical Environment O Physical environment can sometimes produce variation even in the absence of genetic change O Climate: influences body growthdevelopment O Acclimatization: impermanent physiological changes that people make when they encounter a new environment O Ex: when we are cold-> our bodies attempt to make heat by making our muscles work: shivering O Longer exposure to cold= increase interior bodily temperature Influence of the Cultural Environment O Humans can dramatically affect their environments O Cold= living in house, harnessing energy to create heat, wearing clothing etc Biological Diversity in Human Populations O Adaption: basic biocultural flexibility of humans responding to their environment Body Build and Facial Construction O Body build of many birds and mammals may vary according the temperature of the environment in which they live O Bergmanns Rule: the rule that smaller-sized subpopulations of species inhabit the warmer parts of its geographic range and larger-sized subpopulations the cooler areas O Relationship between body size and temperature: the more slender population of species inhabit the warmer parts of its geographic range, and the robust populations inhabit the cooler areas O Allens Rule: the rule that protruding body parts (particularly arms and legs) are relatively shorter in the cooler areas of a species range than in the warmer areas O long limbed, lean body type: often found in equatorial regions provides more surface area in relation to body mass and thus facilitates the dissipation of body heat O Shorter limbed body type: found among residents of cold regions promotes retention of body heat because the surface area relative to body mass is less O Facial structure may also be affected by the environment O Risenfield: Facial width of rats increased in cold temperatures and their nasal openings grew
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