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

26 views4 pages
Published on 23 Aug 2010
School
UTSG
Department
Anthropology
Course
ANT100Y1
Professor
Reading Notes
10-16-08
Chapter 11: Human Variation
Processes in Human Variation
y Directional Selection: a type of natural selection that increases the frequency of a trait (the
trait is said to be positively favored, or adaptive)
y Normalizing Selection: the type of natural selection that removes harmful genes that arose by
mutation
y Balancing Selection: a type of selection that occurs when a heterozygous combination of
alleles is positively favored even though a homozygous combination is disfavored
y Natural selection does not account for variation in frequencies of neutral traits
y Similar frequencies of neutral traits in human populations may result, then, from genetic drift
or gene flow
Natural Selection
y Natural selection may favour certain genes because of certain physical environmental
conditions, as in the case of the moths in England (dark/light moths- industrialization->
newly darkened trees; predators could not see dark moths= soon outnumbered light moths)
Influence of the Physical Environment
y Physical environment can sometimes produce variation even in the absence of genetic
change
y Climate: influences body growth/development
y Acclimatization: impermanent physiological changes that people make when they encounter
a new environment
y Ex: when we are cold-> our bodies attempt to make heat by making our muscles work:
shivering
y Longer exposure to cold= increase interior bodily temperature
Influence of the Cultural Environment
y Humans can dramatically affect their environments
y Cold= living in house, harnessing energy to create heat, wearing clothing etc
Biological Diversity in Human Populations
y Adaption: basic biocultural flexibility of humans responding to their environment
Body Build and Facial Construction
y Body build of many birds and mammals may vary according the temperature of the
environment in which they live
y 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
y 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
y 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
y 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
y 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
y Facial structure may also be affected by the environment
y Risenfield: Facial width of rats increased in cold temperatures and their nasal openings grew
www.notesolution.com
Unlock document

This preview shows page 1 of the document.
Unlock all 4 pages and 3 million more documents.

Already have an account? Log in

Document Summary

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. O natural selection may favour certain genes because of certain physical environmental conditions, as in the case of the moths in england (dark/light moths- industrialization-> newly darkened trees; predators could not see dark moths= soon outnumbered light moths) O physical environment can sometimes produce variation even in the absence of genetic change.