Presentation on theme: "Human Variation and Adaptation"— Presentation transcript:
1 Human Variation and Adaptation Chapter 15 & 16Human Variation and Adaptation
2 Chapter Outline Historical Views of Human Variation The Concept of RaceRacism & IntelligenceContemporary Interpretations of Human VariationHuman Biocultural EvolutionPopulation GeneticsThe Adaptive Significance of Human VariationThe Continuing Impact of Infectious Disease
3 Historical Views of Human Variation Early human classificationBiological determinismEugenics - "race improvement““Three generations of imbeciles is enough”The Mismeasure of Manby S.J. Gould
4 Traditional Concept of Race Since the 1600s, race = ethnicity.Biological fallacy but social reality.The characteristics that define races are influenced by several genes, and exhibit a continuous range of expression.More genetic variation within one race than other “different” races.
5 RacismBased on false belief that intellect and cultural factors are inherited with physical characteristics.Uses culturally defined variables to typify all members of particular populations.Assumes that one's own group is superior.A cultural phenomenon found worldwide.
6 IntelligenceGenetic and environmental factors contribute to intelligence.Many psychologists say IQ scores measure life experience.Innate differences in abilities reflect variation within populations, not differences between groups.There is no convincing evidence that populations vary in regard to intelligence.
7 Human Polymorphisms Polymorphisms Genetic trait with 2+ alleles. Used as a tool to understand evolutionary processes.Clinal DistributionsA cline is a gradual change in the frequency of a trait or allele in populations dispersed over geographical space.Example: The distribution of the A and B alleles in the Old World.
8 Distribution of the B Allele in Indigenous Populations
9 Polymorphisms at the DNA Level Molecular biologists have recently uncovered DNA variability in various regions of the genome.Scattered through the human genome are microsatellites, sites where DNA segments are repeated.Each person has a unique arrangement that defines their distinctive “DNA fingerprint.”
10 Evolutionary Interactions Affecting the Frequency of the Sickle-cell Allele
11 Population GeneticsThe study of the frequency of alleles, genotypes, and phenotypes in populations from a microevolutionary perspective.A gene pool is the total complement of genes shared by the reproductive members of a population.Breeding isolates are populations that are isolated geographically and/or socially from other breeding groups.
12 Hardy-Weinberg Equilibrium The mathematical relationship expressing the predicted distribution of alleles in populations; the central theorem of population genetics.Provides a tool to establish whether allele frequencies in a human population are changing (see appendix C, p.391).Formula= p2 + 2pq + q2p= frequency of dominant alleleq= frequency of recessive allele
13 Factors that Act to Change Allele Frequencies New variation (i.e., mutation)Redistributed variation (i.e., gene flow or genetic drift)Selection of “advantageous” allele combinations that promote reproductive success (i.e., natural selection, sexual selection)
14 Adaptive Significance of Human Variation Human variation is the result of adaptations to environmental conditions.Physiological response to the environment operates at two levels:Long-term evolutionary changes characterize all individuals within a population or species.Short-term, temporary physiological response is called acclimatization.
16 Pigmentation and Geographical Divisions Before 1500, skin color in populations followed a geographical distribution, particularly in the Old World.Populations with the greatest amount of pigmentation are found in the tropics.Populations with lighter skin color are associated with more northern latitudes.
17 Skin Color Influenced by three substances: Hemoglobin, when it is carrying oxygen, gives a reddish tinge to the skin.Carotene, a plant pigment which the body synthesizes into vitamin A, provides a yellowish cast.Melanin, has the ability to absorb ultraviolet radiation preventing damage to DNA.
18 Thermal EnvironmentMammals and birds have evolved complex physiological mechanisms to maintain a constant body temperature.Humans are found in a wide variety of thermal environments, ranging from 120° F to -60° F.Human Response to HeatLong-term adaptations to heat evolved in our ancestors:Sweat GlandsVasodilation
19 Human Response to Cold Short-term responses to cold: Metabolic rate and shiveringNarrowing of blood vessels to reduce blood flow from the skin, vasoconstriction.Increases in metabolic rate to release energy in the form of heat.
20 High AltitudeMultiple factors produce stress on the human body at higher altitudes:Hypoxia (reduced available oxygen)Intense solar radiationColdLow humidityWind (which amplifies cold stress)
21 Infectious DiseaseCaused by invading organisms such as bacteria, viruses, or fungi.Throughout evolution, disease has exerted selective pressures on human populations.Disease influences the frequency of certain alleles that affect the immune response.
22 Impact of Infectious Disease Before the 20th century, infectious disease #1 limiting factor.Since the 1940s,antibiotics reduced mortality rates.In the late 1960s,war against infectious disease won.Between 1980 and 1992 deaths from infectious disease increased by 58%.Increases may be due to overuse of antibiotics.