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4 1 Evolution Anthropology: The Exploration of Human Diversity 11th Edition Conrad Phillip Kottak McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 2 Evolution • • • • • Evolution Genetics Mendel’s Experiments Biochemical, or Molecular, Genetics Population Genetics and Mechanisms of Genetic Evolution • Natural Selection McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 3 Evolution • • • • • • McGraw-Hill Polymorphisms Understanding Ourselves Mutations and Variety Random Genetic Drift Gene Flow The Modern Synthesis © 2005 The McGraw-Hill Companies, Inc. 4 Evolution • Humans have uniquely varied ways— cultural and biological—of evolving, of adapting to environmental stresses • Many scholars became interested in biological diversity and our position within the classification of plants and animals during 18th century McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 5 Evolution • Creationism—biological similarities and differences originated at the Creation • Linnaeus (1707-1778) developed first comprehensive and still influential classification, or taxonomy, of plants and animals Fossil discoveries during the 18th and 19th centuries raised doubts about creationism McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 6 Evolution • Catastrophism—modified version of Creationism accounts for the fossil record by positing divinely authored worldwide disasters that wiped out creatures represented in the fossil record The alternative to creationism and catastrophism was transformism, also called evolution McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 7 Evolution • Darwin influenced Lyell’s Principle of Uniformitarianism—explanations for past events should be sought in the long-term action of ordinary forces that still work today • Natural Selection—process by which nature selects the forms most suited to survive and reproduce in a given environment McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 8 Evolution • For natural selection to work on a given population, there must be: – Variety within that population – Competition for strategic resources Process of natural selection continues as long as the relationship between the population and its environment remains the same McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 9 Genetics • Genetic science emerged after Darwin – Mendelian Genetics—studies ways in which chromosomes transmit genes across generations – Population Genetics—investigates natural selection and other causes of genetic variation, stability, and change in breeding populations McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 10 Mendel’s Experiments • Austrian monk Gregor Mendel began a series of experiments that revealed basic principle of genetics in 1856 – Studied inheritance of seven contrasting traits in pea plants – Discovered heredity is determined by discrete particles or units McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 11 Mendel’s Experiments – Concluded that although a dominant form could mask the other form in hybrid, or mixed, individuals, the dominated trait—the recessive—was not destroyed – Basic genetic units Mendel described were factors (now called genes or alleles) located on chromosomes McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 12 Mendel’s Experiments – Alleles—biochemically different forms of a given gene • Heterozygous—dissimilar alleles of a gene in an offspring • Homozygous—two identical alleles of a gene in an offspring • Dominance produces a distinction between genotype—hereditary makeup and phenotype—expressed physical characteristics McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 13 Mendel’s Experiments • Independent Assortment and Recombination – Independent Assortment—Mendel’s discovery that traits are inherited independently of one another – Recombination—combination of genetic traits in an offspring; creates new types on which natural selection can operate McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 14 Mendel’s Experiments • Mendel’s Second Set of Experiments with Pea Plants – Insert Figure 4.1 McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 15 Mendel’s Experiments • Simplified Representation of a Normal Chromosome Pair – Insert Figure 4.2 McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 16 Mendel’s Experiments • Punnett Squares of a Homozygous Cross and a Heterozygous Cross – Insert Figure 4.3 McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 17 Mendel’s Experiments • Determinants of Phenotypes (Blood Groups) in the ABO System – Insert Figure 4.4 McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 18 Biochemical, or Molecular, Genetics • Studies structure, function, and changes in genetic material – Mutations—changes in the DNA molecules of which genes and chromosomes are built – Gametes—sex cells that make new generations McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 19 Biochemical, or Molecular, Genetics • DNA molecule is a double helix – RNA carries DNA’s message to its cytoplasm (outer area) – Structure of RNA, with paired bases, matches DNA DNA, with RNA’s assistance, initiates and guides the construction of hundreds of proteins necessary for bodily growth, maintenance, and repair McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 20 Biochemical, or Molecular, Genetics • A Double-Stranded DNA Molecule – Insert Figure 4.5 McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 21 Biochemical, or Molecular, Genetics • Crossing Over – Insert Figure 4.6 McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 22 Biochemical, or Molecular, Genetics • Cell Division – Mitosis—ordinary cell division, wherein one cell splits to form two identical cells McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 23 Biochemical, or Molecular, Genetics • Cell Division – Meiosis—special process by which sex cells are produced • 4 cells produced from • Fertilization allows the one products of meiosis from • Each cell carries half one parent to recombine the genetic material of with those from the the original cell (i.e., other parent twenty-three chromosomes instead • Chromosomes sort independently of forty-six) McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 24 Biochemical, or Molecular, Genetics • Crossing Over – Process where homologous chromosomes exchange segments by breakage and recombination Independent assortment of chromosomes permits parents’ genotypes to be assorted in more than 8 million different ways McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 25 Population Genetics and Mechanisms of Genetic Evolution • Population genetics studies stable and changing populations in which most breeding normally takes place – Gene Pool—refers to alleles and genotypes within breeding population McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 26 Population Genetics and Mechanisms of Genetic Evolution – Genetic Evolution—change in the frequency of alleles in breeding population from generation to generation • Any factor that contributes to a change considered mechanism of genetic evolution Natural selection Genetic drift McGraw-Hill Mutation Gene flow © 2005 The McGraw-Hill Companies, Inc. 27 Natural Selection • Genotype refers to the genetic makeup of an organism • Phenotype is the organism’s evident biological characteristics – Natural selection only act on phenotypes – Environmental influence in this interaction extremely important – Lends great plasticity to human biology McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 28 Natural Selection • Directional Selection – After several generations of selection, gene frequencies change • Natural selection will have occurred • Adaptive—favored by natural selection McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 29 Natural Selection • Directional Selection – Directional selection—long-term selection of the same trait(s) • Directional selection continues as long as environmental forces stay the same – Sexual selection—certain traits of one sex selected because of advantages they confer in winning mates McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 30 Polymorphisms • Balanced polymorphism—frequencies of two or more alleles of a gene remain constant from generation to generation Sickle-Cell Anemia • HbA and HbS alleles largely determines hemoglobin production in humans • Homozygous HbA produces normal hemoglobin • Homozygous HbS produces lethal sickle-cell anemia • Heterozygosity for this gene produces (in some circumstances) deleterious but nonlethal sickle-cell syndrome McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 31 Polymorphisms – HbS existed at surprisingly high frequencies in certain populations in Africa, India, and the Mediterranean • Heterozygous form produced phenotype resistant to malaria – Demonstrates relativity of evolution through national selection McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 32 Polymorphisms • Distribution of Sickle-Cell Allele and Falciparum Malaria in the Old World – Insert Figure 4.7 McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 33 Understanding Ourselves • Human biology is plastic, but only to a degree • Plasticity through culture steps in to complement human biological plasticity McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 34 Mutations and Variety • Mutation major source of genetically transmitted variety • Variants produced through mutation can be especially significant if there is change in selective forces McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 35 Random Genetic Drift • Random genetic drift—loss of alleles from a population’s gene pool through chance Lost alleles reappear in gene pool only through mutation McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 36 Gene Flow • Exchange of genetic material between populations of the same species Alleles spread through gene flow even when selection not operating on the allele McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 37 Gene Flow • Important in study of origin of species – Species—group of related organisms whose members can interbreed to produce offspring that live and reproduce – Gene flow tends to prevent speciation— formation of new species McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 38 Gene Flow • Gene Flow between Local Population – Insert Figure 4.8 McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 39 The Modern Synthesis • Currently accepted view of evolution – Microevolution—small-scale changes in allele frequencies over just a few generations – Macroevolution—large-scale changes in allele frequencies in a population over a longer time period Microevolution and macroevolution happen in the same way and for the same reasons McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 40 The Modern Synthesis • Gradual or Rapid Change – Darwin: minor alterations in gene pool, accumulating generation after generation, added up to major changes McGraw-Hill © 2005 The McGraw-Hill Companies, Inc. 41 The Modern Synthesis • Gradual or Rapid Change – Punctuated equilibrium—long periods of stasis, during which species change little, interrupted by evolutionary leaps Sudden environmental change, rather than Species radical environmental extinctioncan andsurvive replacement, presents shifts, but more common fate isto extinction possibility for pace of evolution speed up McGraw-Hill © 2005 The McGraw-Hill Companies, Inc.