Anthropology Appreciating Human Diversity Fifteenth Edition Conrad Phillip

Anthropology Appreciating Human Diversity Fifteenth Edition Conrad Phillip Kottak University of Michigan Mc. Graw-Hill © 2013 Mc. Graw-Hill Companies. All Rights Reserved.

C H A P T E R EVOLUTION AND GENETICS 5 -2

EVOLUTION AND GENETICS • • Evolution Genetics Biochemical, or Molecular, Genetics Population Genetics and Mechanisms of Genetic Evolution • The Modern Synthesis 5 -3

EVOLUTION AND GENETICS • What is evolution, and how does it occur? • How does heredity work, and how is it studied? • What forces contribute to genetic evolution? 5 -4

EVOLUTION • Humans have uniquely varied ways—cultural and biological—of adapting to environmental stresses • Many scholars became interested in biological diversity and our position within the classification of plants and animals during the 18 th century 5 -5

EVOLUTION • Creationism: biological similarities and differences originated at the Creation • Linnaeus (1707– 1778) developed the first comprehensive and still influential classification, or taxonomy, of plants and animals • Fossil discoveries during the 18 th and 19 th centuries raised doubts about creationism 5 -6

EVOLUTION • Catastrophism: modified version of creationism that accounts for the fossil record by positing divinely authored worldwide disasters that wiped out creatures represented in the fossil record • Both theories assert that similarities and differences from creation have not changed 5 -7

THEORY AND FACT • Evolution: transformation of species; descent with modification • Alternative to creationism and catastrophism • Darwin best known of evolutionists 5 -8

THEORY AND FACT • Darwin influenced by: • Theory of evolution – belief that species arise from others through a long and gradual process of transformation; all life forms are related and the number of species has increased over time • Grandfather, Erasmus Darwin, who proclaimed a common ancestry of all animals • Lyell’s principle of uniformitarianism: the present is the key to the past; - past geological events can best be explained by observing ongoing events of the present and generalizing backward through time • Darwin applied uniformitarianism to living things; contributed a theory of evolution through natural selection – how evolution occurred 5 -9

THEORY AND FACT • Darwin proposed natural selection to explain the origin of the species, biological diversity, and similarities among related life forms • Reached the conclusion along with Alfred Wallace • Natural selection: the process by which nature selects the forms most suited to survive and reproduce in a given environment • Variety within that population • Competition for strategic resources • Giraffes – long versus short necks • Argues that organisms that have a better fit within their environment, will reproduce more frequently than those less fit • Reproduction is the key • Natural selection continues today • Peppered moth 5 -10

Theory and Fact 5 -11

GENETICS • Genetic science helps explain causes/origin of biological variation • Mendelian genetics: ways in which chromosomes transmit genes across generations • Biochemical genetics: examines structure, function, and changes in DNA • Population genetics: investigates natural selection and the causes of genetic variation, stability, and change 5 -12

MENDEL’S EXPERIMENTS • Austrian monk Gregor Mendel began series of experiments that revealed basic principle of genetics in 1856 • Studied inheritance of seven contrasting traits in pea plants • Concluded that heredity is determined by discrete particles or units (genes) that may disappear in one generation and reappear in the next 5 -13

MENDEL’S EXPERIMENTS • Observed two traits: dominant and recessive • Dominant forms appear in each generation/recessive forms are masked when paired with dominant form of same trait • Concluded that a dominant form could mask another form in hybrid individuals, without destroying the recessive trait • Basic genetic units Mendel described were factors (now called genes or alleles) located on chromosomes 5 -14

Figure 5. 1: Mendel’s Second Set of Experiments with Pea Plants 5 -15

MENDEL’S EXPERIMENTS • Chromosome: a paired length of DNA, composed of multiple genes • Gene: a place (locus) on a chromosome that determines a particular trait • Allele: a variant to a particular gene 5 -16

Figure 5. 2: Simplified Representation of a Normal Chromosome Pair 5 -17

MENDEL’S EXPERIMENTS • Heterozygous: dissimilar alleles of a gene in an offspring • Homozygous: two identical alleles of a gene in an offspring • Genotype: organism’s hereditary makeup • Phenotype: evident biological traits • Dominance produces a distinction between genotype and phenotype 5 -18

Figure 5. 3: Punnett Squares of a Homozygous Cross and a Heterozygous Cross 5 -19

Figure 5. 4: Determinants of Phenotypes (Blood Groups) in the ABO System 5 -20

INDEPENDENT ASSORTMENT AND RECOMBINATION • Independent assortment: traits are inherited independently of one another • Recombination: traits may appear in new combinations with other traits; new types in an offspring on which natural selection can operate; two main ways produces variety 5 -21

BIOCHEMICAL, OR MOLECULAR, GENETICS • Mutation: changes in the DNA molecules of which genes and chromosomes are built; produces variety (source of new forms on which natural selection may operate) BIOCHEMICAL OR MOLECULAR GENETICS 5 -22

CROSSING OVER • Crossing over: • Chromosomes temporarily intertwine in the course of reduplication and exchange lengths of their DNA • the process wherein homologous chromosomes exchange segments by breakage and recombination • Can occur with any chromosome pair • An important source of variety on which natural selection operates 5 -23

Figure 5. 6: Crossing Over 5 -24

MUTATION • • • Mutations: the most important source of variety upon which natural selection acts Chromosomal rearrangement: pieces of a chromosome break off and reattach someplace else on that chromosome • A mismatch of chromosomes resulting from arrangement can lead to congenital disorders, cancer, and possibly to speciation Chromosomes may also fuse: • When ancestors of humans split off from those of chimpanzees around six milion years ago, two ancestral chromosomes fused together in the humans line • Humans have 23 chromosome pair versus 24 for chimps 5 -25

MUTATION • Approximately three mutations will occur in every sex cell • Most mutations are neutral • Evolution depends on mutations • Mutations are major source of genetically transmitted variety • Mutations may be neutral, harmful, or acquire an adaptive advantage through changing selective forces 5 -26

NATURAL SELECTION • Genotype: the genetic makeup of an organism • Phenotype: organism’s biological traits (outward physical appearance as well as internal organs, tissues, and cells and physiological processes and systems) • Natural selection acts only on phenotypes • Human biology has considerable plasticity • The environment works on a genotype to build a phenotype • Diet and altitude affect how a person grows 5 -27

DIRECTIONAL SELECTION • After several generations of selection, gene frequencies change • Adaptive traits (favored by natural selection) will be selected from generation to generation • Directional selection (long-term selection of same traits) continues as long as environmental sources stay the same • Maladaptive genes removed from gene pool • If environment changes, new selective forces start working, favoring different phenotypes • Selection operates only on traits that are present in a population • Favorable mutation may occur but doesn’t usually happen just because one is needed or desirable; many species are extinct because they couldn’t adapt to environmental shifts • Humans adapt rapidly to environmental variation by modifying biological responses and learned behavior 5 -28

SEXUAL SELECTION • Selection also operates through competition for mates • Sexual selection: based on differential success in mating; a selection of traits that enhances mating success 5 -29

GENE FLOW • Gene flow: exchange of genetic material between populations of the same species • Direct or indirect interbreeding • Allele that isn’t advantageous in one environment might reach an environment in which it has selective advantage • Alleles spread through gene flow even when selection not operating on the allele • Species: group of related organisms whose members can interbreed to produce offspring that live and reproduce • Gene flow tends to prevent speciation: the formation of new species 5 -30

Figure 5. 8: Gene Flow between Local Populations 5 -31

THE MODERN SYNTHESIS • Currently accepted view of evolution: • Modern Synthesis: combination of Darwin’s theory of evolution by natural selection and Mendel’s genetic discoveries • Speciation occurs when related populations become reproductively isolated from one another • Microevolution: small-scale changes in allele frequencies over just a few generations, but without speciation • Macroevolution: large-scale changes in allele frequencies in a population over a longer time period, which result in speciation 5 -32

PUNCTUATED EQUILIBRIUM • Punctuated equilibrium: long periods of stasis (stability) may be interrupted by evolutionary leaps (revealed in fossil record) • Occurs through: • Extinction of one species followed by invasion of closely related species • Replacement of one species by a more fit related group in particular environment • Period of sudden environmental change that permits survival of radically altered species with significant mutations or a combination of genetic changes • Sudden environmental change offers possibility for the pace of evolutions to speed up • Species can survive radical environmental shifts, but extinction is more common • Extinction of dinosaurs was accompanied by rapid spread of mammals and birds 5 -33

Darwin Cartoons 5 -34