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Transcript
Evolution (Chapters 17-20) I. History of the Development of the Theory of Evolution A. Definitions 1. evolution = change in the genetic makeup or gene frequency of a population over time 2. evolution = origin of “new” organisms by descent and modification from previously existing forms or species B. Macroevolution vs microevolution 1. microevolution – small changes within a species 2. macroevolution – large changes when one species gives rise to a different species or higher taxonomic group 3. taxonomic levels: C. Lamarck (1809) – Inheritance of acquired characteristics (Giraffe – not correct) D. Charles Darwin (1859) – Origin of Species by means of Natural Selection – developed the theory of evolution proposing that species changed slowly (gradualism) through time via natural selection 1. natural selection = differential reproduction of genotypes: individuals with some genotypes produce more offspring than those of others and if successful in reproducing, these characteristics become more common; nature favors those characteristics that help a species survive and reproduce successfully (survival and reproduction of the “best adapted”) a. organisms have genetic variations b. organisms struggle to exist c. organisms differ in “fitness” 2. Darwin’s voyage on the Beagle – observations of organisms on Galapagos Islands (finches, tortoises, etc.), influences of Malthus (struggles for existence and competition) and Hutton (slow, geological changes – uniformitarianism) 3. Alfred Wallace also proposed the mechanism of “natural selection” E. Evidence for the Theory of Evolution by Natural Selection 1. artificial selection – animal and plant breeding 2. fossils – remains of prehistoric life a. organisms have changed through time b. geologic column – simpler organisms are found in deeper strata, more complex organisms are found in higher strata; disappear of species and types of organisms with appearance of new forms; transitional forms; data of strata and fossils via half-life; changes in relative abundance of types of organisms c. construction of fossil genealogies and evolutionary “trees” 3. comparative anatomy a. similar organisms have similar structures, but these structures may be used for a different function (homologous): bat’s wing, whale’s flipper, cat’s foreleg, horse’s front leg, human arm). All of these originate from the same structure during embryonic development and have the same bones, but each limb has a different function and the bones are modified to fit that use) – reflect adaptive radiation or divergent evolution; organisms have these structures because they have a “common ancestor”) b. vestigial organs and structures – seem to have lost their original purpose or function (appendix, hind limb bones in some marine mammals such as whales and some snakes) c. analogous structures – have similar functions but may be different in their structures and embryonic development (bird’s wing, insect wing) – may reflect – may reflect convergent evolution 4. Comparative embryology a. embryo contains structures not found in the adult (pharyngeal slits and a “tail” in vertebrate embryos), implies a “common ancestor” b. new features may have developed from “remodeling” of earlier features (primitive vs advanced) c. early development: protostomes (Mollusca, Arthropoda) vs deuterostomes (Chordata and Echinodermata); coelomate vs acoelomate vs pseudocoelomate animals 5. comparative biochemistry a. order of nitrogen bases in similar segments of DNA b. order of amino acids in proteins 6. biogeography – where plants and animals live and why a. puzzles: Why did the Galapagos islands have more species of finches than the mainland of S America and how were these groups related? Why were marsupials confined mostly to Austrailia? b. From ancestral groups, new populations could spread , become isolated, and through natural selection become new species (adaptive radiation) c. Islands have many endemic species (unique to that location); mainland species may have migrated to islands, become isolated, adapted to different conditions, and eventually become new species (Darwin’s finches and tortoises) II. Relationships between evolution and natural selection A. Natural selection is the driving mechanism for evolutionary change B. Basic concepts linking evolution and natural selection 1. individuals of a species vary 2. some variations are genetic (mutations, crossing over, random assortment, etc.) 3. more individuals are produced through reproduction than survive 4. individuals with some traits are more likely to survive than others 5. those that are more successful in surviving and reproducing will have more offspring with those particular traits 6. nature provides “selective pressure” favoring certain genotypes and phenotypes 7. thus, organisms change through time 8. as these changes “accumulate” new species may form or “evolve” C. Examples of Natural Selection in action 1. peppered moths in England 2. resistance of plants to toxic metals 3. resistance of insects to pesticides 4. resistance of bacteria to antibiotics 5. genetic variations in human races or ethnic groups III. Population genetics and evolution (Chapter 18) A. Population - basic unit of study in evolutionary change 1. population = all the members of a species occupying a particular area at the same time and freely interbreeding (part of the same “gene pool”) 2. in the absence of natural selection or certain other influences, the gene frequencies within the gene pool remain constant 3. different populations may become isolated from each other. 4. under environmental influences (natural selection), gene frequencies may change, leading to evolution and formation of new species B. Hardy Weinberg Law and Equations provide a model for examining evolutionary change within a population 1. Law = In a large population of diploid organisms, the gene frequencies will remain constant and no evolution will occur if 5 conditions are met: a. no mutation b. no mating preferences c. large population size d. no gene flow – immigration or emigration e. no selection 2. sexual reproduction by itself can not produce evolutionary change, although it does “shuffle” genes, producing genetic variation 3. evolution can be defined as: a change in gene frequencies in a population through time 4. if one or more of the above conditions are not met, gene frequencies may change and hence evolution can occur 5. using the HardyWeinberg equations to determine gene frequencies and genotype frequencies p2 + 2pq + q2 = 1 AA Aa aa (genotypes and phenotypes) p + q =1 A a (gene or allele frequencies) these only work for a simple, Mendelian trait example: C. Causes of evolutionary change 1. mutations – introduce new genes and hence genetic variation which can be selected for or against by nature (most mutations are harmful) 2. mating preferences (selective breeding and artifical selection) 3. genetic drift – change in the gene pool and hence gene frequencies that occurs when a small group of individuals forms a separate population (i.e. founder effect) 4. gene flow between populations neighboring populations may contribute genes to another population a. the closer the populations, the greater the changes of gene flow b. cline = character or trait that shows a gradient of variation across an area c. gene flow between populations makes them more similar, the greater the distance between populations, the less the chance of gene flow and the greater the genetic differences 5. natural selection – nonrandom, differential survival and reproduction of genotypes from one generation to the next, does not always “act” in the same manner on a trait a. stabilizing selection – average phenotypes have a selective advantage over extremes in either direction b. directional selection – phenotypes of one extreme are favored or have an advantage c. disruptive selection – extremes of a range of phenotypes are favored relative to intermediate forms, may lead to two distinct characteristics and eventually speciation D. What promotes and maintains genetic variability in populations 1. heterozygote advantage a. sickle cell anemia b. hybrid offspring may have superior traits over their parents 2. genetic polymorphism – the continued occurrence in the same place at the same time of two or more genetic variants of the same trait or set of traits a. sexual differences between males and females (sexual dimorphism), human ABO blood type, etc. 3. rapid population growth 4. decrease in selective pressures (few predators, reduced competition, favorable environments and habitats, etc.) E. What is a species? 1. species – one or more populations of organisms capable of interbreeding with each other in nature 2. different species live in reproductive isolation from each other 3. reproductive isolating mechanisms include: a. prezygotic: habitat isolation, temporal isolation, behavioral isolation, mechanical isolation b. postzygotic: gamete isolation, zygote mortality, offspring sterility 4. all the members of the same species share the same gene pool. 5. species identification and differentiation is often based upon morphological differences. Type specimens representing species are preserved and compared. 6. tests for evaluating a “species” a. reproductive isolation b. behavioral differences c. differences in protein structure (order of amino acids) d. differences in DNA (order of nitrogen bases) F. Speciation – How are new species formed? 1. allopatric speciation – population becomes physically separated from the rest of the species and becomes so different that members can no longer interbreed with the original group, and therefore become a “new species” a. islands – Hawaiian honeycreepers, Darwin’s finches b. Pleistocene glaciations – warblers c. Squirrel species on opposite sides of the Grand Canyon d. Often leads to adaptive radiation and/or divergent evolution 2. sympatric speciation – formation of a new species within a population (usually involves a drastic change in the chromosome number so individuals can no longer freely interbreed) a. polyploidy – irregularities in meiosis (common in plants) 3. How quickly do new species and/or groups of organisms form? a. Darwinian view – slow, gradual (Gradualism) b. Alternative view – Punctuated Equilibrium – evolutionary change is variable – sometimes fast, sometimes slow: evolutionary breakthroughs or traits that offer significant advantages often occur in small populations, these then spread quickly and may have little chance for fossilization since they may only exist for short periods of geological time (postulated to possibly explain gaps in the fossil record or lack of certain transitional forms) IV. Origin of Life and Patterns in Evolution (Chapter 19) A. Origin of Life??? 1. necessary conditions on pre-biotic earth a. long periods of time b. absence or low concentrations of molecular oxygen (O2), oxygen decomposes organic molecules as they form under most natural conditions (reducing atmosphere rather than an oxidizing atmosphere) c. molecules present: H2, H2O, CH4, NH3, CO2, CO, etc. 2. biochemical evolution and chemical selection a. formation of simple, organic chemicals (amino acids) from inorganic chemicals with the addition of appropriate energy sources (heat, radiation, radioactivity, lightning, etc.) and under a reducing atmosphere (Oparin’s hypothesis and Miller’s experiment) b. monomers polymers: dehydration synthesis of monomers to make polymers (protenoids) with ironnickel sulfides and clay particles acting as inorganic catalysts c. formation of aggregates – spheres with membrane like poperties (phospholipids) and organic molecules inside (proteins, etc); reactions begin to occur inside d. “chemical selection” favors activity and longevity (chemical reactions with catalysts) e. energy metabolism may have relied upon molecules such as ATP, GTP, CTP, UTP, etc “protocell” f. anaerobic fermentation may have been the first “metabolic” pathway g. heterotrophs autotrophs h. anaerobic fermentation and chemosynthesis photosynthesis O2 aerobic respiration i. origin of DNA (chemical code of life)??? Proteins RNA DNA (reverse transcription, RNA genes) 3. prokaryotes (heterotrophs first, then autotrophs), bacteria then blue green bacteria 4. prokaryotes eukaryotes (endosymbiont theory) B. History of Life on Earth (fossil records) 1. earth = 4.5-5 billion years old 2. first primitive life forms (2.8-3.5 billion years ago) 3. eukaryotes (1.8 billion years ago) 4. Eras – Cenozoic, Mesozoic, Paleozoic, and Archeozoic are divided into Periods (Cretaceous, Jurassic, Triassic, etc. are divided into Epochs (Holocene, Pleistocene, Pliocene, Miocene, etc.) 5. Cambrian Period during the Paleozoic 570 million years ago, a huge explosion and diversity of fossil types appeared with major animal groups (Arthropoda, Mollusca, Echinodermata) a. before that time, only very few simple fossils existed 6. Evolution of kingdoms and phyla Plantae a. Monera Protista Fungi Animalia Protista invertebrates (animals with a backbone) vertebrates b. Protista Protostomes (Arthropoda, Mollusca, Annelida) Deuterostomes (Echinodermata, Chordata) d. vertebrates: fish amphibians reptiles birds mammals c. plants: protista chlorophyta (green algae) simple land plants that reproduce with spores (Lycophyta, Bryophyta - mosses) land plants with spores, leaves, roots, and stems (Pterophyta – ferns) higher plants that reproduce with seeds (Gingophyta), cones and seeds (Coniferophyta – conifers, i.e. redwoods, pines, cedars, junipers) and flowers and seeds (Anthophyta – oak, tulip, rose, grass, etc.) V. Taxonomy = Classification of Living Organisms (Chapter 20) A. Binomial nomenclature = all living organisms are assigned a two part name consisting of the genus and species written in latin 1. dog = Canis familiaris 2. wolf = Canis lupus 3. human = Homo sapiens B. Organisms are placed into taxa (groups) based upon cell structure, complexity, morphology, structures, and possible evolutionary relationships C. Eight levels of classification 1. eight categories hierarchy 2. domains 3. kingdoms D. Taxonomy (classification) and evolutionary relationships 1. evolutionary systematics – classification should reflect both geneology (common ancestry) and genetic relationships (shared genetic traits and characteristics) 2. cladistics – taxa (groups) should be monophyletic containing a common ancestor and its descendants; polyphyletic taxa with several ancestors should be broken up. a. clade = common ancestor and all the groups descended from it using a specific characteristic b. monophyletic – one evolutionary “line” c. polyphyletic – made up of several evolutionary “lines” d. compares ancestral (conservative) versus derived or later characteristics e. utilizes cladograms to show relationships E. Molecular systematics 1. compares order of amino acids in specific proteins (cytochrome C in the electron transport chain) 2. compares order of nitrogen bases in specific RNA (rRNA) and DNA molecules (mtDNA) 3. molecular clocks can be developed that utilize changes in molecular structure and/or mutation rates to postulate evolutionary rates of change (5.1% change in nucleic acid difference to 2.5 million years) Human Evolution – Chapter 21 I. Classification of Humans A. Kingdom B. Phylum C. Class D. Order E. Family F. Genus G. Species II. Primates A. Major characteristics 1. Mobile forelimbs and hind limbs 2. binocular vision with flattened face 3. reduced reproductive rate – single birth 4. opposable thumb and in some cases – big toes, grasping “hands” 5. expanded, complex brain with emphasis on learned behavior B. Prosimians vs anthropoids 1. prosimians – lemurs and tarsiers 2. anthropoids – New World monkeys, Old world monkeys, hominoids – apes and humans a. Proconsul – ancestral hominid (size of baboon, brain = 165 cc) b. Hominids = skeletal features – spine, pelvis, and limb bones; jaw shape, brain size differ from apes c. Humans are most similar in DNA and other skeletal features to apes III. Evolution of Hominids A. Australopithecines – evolved and diversified in Africa (gracile vs robust) 1. Australopithecus afarensis (Lucy) – walked upright, small brain (400 cc), sexual dimorphism (males vs females were distinct) 2. gracile forms (slight of frame) are believed to be more primitive to robust forms (massive jaws, stronger upper body) 3. Australopithecus africanus and A. robustus (brain = 500cc) B. Evolution of Humans 1. Genus Homo: main features – brain size is 600cc or greater, jaw similar to humans, face is smaller and more flat than humans, tool manufacture and use seems evident 2. Homo habilis (brain = 775 cc) 3. Homo ergaster and H. erectus (brain = 900cc) 4. Homo sapiens (modern humans) a. appeared 300,000 years ago b. multiregional continuity vs out of Africa hypothesis c. Homo neanderthalensis - archaic modern human, 50,000 years ago) d. Cromagnon (Homo sapiens) – brain size (1300cc), 100,000 years ago