Chapter 27 Evolution of Life

Transcription

1 Chapter 27 Evolution of Life 27.1 Origin of Life Age of Planet Earth billion years Oldest Fossils billion years Possible Formation of the First Cells Inorganic molecules reacted to form organic molecules Organic molecules polymerized to become macromolecules Plasma membrane formed Protocells formed 1 Biological Evolution Chemical Evolution photosynthesis and / or cellular respiration macromolecules true cell protocell aggregation polymerization DNA origin of RNA genetic code plasma membrane small organic molecules energy capture abiotic synthesis inorganic chemicals Evolution of Small Organic Molecules Early life may have arose near the surface of the ocean Miller and Urey Experiment (1953) Formation of small organic molecules 27.1 Origin of Life stopcock for adding gases stopcock for withdrawing liquid boiler heat electric spark CH 4 NH 3 H 2 H 2O condenser gases electrode hot water out cool water in liquid droplets small organic molecules cooling early Earth

2 27.1 Origin of Life 27.1 Origin of Life Evolution of Small Organic Molecules Some scientists hypothesize life began in hydrothermal vents deep in the ocean hydrothermal vent Macromolecules RNA-first Hypothesis Ribozymes are RNA molecules that can function as both a genetic substrate and an enzyme If RNA evolved first it could function as both genes and enzymes RNA world Ralph White/Corbis 27.1 Origin of Life The Protocell In lipid environment, phospholipids are known to automatically form liposomes - may be the way plasma membranes first formed The True Cell RNA-first hypothesis - first true cell would have had RNA genes Some viruses have RNA genes Reverse transcriptase produces DNA from RNA Suggests a mechanism as to how cells evolved to have DNA genes

3 27.2 Evidence of Evolution Once a true cell formed, biological evolution began Evolution is the changes that have occurred in living organisms since the beginning of life due to differential reproductive success Some individuals reproduce more than others because they are better suited to their environment Descent with modification All living things share the same fundamental characteristics 27.2 Evidence of Evolution Fossil Evidence Hard body parts are preserved in most cases Often embedded in sedimentary rock Deposited in layers called strata Older than the one above and younger than the one below Transitional fossils Especially significant - represent evolutionary links Transitional Fossils 27.2 Evidence of Evolution wing head wing tail with vertebrae tail feet a. b. a: Jean-Claude Carton/Bruce Coleman, Inc.; b: Joe Tucciarone feathers claws teeth Geological Timescale History of Earth is divided into eras, then periods, and then epochs Based on dating of fossil evidence Relative Dating Method Determines the relative order of fossils and strata but not the actual date Absolute Method Radioactive dating techniques are used to assign an actual date to a fossil Technique is based on the half-life of radioactive isotopes

4 27.2 Evidence of Evolution Pangaea Laurasia Gondwana Laurasia Gondwana Biogeographical Evidence Study of the distribution of species throughout the world Consistent with the hypothesis that when forms are related, they evolved in one locale and the spread The Earth has six biogeographical regions Each has its own distinctive mix of species Barriers prevented evolving species from migrating to other regions Permian period ~250 million years ago Triassic period ~220 million years ago North America South America Africa Eurasia Antarctica Cretaceous period 65 million years ago India Australia Jurassic period 144 million years ago North America South America Africa Antarctica Present day Eurasia India Australia Continental Drift The positions of continents and oceans has shifted through time The distribution of fossils and existing species allows us to determine approximate timeline

5 27.2 Evidence of Evolution Mass Extinctions Large numbers of species become extinct in a short period of time Remaining species may spread out and fill habitats left vacant Five Major Extinctions have occurred Earth may currently be experiencing a sixth mass extinction due to human activities Chase Studio/Photo Researchers, Inc. Cretaceous extinction Due to a meteorite falling to Earth Produced cloud of dust that blocked the sun Evidence of huge crater in Yucatán Peninsula 27.2 Evidence of Evolution 27.2 Evidence of Evolution Anatomical Evidence Common descent offers explanation for anatomical similarities Homologous Structures Same function and same basic structure, indicating a common ancestor Ex: human arm and whale forelimb Analogous Structures Same basic function but different origins Ex: wing of bird and wing of an insect Anatomical Evidence Vestigial Structures Anatomical structures fully functional in one group and reduced, nonfunctional in another Ex: snakes have no use for hindlimbs, and yet some have remnants of hindlimbs in a pelvic girdle and legs

6 bird bat humerus ulna radius metacarpals phalanges Homologous Structures Homology Extends to Embryological Development fish salamander tortoise whale cat horse human chicken pharyngeal pouches human postanal tail 27.2 Evidence of Evolution J.G.M. Thewissen, Parade of fossils link modern whales and dolphins to land ancestors Presence of vestigial pelvic girdle and legs in modern whales is also significant evidence Biochemical Evidence All organisms use same basic biochemical molecules DNA ATP Identical or nearly identical enzymes Many developmental genes are shared Degree of similarity between DNA base sequences and amino acid sequences indicates the degree of relatedness

7 Significance of Biochemical Differences Number of Amino Acid Differences Compared to Human Cytochrome C yeast moth fish turtle duck pig monkey human Cytochrome c is a small protein that plays an important role in the electron transport chain within mitochondria of all cells. Evolution Occurs at the Population Level Genetic changes occur within a population Microevolution Change in gene frequencies within a population over time Population Genetics Population - all members of a species occupying a particular area at the same time Gene pool - the sum total of all alleles of all genes in a population F 1 generation Genotypes: Genotype frequencies: DD 0.04 Dd dd Allele and gamete frequencies: D = 0.20 d = 0.80 Population Genetics Hardy and Weinberg used the binomial equation p 2 + 2pq + q 2 to calculate the genotype and allele frequencies in a population p 2 = DD genotype 2pq = Dd genotype q 2 = dd genotype F 2 generation Sperm Eggs 0.20 D 0.80 d 0.04 DD 0.16 Dd 0.16 Dd Offspring Genotype frequencies: 0.04 DD Dd dd = 1 p 2 + 2pq + q 2 = D 0.80 d 0.64 dd p 2 = frequency of DD genotype (dark-colored) = (0.20) 2 = pq = frequency of Dd genotype (dark-colored) = 2(0.20)(0.80) = 0.32 q 2 = frequency of d d genotype (light-colored) = (0.80) 2 =

8 The data from the previous graphic shows that the next generation will have exactly the same ratio of genotypes as before: The Hardy-Weinberg Principle Allele frequencies in a gene pool will remain at equilibrium, thus constant, in each generation of a large sexually reproducing population as long as the following five conditions are met 1. No mutations 2. No genetic drift 3. No gene flow 4. Random mating 5. No selection The Hardy-Weinberg Principle In real life these conditions are rarely met Significance of the Hardy-Weinberg principle is that microevolution can be detected by noting deviations from a Hardy-Weinberg equilibrium of allele frequencies in the gene pool of a population Early observation Later observation 36% dark-colored phenotype 64% dark-colored phenotype (both): Michael Wilmer Forbes Tweedie/Photo Researchers, Inc.;

9 Genetic Drift Five Agents of Evolutionary Change Mutations Permanent genetic changes Random most often result in no change or a negative effect Genetic Drift Change in allele frequencies due to chance Two main mechanisms Founder Effect Bottleneck Effect 10% of population 20% of population natural disaster kills five green frogs Founder Effect Founder Effect: a few individuals found a colony and their collective genes represent only a fraction of the original gene pool Five Agents of Evolutionary Change Gene Flow Movement of alleles between populations Keeps the gene pools of two or more populations similar Nonrandom Mating Occurs when individuals pair up according to phenotype or genotype Inbreeding is an example Increases frequency of recessive abnormalities in humans Natural Selection

10 Natural Selection Process by which populations adapt to their environment Charles Darwin explained evolution through natural selection Natural Selection Evolution by natural selection requires the following: 1. Individual variation 2. Inheritance 3. Overproduction 4. Differential reproductive success Natural Selection Fitness: measured by the number of fertile offspring produced by an individual Variations that can contribute to fitness can arise from: Mutation Crossing over Independent assortment Most traits on which natural selection acts are controlled by polygenic inheritance Range of phenotypes which follows a bell-shaped curve Natural Selection Three Main Types of Natural Selection Stabilizing Selection Directional Selection Disruptive Selection

11 Stabilizing Selection Stabilizing Selection Extreme phenotypes are selected against Average phenotype is favored Improves adaptation of population to a stable environment Initial Distribution After Time Survival of Young Survival of Young Clutch Size Clutch Size less than 4 eggs 4 to 5 eggs more than 5 eggs After More Time Survival of Young Clutch Size Directional Selection Directional Selection One extreme phenotype is favored Distribution curve shifts in that direction Can occur when population is adjusting to a changing environment Number of Individuals Initial Distribution Body Size Number of Individuals After Time Body Size Number of Individuals After More Time Body Size a. Hyracotherium Merychippus b. Equus

12 Disruptive Selection Two or more extreme phenotypes are selected Two different habitats could result in two different phenotypes in the population Initial Distribution After Time Number of Individuals Number of Individuals Banding Pattern Disruptive Selection Banding Pattern After More Time Number of Individuals Banding Pattern a. b. Bob Evans/Peter Arnold; Maintenance of variation is beneficial because populations with limited variation may not be able to adapt to new conditions should the environment change and may become extinct Forces that promote variation: Mutation generates new alleles Recombination and independent assortment Gene flow Natural selection may favor certain phenotypes but others still remain Diploidy and the heterozygote Heterozygote is the potential protector of recessive alleles Balanced polymorphism Connect between sickle cell disease and malaria

13 27.4 Speciation Species Can be described as a group of subpopulations that are capable of interbreeding and are isolated reproductively from other species Subpopulations of the same species can exchange genes, but different species do not exchange genes Reproductive isolating mechanisms 27.4 Speciation The Process of Speciation Occurs when one species give rise to two species Occurs when reproductive isolation develops Allopatric Speciation: geographical barriers separate a population into two groups Sympatric Speciation: occurs without geographical barriers Ex: Plants - multiplication of chromosome number in one plant may prevent it from successfully reproducing with others of its kind. Self-reproduction can maintain a new species Allopatric Speciation 1. Members of a northern ancestral population migrated southward. COASTAL RANGE MOUNTAINS SIERRA NE VADA MOUNTAINS Ensatina eschscholtzii xanthoptica Ensatina eschscholtzii picta CENTRAL VALLEY Ensatina eschscholtzii eschscholtzii Ensatina eschscholtzii oregonensis 2. Subspecies are separated by California s Central Valley. Some interbreeding between populations does occur. Ensatina eschscholtzii platensis Ensatina eschscholtzii croceater 3. Evolution has occurred, and in the south two subspecies look quite different from one another. Ensatina eschscholtzii klauberi

14 27.4 Speciation The Galapagos Finches Adaptive Radiation Proliferation of a species by adaptation to different ways of life Galápagos Islands finches studied by Darwin Mainland finches migrated to one of the islands Reproduced and eventually spread to all the islands Subjected to different environmental selection pressures Gave rise to many species of finches which differ primarily in beak shape Adapted to allow use of different food sources Medium ground finch, Geospiza fortis Cactus finch, Geospiza scandens Large tree finch, Camarhyncus psittacula Vegetarian finch, Platyspiza crassirostris Small tree finch, Medium tree finch, Small ground finch, Camarhynchus parvulus Camarhynchus pauper Geospiza fuliginosa Sharp-beaked ground finch, Geospiza difficilis Mangrove finch, Large cactus finch, Cactospiza heliobates Geospiza conirostris Woodpecker finch, Cactospiza pallida Warbler finch, Large ground finch, (holding a cactus spine) Certhidea olivacea Geospiza magnirostris (med ground, Mangrove, vegetarian finches): Greg Lasley Nature Photography; (small tree and large cactus finches): Rob and Ann Simpson/Visuals Unlimited; (medium tree finch): David Hosking/Alamy; (small ground and sharp-beaked ground finches): Gerald & Buff Corsi/Visuals Unlimited; (cactus finch): Fritz Polking/Visuals Unlimited; (large tree finch): Steve Bird, Birdseekers Ltd.; (woodpecker finch): R. Koster/OSF/Animals Animals; (warbler finch): Joe McDonald/Animals Animals; (large ground finch): Adrienne Gibson/Animals Animals Speciation Phyletic Gradualism Compared to Punctuated Equilibrium The Pace of Speciation Phyletic Gradualism Change is slow but steady before and after a divergence Explains why so few transitional fossils are found Reproductive isolation cannot be detected in fossils Punctuated Equilibrium Long periods of stasis followed by rapid speciation Occurs relatively rapidly Also can explain lack of transitional fossils Rapid development of changes does not result in recognizable transitional links a. ancestral species new species 1 ancestral transitional link species new species 2 Time b. Time new species 1 ancestral species new species 2

15 27.5 Systematics 27.5 Systematics Reconstructs a phylogeny Evolutionary history of a group of organisms Classification is a part of systematics Ideally organisms are classified according to our present understanding of their evolutionary relationships Linnean classification Taxonomy Identifying, naming, and classifying organisms Taxon Group of organisms as a particular level in a classification system Binomial system Genus and specific epithet Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species 27.5 Classification Phylogenetics - places species into clades Clade - portion of a cladogram Contains a most recent common ancestor and all descendant species All organisms in a clade exhibit the same characteristic May represent single traits on diagram but many traits are used Use homologous structures or DNA sequences Convergent evolution results in analogous structures jaws lamprey shark salamander lizard tiger gorilla human lungs Cladogram amniotic membrane hair loss of tail bipedal

16 27.5 Classification Millions of Years Ago (MYA) Galago Capuchin Green monkey Rhesus monkey Gibbon Chimpanzee Human Modern phylogenetic studies are based on the assumption that the more closely species are related, the fewer changes will be found in molecular nucleotide sequences Three Domain Classification System Five kingdom system based on: Type of cell Level of organization Type of nutrition rrna data supports a three domain system Domain Archaea Domain Bacteria Domain Eukarya plants fungi EUKARYA animals protists protists cyanobacteria heterotrophic bacteria BACTERIA ARCHAEA common ancestor