Evolution = “Descent with Modification” 1. Organisms evolved due to being spread over different habitats and therefore adapting and modifying themselves to fit the habitat. 2. Natural Selection • A population of organisms can change over generations if certain inheritable traits leave more offspring than others and those others get the chance to reproduce and continue the lineage. • Evolutionary Adaptation
Evidence of Evolution: Fossil Record Fossils chronologically ordered in rock layers
Evidence of Evolution: BiogeographyGeographic distribution of species: Australian marsupials
HOMOLOGY Evidence of Evolution: Comparative Anatomy and Embryology
Evidence of Evolution: Molecular Biology Notice that a Chimp is more genetically related to a human than to an Old World Monkey!
Adaptive Evolution Natural Selection = EditingThe finches of The Galapagos Islands: The original finch developed into 14different species. What was the cause for the offshoots?
Darwinism Meets Genetics• A population is the smallest unit of evolution. – Natural selection acts on individuals. – However the evolutionary impact of natural selection is only apparent in tracking how a population changes over time.• Population Genetics emphasizes the extensive genetic variation within populations and tracks the genetic make-up of populations over time. – Not all variation in a population is inheritable. – Only the genetic component of variation is relevant to natural selection. – Many variable traits in a population result from the combined effect of several genes. Polymorphism
Microevolution1. Genetic Drift Def: A change in the gene pool of a small population due to chance. The best measure of Darwinian fitness is the number of fertile offspring an individual leaves.
Genetic equilibrium- allele frequenciesremain constant.To maintain at equilibrium…1.Random mating2.Population must be very large3.No immigration or emigration4.No mutations5.No natural selection
Microevolution Cont.2. Gene Flow Def: The genetic exchange with another population.3. Mutations – A change in an organism’s DNA sequence. – Ultimate source of genetic variability.4. Natural Selection – Directional Selection (selecting in favor of an extreme phenotype) – Disruptive (Diversifying) Selection (leads to a balance between two or more contrasting phenotypic forms) – Stabilizing Selection (maintains variation in a narrow range)
•Resistant Genes •Immediate Benefits •Long term Disaster •Evolution direct connection to daily lives
Macroevolution• Def: Major biological changes evident in fossil record.• CONTRAST: MICROEVOLUTION• Speciation – Nonbranching evolution (transform a population enough for it to be designated a new species.) – Branching evolution (splits a lineage into two or more species)
The Origins of Species • Ernst Mayr – Studied the diversity of birds in New Guinea (1927) – Biological species concept • Species = “groups of interbreeding natural populations that are reproductively isolated from other such groups.” • Reproductive isolation blocks exchange of genes between species and keeps their gene pools separate.• Reproductive barriers between species • Zygote: fertilized egg • Pre-zygotic (factors that impede mating between species or hinder fertilization of eggs if mating is attempted) • Post-zygotic (mechanisms that operate should interspecies mating actually occur and form hybrid zygotes)
Mechanisms of Speciation• Allopatric Speciation – A population forms a new species while geographically isolated from its parent population.• Sympatric Speciation – A small population becomes a new species in the midst of a parent population
•Speciation occurs only withthe evolution of reproductivebarriers between the isolatedpopulation and its parentpopulation.•If speciation occurs duringgeographic separation, thenew species will not breedwith its ancestralpopulation, even if the twopopulations should comeback into contact.
Sympatric Speciation• Does not widely occur among animals but may account for over 25% of all plant species.
Notice how the hybrid bread wheat has a set of chromosomes from each of its ancestors: T. monococcum (AA), Triticum (BB), T. turgidum (AA BB), T. tauschii (DD)What can you notice about T.aestivum that might make it agood hybrid and the mostimportant wheat species today?
Relative Dating: Fossil Record Fossils chronologically ordered in rock layers
Meteor of thissize would havelowered thetemperature ofEarth due to theblocking of thesun byatmosphericdust. Theory: 65 million years ago a catastrophic event occurred killing off the dinosaurs and about ½ of the species inhabiting the Earth in a 10 million year time span.
The Origin of Life• Stage 1: Abiotic Synthesis of Organic Monomers – Amino Acids • Chains of nucleotides – Chains of DNA bases – Chains of RNA bases • Building blocks of protein – Sugars – Lipids – ATP
The Origin of Life• Stage 2: Abiotic Synthesis of Polymers – Monomers, such as amino acids, spontaneously fused together to form proteins.
The Origin of Life• Stage 3: Origin of Self-Replicating Molecules inheritance Ribozyme: catalytic RNA used to fuel RNA replication
The Origin of Life • Stage 4: Formation of Pre-cells – Molecular packages with some properties of life. – The gap between pre- cells and true cells is enormous! • Natural Selection
The origin of eukaryotic cells Endosymbiotic Theory– Membrane bound nuclear material– Organelles– More complex than prokaryotic cells– Ancestors to fungi, plants and animals
Concept MapSection 17-2 Evolution of Life Early Earth was hot; atmosphere contained poisonous gases. Earth cooled and oceans condensed. Simple organic molecules may have formed in the oceans.. Small sequences of RNA may have formed and replicated. First prokaryotes may have formed when RNA or DNA was enclosed in microspheres. Later prokaryotes were photosynthetic and produced oxygen. An oxygenated atmosphere capped by the ozone layer protected Earth. First eukaryotes may have been communities of prokaryotes. Multicellular eukaryotes evolved. Sexual reproduction increased genetic variability, hastening evolution.
Convergent Evolution• Process by which unrelated animals come to look like each other.• Dolphin• Penguin• Shark
Tempo of Evolution Spurts of relatively rapidSlow changeadaptations
Flowchart Section 17-4 Species that are Unrelated Related form in under under in in Similar Intense Inter- Small Different environments environmentalrelationshiops populations environments pressure can undergo can undergo can undergo can undergo can undergo Coevolution Convergent Punctuated Adaptive Extinction evolution equilibrium radiation
Classifying the Diversity of Life• Systematics – Reconstructing evolutionary history – Radioactive dating = tool – The study of biological diversity: past and present• Taxonomy – Identification, naming and classification of species – Pioneer: Carolus Linnaeus (1707-1778) • Binomial Nomenclature • Homo sapien
Hierarchical Classification Which step is more specific? Class or Genus? How is Domain Eukaryadifferent from Bacteria and Archaea?
Phylogeny •Evolutionary history of a species. •Tree is based on homologous structures, NOT analogous. •Two species will have more common nucleotide sequences based on how recently they branched from their common ancestor.