Evolution and the Diversity of Life Classification of Life Chapters 13, 14 part of 17 Arizona State Standards S3C4PO1 S3C4PO2 S3C4PO3 S3C4PO4 S3C4PO5 S3C4PO6 What is meant by the word “theory”? Theory Theories embody the highest level of certainty for comprehensive ideas in science. Thus, when someone claims that evolution is "just a theory," it's roughly equivalent to saying that the proposition that the Earth circles the sun rather than vice versa is "just a theory." What is Evolution? In the simplest biological terms evolution is defined as change over time. However, it is much more than that. The Idea of Fixed Species – The Greek philosopher Aristotle held the belief that species are fixed and do not change over time. Lamarck and Evolutionary Adaptations – In the mid-1700s, the study of fossils began to take form as a branch of science. – Naturalist Georges Buffon • Suggested that the Earth might be older than some had previously though. • Observed similarities between fossils and living species. Lamarck and Evolutionary Adaptations • Jean-Baptiste Lamarck suggested that organisms evolved by the process of adaptation. • Also suggested some erroneous ideas, such as the inheritance of acquired characteristics. Darwin • Who was Charles Darwin? • Charles Darwin first published an explanation of how species changed over time, or evolved. • Darwin argued that contemporary species arose from ancestors • Through a process of “descent with modification,” with natural selection as the mechanism. How did he explain evolution? • Natural Selection: Occurs in natural populations when organisms with certain traits pass those traits on to the next generation. • The following are required for natural selection to take place. 1. Organisms can change over generations. 2. Individuals with certain heritable traits produce more surviving offspring than others. 3. The result of natural selection is evolutionary adaptation. Seahorse Camouflage Change Over Time Evidence for evolution The Evidence Evidence of evolution comes from wide range of areas. 1. Fossils • In biological terms a fossil can be defined as evidence of an organism that lived some time in the past. • Are often found in sedimentary rocks. Fossilization Process • Few organisms become fossils. • Organisms usually have to be buried in mud, sand or clay soon after they die. • Most fossils are found in sedimentary rock. • These rocks form at relatively low temperatures and pressures that may prevent damage to the organism. • Metamorphic rock and igneous rock undergo very physically demanding transformations that can incinerate and destroy organisms, which is why they do not typically contain fossils. Fossils The fossil record • Is the ordered sequence of fossils as they appear in rock layers. • Reveals the appearance of organisms in a historical sequence. • Fits with other evidence of evolution. • Paleontologists study fossils Fossils History of Paleontology • Paleontology began in the late 17th century when English naturalist Robert Hooke examined fossils of marine creatures from England. • Charles Darwin used the fossil record to form his explanation of the theory of evolution in the 1830’s. Fossils Fossils show a succession from very simple forms early in the fossil record to much more complex forms that appear much later in the fossil record. Fossils Fossils show multiple examples of transitional forms. Fossils Fossils and Geological Time • Scientists will date the rocks in an attempt to determine the age of the fossil. Two ways to do this: • Relative dating: When you compare the depth of the layer of rock the fossil was formed in relative to other layers of rock. • Radiometric dating: Uses isotopes. Fossils Relative Dating aka Law of Superposition • Relative dating uses layers to determine age by order of appearance. • Relative dating will not give you a specific age in years, just relative to the layers above and below the fossil. • Compare rock layers to layers of clothing in your laundry hamper…Oldest on the bottom (unless disturbed). Fossils Radiometric Dating • Technique involves using radioactive isotopes, which are atoms with unstable nuclei that break down (decay) over time, giving off radiation. • Most fossils cannot be directly radiometrically dated. • Most dates are for volcanic or igneous rocks, or metamorphic rocks that are closely associated with sedimentary rocks. 2. Biogeography • Is the study of the geographic distribution of species. • First suggested to Darwin that today’s organisms evolved from ancestral forms. • Many examples from biogeography support evolutionary theory. Island Biogeography • Theory of Island Biogeography – Islands have fewer species than continents – The smaller the island, the fewer the species • Adaptive Radiation: – The process that occurs when a species enters a new habitat that has unoccupied niches and evolves into a group of new species, each adapted to one of these niches. • Ecological Island: – An area that is biologically isolated so that a species occurring within the area rarely mixes with any other population of the same species. Convergent and Divergent Evolution • Divergent – Organisms with the same ancestral genetic heritage migrate to different habitats and evolve into species with different external forms and structures, but continue to use the same type of habitats • Ex) Ostrich • Convergent – The process by which species evolve in different places of times and, although they have different genetic heritages, develop similar external forms and structures as a result of adaptation to similar environments • Ex) shapes of sharks 3. Comparative Anatomy A. Homologous Structures – structural features with a common evolutionary origin – shared by related species. Although used for such different functions as throwing, swimming, and flying, the same basic structural plan is evident in them all. In each case, the bone shown in color is the radius. Comparative Anatomy B. Analogous Structures – Structural features which serve the same function in different species, but they evolved independently. Example: Butterfly wings, Bat wings Bird wings Comparative Anatomy C. Vestigial Structures – Humans have a vestigial tailbone. Vestigial toes in the horse. Vestigial limbs in whales and snakes. 3b. Structural Adaptations A. Mimicry: A structural adaptation that protects an organism by copying the appearance of another species. – Example: Gopher snake B. Camouflage – A structural adaptation that allows an organism to blend in with its environment. – Example: Snowshoe hare Gopher Snakes? The one on the left is a rattlesnake, the one on the left is a gopher snake. Showshoe Hare Summer Winter Are ALL adaptations structural? • List as many behavioral adaptations as you can think of. Are ALL adaptations structural? • No! Some adaptations are behavioral adaptations • Moving in large groups is one example; it helps protect the members of the group from predators. • Other types of behavioral adaptations: • Nocturnal • Arboreal • Burrowing 4. Comparative Embryology Embryology – Early embryos of very different organisms closely resemble each other. 5. Molecular biology Biochemistry - The biochemistry of a bat is much closer to that of a whale, rather than a bird. Not expected unless bat and whale have a more recent common ancestor than bat and bird, but evolution predicts this. 5. Biochemistry Check for Understanding 1. What is the difference between a scientific theory and a laymen’s definition of the word theory? 2. What are structural adaptations and how do they support the theory of evolution? 3. What are examples of behavioral adaptations and how do they support evolution? 4. How does the fossil record support the theory of evolution? 5. What is the different between homologous, analogous and vestigial structures? How do each of these support the theory of evolution? 6. How does embryology support the theory of evolution? 7. How does biochemistry support the theory of evolution? Natural Selection • Natural selection is the mechanism for evolution. • It only acts on populations. • It changes the frequency of genes in a population – not in an individual. What traits are usually selected? • Traits that allow the organism to survive and reproduce. Question • Do Individuals Evolve? NO!!! But… Why? http://evolution.berkeley.edu/evolibrary/article//bergstrom_02 Peppered Moth Example • Originally White • Now more black than white • Causes – Industrial Pollution • Soot covered trees – Industrial Melanism http://www.amphi.com/~crobson/pepperMoths.swf How does natural selection happen? Evolution only occurs when there is a change in gene frequency within a population over time. Vocabulary The total number of genes present in a population is called the gene pool of that population. Vocabulary The frequency of an allele for a specific trait is called the allelic frequency. Vocabulary The genetic equilibrium of any population is when the allelic frequency if alleles remains the same over time. Question • If a population is in a state of genetic equilibrium is it evolving? NO!!! Microevolution as Change in a Gene Pool – Microevolution is defined as • A generation-to-generation change in a population’s frequencies of alleles. – Hardy-Weinberg equilibrium • Describes a non-evolving population that is in genetic equilibrium. • We will discuss this equilibrium in more detail later. Mechanisms of Microevolution The main causes of microevolution are • Mutations. • Genetic drift. • Gene flow. • Natural selection. Ways to Change Genetic Equilibrium 1. Mutation – Can be caused be different factors, environmental or random chance. Ways to Change Genetic Equilibrium 2. Genetic Drift – Changes in allelic frequencies due to chance events. Ex: The founder effect • Explains the relatively high frequency of certain inherited disorders among some populations. Ex:The bottleneck effect • Results from a drastic reduction in population size. • Usually results in a reduction in variation Ways to Change Genetic Equilibrium 3. Movement – Can be into or out of the population. Also referred to as gene flow. Darwinian Fitness • Is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals. Natural Selection • What about natural selection? • There are 3 types 1. Stabilizing – Where the average trait is selected for. This is often mistaken for "no selection". A real-life example is that of birth weight of human babies. Natural Selection • Directional - one extreme trait of the frequency distribution is favored, so the distribution in the subsequent generation is shifted from where it was in the parental generation, towards that of the favored trait. This is what is usually thought of as natural selection. A real-life example would be the evolution of long bills in woodpeckers. Natural Selection • Disruptive - both extreme traits are favored at the expense of intermediate varieties. For example very dark and very light moths are selected over medium shaded moths. http://www.ibri.org/Books/Pun_Evolution/Chapter1/1.4.htm Hardy Weinberg Table 1. Frequencies of Alleles, Genotypes and Appearances for Students in Class Appearance & Genotype Frequencies (decimal) W w W2 2Ww w2 Table 2. Frequencies of Alleles/Genotypes and Appearances for 4 Class Groups Appearance & Genotype Group 1 Frequencies Group 2 Frequencies Group 3 Frequencies Group 4 Frequencies W w W2 2Ww w2 The Hardy Weinberg Formula • Is a mathematical representation of a gene pool. • Adds up all of the genotypes in a population. Alleles in a gene pool • Occur in certain frequencies. • Can be symbolized by p for the relative frequency of the dominant allele in the population and q for the frequency of the recessive allele in the population. Population Genetics and Health Science – The Hardy-Weinberg formula can be used to calculate the percentage of a human population that carries the allele for a particular inherited disease. Macroevolution and the Diversity of Life • Macroevolution encompasses the major biological changes evident in the fossil record. • Includes the formation of new species. – How does this relate to microevolution? Speciation • The evolution of new species is called speciation. • Is the focal point of macroevolution. • May occur based on two contrasting patterns. 1. In nonbranching evolution, a population transforms but does not create a new species. 2. In branching evolution, one or more new species branch from a parent species that may continue to exist. What is a species??? What Is a Species? – The biological species concept defines a species as • A population or group of populations whose members have the potential to interbreed and produce fertile offspring. Galápagos Sea Lion Galápagos Tortoise How does speciation occur? • Speciation occurs only when there are reproductive barriers between the isolated population and its parent population. 1. Reproductive isolation – When groups of individuals can no longer mate and produce fertile offspring. 2. Geographic isolation – when a physical barrier divides a population. Mechanisms of Speciation – A key event in the potential origin of a species occurs when a population is somehow severed from other populations of the parent species. – The two modes of speciation are • Allopatric speciation. • Sympatric speciation. Allopatric Speciation – Geologic processes • Can fragment a population into two or more isolated populations. • Can contribute to allopatric speciation. Grand Canyon Galápagos Islands Overview Galápagos Marine Iguana Sympatric Speciation – Sympatric speciation occurs if a genetic change produces a reproductive barrier between mutants and the parent population. • Polyploidy, a mechanism of sympatric speciation, was first observed by Hugo de Vries. Punctuated Equilibrium Is a contrasting model of evolution. • States that species most often diverge in spurts of relatively sudden change. • Accounts for the relative rarity of transitional fossils. Check for Understanding 1. What is natural selection? 2. List and describe the three types of natural selection. 3. How does natural selection explain evolution? 4. What is speciation and how does it occur? Question • Does evolution explain the origin of life? Where do living things come from? • One theory held in the past is referred to as Spontaneous generation. This theory held that nonliving material can produce life. • Fancesco Redi disproved this theory with an experiment now known as the Redi Experiment. This experiment helped to disprove the spontaneous generation of large organisms, but not microorganisms. Redi’s (1626-1697) Experiments Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat The Origin of Life • Likewise, Louis Pasteur designed an experiment to disprove the spontaneous generation of microorganisms. Louis Pasteur (1822-1895) Pasteur's Problem • Hypothesis: Microbes come from cells of organisms on dust particles in the air; not the air itself. • Pasteur put broth into several special S-shaped flasks • Each flask was boiled and placed at various locations Pasteur's Experiment - Step 1 • S-shaped Flask • Filled with broth • The special shaped was intended to trap any dust particles containing bacteria Pasteur's Experiment - Step 2 • Flasks boiled • Microbes Killed Pasteur's Experiment - Step 3 • Flask left at various locations • Did not turn cloudy • Microbes not found • Notice the dust that collected in the neck of the flask Pasteur's Experimental Results Question: So what do Pasteur's experimental results mean? So what now? The Theory of Biogenesis • Pasteur’s S-shaped flask kept microbes out but let air in. • Proved microbes only come from other microbes (life from life) - biogenesis Figure 1.3 The Origin of Life • Biogenesis – All living organisms must come from other living organisms. • Simple Prokaryotic cells were probably the first cells and over time the would have evolved into Eukaryotic cells. Evidence for this is seen in mitochondrial DNA. Check Your Understanding 1. What are the major eras and events that occurred during each? 2. What is spontaneous generation? 3. How was spontaneous generation disproved for large organisms? 4. How was spontaneous generation disproved for microorganisms? 5. What is biogenesis? 6. Describe the evolutionary process of cells and please include evidence for this theory. Geological Time The History of Life Fossils and Geological Time • Geological Time – determined by the fossil record. • The best current estimate for the age of the earth is 4.6 billion years. Types of Fossils 1. Trace Fossils 2. Molds 3. Amber-preserved or Frozen Fossils 4. Petrified / Permineralized Fossils 5. Casts Figure 14.16 Trace Fossils • Are the markings or evidence of animal activities. • They include footprints, trails, and burrows. Trace Fossil Example • Laoporus tracks • Coconinio Sandstone, Arizona • Paleozoic Era • Sold for $2,950 Molds • When an organism is buried, it can decay, leaving an empty space in the rock that is the exact shape of the organism. Mold Fossil Example • Marine fossils are commonly buried in shale, limestone, and sandstone. • Hard-shelled invertebrates • Early vertebrates Amber-preserved or Frozen Fossils • Sometimes an entire, intact organism can be found frozen in ice or preserved in fossilized tree sap, such as amber. • These types of fossils are rare, but valuable to science because even the most delicate parts of the organism are usually preserved. Amber Fossil Example • Prehistoric Praying Mantis with its dinner – an ant! • Left foreleg raised ready to strike • La Toca Mines, Dominican Republic Petrified or Permineralized Fossils • The hard parts of organisms are sometimes penetrated and replaced by minerals, atom – for – atom. • When the minerals harden, an exact stone copy of the original organism is produced. • Empty spaces in original organism are filled in by minerals. Petrified Fossil Example • National Historic Landmark in Saratoga Springs • Petrified Sea Gardens • Ocean-reef 500 million-years old Casts • When a mold of an organism is created, it often becomes filled by minerals in the surrounding rock, producing a replica of the original organism. Cast Fossil Example • Ammonite • Era – Mesozoic • Epoch – Cretaceous • 135 million years old Check Your Understanding 1. 2. 3. 4. What are fossils? What does a paleontologist study? How are fossils formed? Why are fossils formed in sedimentary rocks? 5. Discuss conditions necessary for fossilization. 6. How are fossils dated? 7. Can you name and describe the 5 types of fossils? Fossils, Geological Time & Biology • Life began in the Precambrian era. • Fish and Reptiles developed during the Paleozoic era. • Dinosaurs were seen in the Mesozoic era. • We currently live in the Cenozoic era. The Geologic Record Fossils, Geological Time & Biology • Life began in the ______________ era. • Fish and Reptiles developed during the ______________ era. • Dinosaurs were seen in the ______________ era. • We currently live in the ______________ era. The Geologic Record Fossils, Geological Time & Biology • Life began in the Precambrian era. • Fish and Reptiles developed during the Paleozoic era. • Dinosaurs were seen in the Mesozoic era. • We currently live in the Cenozoic era. The Geologic Record Table 14.1 Study! • Study your timeline notes and the timeline in the book! You will need to know all of the eras and periods for the unit exam! Do you remember the major periods? If so write them on your page. If not look them up and write them down. Mass Extinctions and Explosive Diversifications of Life – The fossil record reveals an episodic history, • With long, relatively stable periods punctuated by briefer intervals when the turnover in species composition was much more extensive. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings – Extinction is inevitable in a changing world and occurs all the time. • However, extinction rates have not been steady. – Extinctions typically eliminate various species of organisms • And are followed by explosive diversifications of organisms. How many extinctions have happened? Are we in an extinction now? Classifying the Diversity of Life – Systematics • Is the study of the diversity and relationships of organisms, both past and present. – Taxonomy • Is the identification, naming, and classification of species. Systems of Classification • Classifying is a way of organizing information • Classify = to put objects or ideas into groups on the basis of similarity • Taxonomist – scientists who study classification • Phylogony – evolutionary history of an organism. • Why have a system of naming? – Local or common names of species can be different – Different languages name species differently Aristotle first system of classification • Two groups: All organisms as plants or animals • Each animal according to where it lived – Land – Water – Air • Each plant according to – Size – Structure Carolus von Linneaus mid-1700’s • Determined levels of classification – He used similarities in structure to determine relationships among organisms. • Binomial Nomenclature • Two-word naming system LATIN! – Genus • Noun, Capitalized, Underlined – species • Descriptive, Lower Case, Underlined Hierarchical Classification – The taxonomic hierarchy: – Write them down from largest (Domain) to smallest – Can you think of a mnemonic device? Write it down Classification and Phylogeny – The goal of classification is to reflect phylogeny, the evolutionary history of a species. Sorting Homology from Analogy – Homologous structures • What are they? • Are one of the best sources of information about phylogenetic relationships. – Convergent evolution • Involves superficially similar structures in unrelated organisms based on natural selection. – Analogy • Is similarity due to convergence. Molecular Biology as a Tool in Systematics – Molecular systematics • Compares DNA and amino acid sequences between organisms. • Can reveal evolutionary relationships. The Cladistic Revolution – Cladistics • Is the scientific search for clades, • Clades are distinctive branches in the history of life. – Cladistics • Has ______________ traditional classification of some organisms. Arranging Life into Kingdoms: A Work in Progress – Linnaeus designed a two-kingdom system of classification, • Which was replaced by a five-kingdom system in the mid-20th century. • Now we use a six-kingdom system, which may change again! Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings – In the late 20th century, • Molecular studies and cladistics led to the development of a three-domain system. Classification Schemes Tools! • Dichotomous Key: Allows people to identify organisms in the real world based on a series of two choices at each step. Identify This Tree http://www.uwsp.edu/cnr/leaf/Treekey/tkframe.htm Dichotomous Key Activity! • Are you ready to try this in more detail?