Evolution Evolution is the progressive change in a kind (not one individual, but a population) of organism over time. Specifically, evolution is the change over time of the genetic composition of populations. It is the process by which modern organisms have descended from ancient organisms. Evolutionary History James Hutton, regarded as the Father of modern Geology, developed (in 1795) the Theory of Uniformitarianism, the basis of modern geology and paleontology. Evolutionary History According to Hutton's work, certain geological processes operated in the past in much the same fashion as they do today, with minor exceptions of rates, etc. Thus many geological structures and processes cannot be explained if the earth is only 5000 years old. Evolutionary History British geologist Charles Lyell refined Hutton's ideas during the 1800s to include slow change over long periods of time. Scientists recognized that Earth is many millions of years old. Evolutionary History Lyells book Principles of Geology had profound effects on Charles Darwin and Alfred Wallace. Lamarck Jean-Baptiste Lamarck (1744 1829) a French naturalist just before Darwin. Lamarck Proposed by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species. Lamarcks Theory of Evolution: The Inheritance of Acquired Traits 1.All organisms have an innate tendency toward complexity and perfection. Ancestors of birds acquired an urge to fly, kept trying to fly, eventually their wings increased in size and now they are suited to flying. Lamarcks Theory of Evolution: The Inheritance of Acquired Traits 2.Organisms could alter the size or shape of particular organs by using their bodies in new ways. Birds try to use their front limbs to fly and they grew wings. If a winged animal did not use its wings they would decrease in size and disappear. Lamarcks Theory of Evolution: The Inheritance of Acquired Traits 3.Acquired characteristics could be inherited. If a bird spent its life trying to fly and developed larger wings, then its offspring would inherit larger wings. Lamarck Lamarck's theory of evolution is incorrect in several ways: He did not know how traits are inherited. He did not know that an organism's behavior has no effect on its inheritable characteristics. Lamarck However, Lamarck was one of the first to develop a scientific theory of evolution and realize that organisms are adapted to their environments. In this way, he paved the way for the work of later biologists. Charles Darwin ( ) Father of Evolution Darwin Darwin finally published On the Origin of Species in 1859 after he read Wallaces essay which summarized Darwins own thoughts on natural selection. Darwin Darwin saw things as descent with modification. By this he meant that the species of organisms inhabiting Earth today descended from ancestral species. Darwin This was due to 5 things he observed: 1.Exponential fertility 2.Stable population size 3.Limited resources 4.Individuals vary 5.Heritable variation. Darwin The 5 observations led to 3 inferences: 1.Struggle for existence 2.Non-random survival 3.Natural selection (differential success in reproduction). Darwin He proposed a mechanism for evolution called the Theory of Natural Selection the best adapted individuals in a population survive and produce offspring that are likewise well adapted and that evolution is a matter of variations and chance. Darwin Another way of understanding Natural Selection is that populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success). Summary of Darwin's Theory: Individual organisms in nature differ from one another and this variation is inherited. (Natural Variation). Summary of Darwin's Theory: Organisms in nature produce more offspring than can survive, and many of those that survive do not reproduce. (Over-reproduction). Summary of Darwin's Theory: Because more organisms are produced than can survive members of each species must compete for limited resources. (Struggle for Existence). Summary of Darwin's Theory: Because each organism is unique, each has different advantages and disadvantages in the struggle for existence. (Fitness Adaptations any inherited characteristic that enhance an organisms chance of survival, which also increases that organisms chance of reproducing). Summary of Darwin's Theory: Individuals best suited to their environment survive and reproduce most successfully (Survival of the Fittest). The characteristics that make them best suited to their environment are passed on to offspring. Summary of Darwin's Theory: Individuals whose characteristics are not as suited to their environment die or leave fewer offspring. (Natural Selection). Summary of Darwin's Theory: Species change over time. Over long periods, natural selection causes changes in the characteristics of a species, such as in size and form. New species arise, and other species disappear. (Speciation). Summary of Darwin's Theory: Species alive today have descended with modifications from species that lived in the past. (Descent with Modification). Summary of Darwin's Theory: All organisms on Earth are united into a single tree of life by common descent. (Common Descent). Darwin What Darwin needed was a mechanism to explain the theory of natural selection. How could favorable variations be transmitted to later generations. Ironically the mechanism was being figured out at almost the same time. Darwin The rediscovery of Mendels work along with the explosion of genetics in the 20 th century was the missing mechanism to support Darwins theory of natural selection. Darwinian theory supported by genetics is known as the modern synthesis. Adaptations An adaptation is an inherited characteristic that increases an organisms chance of survival. There are three main types of adaptations. Adaptations 1.Structural Adaptations: anatomical adaptation by an organism that promotes the fitness in its environment for example: wood peckers having a tough pointed beak for drilling holes in trees to get their prey or the shell of a turtle. Structural Adaptations Mimicry can be an example of a structural adaptation for example: a pueblan milksnake (harmless) looking like a coral snake (poisonous). This is also known as deceptive coloration. Pueblan Milksnake Eastern Coral Snake Lampropeltis triangulum Micrurus fulvius fulvius Structural Adaptations Aposmatic coloration can be an example of a structural adaptation a coral snake displaying bright colors to indicate that it is poisonous or the unrealistically brilliant colored eye opening of a red-eyed tree frog that provides just enough time to jump to another tree to avoid the startled predator. Red-Eyed Tree Frog Agalychnis challidryas Structural Adaptations Camouflage is a structural adaptation that enables a species to blend with their surroundings for example: a walking stick. This is also known as cryptic coloration. Walking stick Extatosoma tiaratum Adaptations 2.Behavioral Adaptations: results from the response of an organism to its external environment for example: frog mating songs or a squirrel storing acorns for the winter. Adaptations 3.Physiological Adaptations: adaptation with a chemical basis that is associated with an organisms function for example: the proteins that make a spiders web or the venom of a rattlesnake. Anatomy Homologous Structures: body parts which are similar in structure and/or in function for example: a humans arm, a cats forelimb, a whales flipper and a bats wing. Anatomy Vestigial Organs: body parts (structures) once useful for an organisms lifestyle, but now having no apparent function for example: the wings of a flightless bird, the hindlimb bones of a snake or whale, a humans appendix, etc. Anatomy The hindlimb bones of whales. Evidence of (Species) Evolution 3.Comparative Embryology: the study of developing organisms that shows a number of relationships not obvious in the adult organisms for example: pharyngeal pouches and tails as embryos in a variety of chordates. Comparative Embryology All vertebrates exhibit notochord during development. Comparative Embryology Evidence of (Species) Evolution 4.Comparative Biochemistry: Study of an organism on a biochemical level for example: the similarities of amino acids in hemoglobin of the blood of various vertebrates. Comparative Biochemistry Almost all living organisms use the same basic biochemicals: DNA, ATP, many identical enzymes, DNA triplet code, 20 amino acids, introns, and hypervariable regions. (Prokaryotes i.e. true bacteria (Domain Eukarya), do not have introns. This points to a long period of time since all living things shared common ancestory. Similarity of biochemistry is explained by descent from common ancestor. DNA base sequences differences in DNA between a number of organisms shows less difference the more closely related they are; for example, 2.5% difference between humans and chimpanzees but 42% difference between humans and lemurs. Amino acid sequences of cytochrome c show similarity between human and monkey, distance from human to duck and greater distance to Candida yeast. Data are understandable assuming humans and chimpanzees share a more recent common ancestor than do humans and lemurs, ducks, or yeast. Biochemical evidence is generally consistent with anatomical similarity of organisms. Evidence of (Species) Evolution 5.Genetic Evidence: for example: DNA similarities between people in certain parts of the world compared to people in other parts of the world. This is often considered a subset of comparative biochemistry. Evidence of (Species) Evolution 6.Direct Observations: observations of evolutionary changes that occur rapidly for example: penicillin-resistant bacteria, Industrial Melanism (see Peppered Moth Survey Lab). Population: a localized group of individuals belonging to the same species. Species: a group of organisms that can interbreed and produce fertile offspring. Speciation: the evolution of a new species. Review of Key Terms: Evidence of (Species) Evolution The Process of Speciation: It is theorized that different species developed because of: 1.Reproductive Isolation: the separation of species or populations so that they cannot interbreed and produce fertile offspring. Reproductive Isolation A.Temporal Isolation: different species of plants produce their flowers at different times so they are not cross-breeding. Temporal Isolation Chorus Frog--early spring Spring Peeper--late spring Am. Green Frog--early summer Bullfrog--late summer Reproductive Isolation B.Behavioral Isolation: different species of songbirds could interbreed, but dont as different songs are used to attract mates, so they do not end up cross-breeding. Reproductive Isolation C.Mechanical Isolation: mechanical barriers prevent the copulatory organs of closely related species from fitting together. It is theorized that different species developed because of: 2.Geographical Isolation: two populations of a species are separated by geographical barriers (such as rivers, mountains, canyons, etc) that prevent them from reproducing with one another. (A type of Reproductive Isolation). Evidence of (Species) Evolution The Process of Speciation: Geographical Isolation Habitat isolation: two organisms use different habitats within the same geographical area. This is exemplified by plants in a salt marsh vs. those that live in the same terrestrial area. Habitat Isolation Two species of garter snakes in the same Genus live in the same geographic areas, but one lives mainly in water, while the other is primarily terrestrial. Geographical Isolation Ring species provide unusual and valuable situations in which we can observe two species and the intermediate forms connecting them. Population Genetics: Individuals dont evolve, populations do. Gene pools: entire collection of genes among a population; populations evolve as the relative frequencies of different alleles (genes) change. Population Genetics: Natural selection acts on the phenotypes (physical traits) of a population, not directly on the genes. But it can change the relative frequencies of the alleles in a gene pool (population) over time. Population Genetics: Gene Flow: the loss or gain of alleles from a population due to the emigration or immigration of fertile individuals, or the transfer of gametes between populations. This reduces the differences between populations. Evolution of Species: It is theorized that different species developed because of: 4.Genetic Drift: in small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by chance, not selection. Genetic Drift Over time, a series of chance occurrences of this type can cause an allele to become common in a population. For example, Amish of Lancaster, Pennsylvania have a recessive allele causing dwarfism and higher proportion of polydactylism (1-in- 14 compared to 1-in-1,000). Genetic Drift Generation Generation Genetic Drift There are two common types of genetic drift: 1.The Founder Effect and 2.The Bottleneck Effect. Genetic Drift A.The Founder Effect: Where individuals may not be representative of the population they came from, yet start a new population where their phenotypes come to be expressed frequently. Founder Effect The new Atlantic population of Scorpaenidae Lionfish (Pterois volitans ), may have originated from only 10 individuals Genetic Drift B.The Bottleneck Effect: Disasters such as earthquakes, floods or fires may reduce the size of a population drastically, killing victims rather unselectively. Bottleneck Effect The result is that the small surviving population is unlikely to be representative of the original population in its genetic makeup. Bottleneck Effect Populations subjected to near extinction (like Cheetahs) endure a bottleneck. Bottleneck Effect Northern Elephant Seal Reduced to 20 individuals in 1896 Now 30,000 individuals, with no detectable genetic diversity Evolution of Species: It is theorized that different species developed because of: 5.Non-Random Mating: inbreeding and assortive mating (both shift frequencies of different genotypes). Both homozygotes increase in frequency, but heterozygotes decrease. Sources of Genetic Variation: Mutation: change(s) in the DNA of an organism. This is the original source of genetic variation (raw material for natural selection). Provides new alleles. Seemingly harmful mutations can be source of variation for better adaptation to a new or changing environment. Sources of Genetic Variation: Genetic shuffling that takes place during meiosis prior to sexual reproduction. Both the independent assortment of chromosomes during meiosis and the possibilities of crossing over. Population Genetics: Natural Selection on Single-Gene Traits: when there are only two possible phenotypes, natural selection can lead to changes in allele frequency which dont match typical expectations determined by punnett squares. Population Genetics: Natural Selection on Polygenic Traits: polygenic traits are those controlled by more than one set of genes. The phenotypes displayed by these traits often are displayed in a normal distribution, also known as a bell-shaped curve. Population Genetics: When there are more than two variations of possible phenotypes, natural selection causes shifts in the distribution of traits. There are three ways natural selection can effect the distribution of phenotypes. Three ways natural selection can effect the distribution of phenotypes: 1.Directional Selection: the entire curve shifts as the character trait changes. Directional selection: Occurs when one extreme of the distribution has an adaptation that could become favorable. When an environmental change or species migrate the new environment favors the extreme phenotype and the population evolves. Directional selection: For Example: woodpeckers that have shorter-lengthed beaks struggling to compete with woodpeckers that have longer- lengthed beaks leading to the natural selection of the woodpeckers with longer- lengthed beaks. Directional selection: Directional Selection: the entire curve shifts as the character trait changes. Industrial melanism and bacteria becoming antibiotic resistant are other examples of directional selection. Three ways natural selection can effect the distribution of phenotypes: 2.Stabilizing Selection: the distribution curve narrows as individuals in the middle of the distribution are favored. Stabilizing Selection: Average phenotypes (individuals) are favorable and extremes are not. Operates most of the time in most populations. Stabilizing Selection: Limits evolution as allele frequencies remain constant and the average individuals continue to dominate the population. Stabilizing Selection: For example: larger spiders are easily seen and eaten by predators. While smaller spiders find it difficult to find food. Therefore, average-sized spiders are favored by natural selection. Stabilizing Selection: Stabilizing Selection: the distribution curve narrows as individuals in the middle of the distribution are favored. Three ways natural selection can effect the distribution of phenotypes: 3.Disruptive Selection: the distribution curve begins to split in as the extremes are favored over the average phenotypes. (Also known as Diversifying Selection). Disruptive Selection: Two opposite phenotypes are favored and the average phenotype is not. Two subpopulations begin to form. If these subpopulations do not interbreed they can form two distinct species. Disruptive Selection: For example: in a beach environment light- colored limpets are favored against light- colored rocks and dark-colored limpets are favored against a dark-colored background. Intermediate-colored limpets are not favored on either background and are eaten by birds. As the light- and dark-colored limpets continue to survive in slightly different areas they will interact less and may become two separate species. Disruptive Selection: Disruptive Selection: the distribution curve begins to split in as the extremes are favored over the average phenotypes. (Also known as Diversifying Selection). Hardy-Weinberg Principle: The Hardy-Weinberg Principle states that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change. This state of unchanging allele frequencies is known as genetic equillibrium. Hardy-Weinberg Principle: Five conditions required to maintain genetic equilibrium (limit evolution of a population): 1.There must be random mating, in other words all individuals have the opportunity to produce offspring rarely happens in nature. Five conditions required to maintain genetic equilibrium (limit evolution of a population): 2.There must be a large population size. Genetic drift has less effect on large populations than on smaller populations. Five conditions required to maintain genetic equilibrium (limit evolution of a population): 3.There must not be movement of individuals into or out of the population no immigration or emigration. Five conditions required to maintain genetic equilibrium (limit evolution of a population): 4.There must not be genetic mutations no new alleles can be introduced. Five conditions required to maintain genetic equilibrium (limit evolution of a population): 5.There must not be natural selection meaning no traits are favored over other traits. Hardy-Weinberg Equation: p=frequency of one allele (A); q=frequency of the other allele (a); p + q = 1.0 (p = 1 - q & q = 1 - p) P 2 =frequency of AA genotype; 2pq=frequency of Aa plus aA genotypes; q 2 =frequency of aa genotype; p 2 + 2pq + q 2 = 1.0 Hardy-Weinberg Equation: p + q = = 1.0 p = 1 q 0.7 = 1 0.3 q = 1 p 0.3 = 1 0.7 Hardy-Weinberg Equation: p 2 = frequency of AA genotype; 2pq = frequency of Aa plus aA genotypes; q 2 = frequency of aa genotype; Hardy-Weinberg Equation: p 2 + 2pq + q 2 = 1.0 (0.7) 2 + 2(0.7)(0.3) + (0.3) 2 = = 1.0 Hardy-Weinberg Equation: The five conditions of the Hardy- Weinberg principle are rarely met, so allele frequencies in the gene pool of a population do change from one generation to the next, resulting in evolution. We can now consider that any change of allele frequencies in a gene pool indicates that evolution has occurred. Hardy-Weinberg Equation: The Hardy-Weinberg principle proposes those factors that violate the conditions listed cause evolution. A Hardy-Weinberg equilibrium provides a baseline by which to judge whether evolution has occurred. Hardy-Weinberg Equation: Hardy-Weinberg equilibrium is a constancy of gene pool frequencies that remains across generations, and might best be found among stable populations with no natural selection or where selection is stabilizing. Patterns of Evolution: Adaptive Radiation: the process by which a single species or small group of species evolves into several different forms that live in different ways. This is also referred to as divergent evolution. Patterns of Evolution: Divergent Evolution: This is what Darwin saw on the Galapagos Islands with finches that contained far greater variation, 13 different-sized finches with different bills adapted to particular food- gathering methods. Divergent Evolution: Patterns of Evolution: Convergent Evolution: the process by which unrelated organisms independently evolve similarities when adapting to a similar environment. Dolphins and sharks both having adaptations (flippers and fins) for swimming. Convergent Evolution: Birds, insects and bats all having the adaptation (wings) of being capable of flying. Structures that are not similar but function in similar ways are called analogous structures. Analogous Structures Bird Beak Squid Beak Convergent Evolution: Two similar species filling similar ecological roles (niches) having evolved in distinctly different parts of the world. Sugar glider AUSTRALIA NORTH AMERICA Flying squirrel Figure 22.17 Patterns of Evolution: Coevolution: the process by which two species evolve in response to changes in each other This is also known as mutual adaptation or mutualism. Coevolution: A clown fish living with sea anemones. Insects that pollinate flowers. Bacteria Nodules on the roots of plants (legumes). Patterns of Evolution: Punctuated Equilibrium: a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change. This pattern often follows periods of mass extinction. Punctuated Equilibrium: Tempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the non- gradual appearance of species in the fossil record. Patterns of Evolution: The fossil record appears to support this: Constant Sudden Changes Time Change Punctuated Equilibrium Patterns of Evolution: Darwin, however, explained evolution as a gradual accumulation of variations Time Change Gradualism Patterns of Evolution: Mass Extinctions: extinctions (the death of an entire species) occur all the time. More so now due to man than by natural events. Mass Extinctions: However, in geological history there have been periods of mass extinction, caused by natural events, where numerous species disappear which greatly effect the survival of the species that remain leading to explosions of evolution as these species adapt to the new circumstances. Mass Extinctions: Five mass extinctions in fossil record define end of: 1.Ordovician 2.Devonian 3.Permian 4.Triassic 5.Cretaceous Mass Extinctions: Following extinctions, remaining groups expand to fill habitats vacated by extinct species. Marine animal fossil record indicates mass extinctions occur every 26 million years; corresponds to movement of solar system within Milky Way galaxy. The Origin of Species The Origin of Species. Macroevolution: the origin of new taxonomic groups. Macroevolution: Speciation: the origin of new species. A.Anagenesis (phyletic evolution): accumulation of heritable changes. Macroevolution: Speciation: the origin of new species. B.Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity). Macroevolution: Reproductive Isolation: Comparing Dating Methods: Relative Dating Can determine Is performed by Drawbacks Absolute Dating Comparing Relative and Absolute Dating of Fossils Imprecision and limitations of age data Difficulty of radioassay laboratory methods Comparing depth of a fossils source stratum to the position of a reference fossil or rock Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen Age of fossil with respect to another rock or fossil (that is, older or younger) Age of a fossil in years Relative Dating: Absolute Dating: Radiometric dating; age using half-lives of radioactive isotopes. Isotopes each have particular half-life or time it takes for half of isotope to decay and become nonradioactive. Carbon-14 ( 14 C) used to date organic matter; half decays to 14 N each 5,730 years; limited to about last 50,000 years. Half of potassium-40 ( 40 K) decays to argon-40 ( 40 Ar) each 1.3 million years; estimates age of younger rocks. Uranium-238 decays to lead-207; estimates age of older rocks. Earths History Summary Earths history up to 543 million years ago (Almost 90% of the Earths history occurred during this time.) The Earth forms. One-celled organisms (prokaryotes) arise. Eukaryotic cells evolve. The atmosphere becomes enriched in oxygen. Complex multicellular organisms, including the first animals evolved. How did life Begin? A few organic molecules is a long way from a living cell. The leap from non-life to life is the greatest gap in scientific theories of Earths early history. As material circulated through the apparatus, Miller and Urey periodically collected samples for analysis. They identified a variety of organic molecules, including amino acids such as alanine and glutamic acid that are common in the proteins of organisms. They also found many other amino acids and complex, oily hydrocarbons. Miller and Urey set up a closed system in their laboratory to simulate conditions thought to have existed on early Earth. A warmed flask of water simulated the primeval sea. The strongly reducing atmosphere in the system consisted of H 2, methane (CH 4 ), ammonia (NH 3 ), and water vapor. Sparks were discharged in the synthetic atmosphere to mimic lightning. A condenser cooled the atmosphere, raining water and any dissolved compounds into the miniature sea. Organic molecules, a first step in the origin of life, can form in a strongly reducing atmosphere. Laboratory experiments simulating an early Earth atmosphere Have produced organic molecules from inorganic precursors, but the existence of such an atmosphere on early Earth is unlikely Electrode Condenser Cooled water containing organic molecules H2OH2O Sample for chemical analysis Cold water Water vapor RESULTS EXPERIMENT CONCLUSION Precambrian Time Archaen Eon: In the early 1950s two scientists, Stanley Miller and Harold Urey, created an experiment meant to mimic early Earth environment and see if they could create organic molecules (Oparins Hypothesis). Several amino acids were formed, but this experiment has been shown to be set up atmospherically incorrectly. However, Miller did an experiment in 1995 that actually produced cytosine and uracil, 2 of the bases found in RNA. How did life Begin? The first organic compounds on Earth may have been synthesized near submerged volcanoes and deep-sea vents. How did life Begin? Some of the organic compounds from which the first life on Earth arose May have come from space (extraterrestrial). Carbon compounds Have been found in some of the meteorites that have landed on Earth The possibility that life is not restricted to Earth Is becoming more accessible to scientific testing How did life Begin? Abiotic Synthesis of Polymers: Small organic molecules Polymerize when they are concentrated on hot sand, clay, or rock How did life Begin? Scientists do know that about 200 to 300 million years after Earth cooled enough to carry liquid water, cells similar to modern bacteria were common. Some scientists theorize that RNA nucleotides could have come together and formed RNA. Some forms of RNA are able to duplicate themselves. These could have led to DNA. The RNA World: RNA molecules called ribozymes have been found to catalyze many different reactions, including Self-splicing Making complementary copies of short stretches of their own sequence or other short pieces of RNA Ribozyme (RNA molecule) Template Nucleotides Complementary RNA copy 3 5 5 How did life Begin? Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection When did life Begin? Precambrian Time Archaen Eon: One-celled organisms known as prokaryotes arise, the ancestors of present-day bacteria and cyanobacteria. All life during the more than one billion years of the Archaean was bacterial. Stromatolites colonies of early photosynthetic cyanobacteria that show the earliest evidence of life on Earth. Precambrian Time Proterozoic Eon: 2.5 billion to 543 million years ago. Atmospheric oxygen increases as a byproduct of photosynthetic bacteria. Precambrian Time Proterozoic Eon: While the increase in atmospheric oxygen was a global catastrophe as it limited a lot of bacterial life, it allowed for the evolution of eukaryotes (cells that posses a cellular nucleus, a nuclear membrane and membrane-bound organelles). Precambrian Time Proterozoic Eon: Evolution of eukaryotes: Endosymbiotic Theory Aerobic bacteria Ancient Prokaryotes Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Primitive Photosynthetic Eukaryote Chloroplast Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Plants and plantlike protists Animals, fungi, and non-plantlike protists