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EVOLUTION Name_______________________ • Early scientists proposed ideas about evolution. • Evolution is • A species is • There were many important naturalists in the 18th century. • Linnaeus: • Buffon: species shared ancestors rather than arising separately • E. Darwin: more-complex forms developed from less-complex forms • Lamarck: • Theories of geologic change set the stage for Darwin’s theory. • There were three theories of geologic change.---Catastrophism---Gradualism--uniformitarianism • The theory of catastrophism states that • Gradualism • The theory of uniformitarianism states that • Fossils • Uniformitarianism is the prevailing theory of geologic change. • Darwin observed differences among island species. Darwin’s voyage provided insight on evolution. • Variation • – Galápagos tortoises that live in areas with tall plants have long necks and legs. – Galápagos finches that live in areas with hard-shelled nuts have strong beaks. An adaptation – Species are able to adapt to their environment. – Adaptations can lead to genetic change in a population. • Darwin observed fossil and geologic evidence supporting an ancient Earth. • Darwin found fossils of extinct animals that resemble modern animals. • Darwin found fossil shells high up in the Andes mountains. • He saw land move from underwater to above sea level due to an earthquake. 1 • Darwin extended his observations to the evolution of organisms. • • Darwin noticed a lot of variation in domesticated plants and animals. • Artificial selection • Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals. • Natural selection explains how evolution can occur. • Heritability • There is a struggle for survival due to overpopulation and limited resources. • Darwin proposed that adaptations arose over many generations. • Natural selection explains how evolution can occur. • There are four main principles to the theory of natural selection. - - - - • Natural selection acts on existing variation. • Natural selection can act only on traits that already exist. • Structures take on new functions in addition to their original function. • A population is • Fitness • Evidence of common ancestry among species comes from many sources. • • Fossils in older layers are more primitive than those in the upper layers. • Biogeography is • The study of geography provides evidence of evolution. • – island species most closely resemble nearest mainland species – populations can show variation from one island to another Embryology provides evidence of evolution. – • identical larvae, different adult body forms --similar embryos, diverse organisms The study of anatomy provides evidence of evolution. 2 – Homologous structures – Homologous structures are evidence of a common ancestor. – Analogous structures – Analogous structures are not evidence of a common ancestor. • Structural patterns are clues to the history of a species. • Vestigial structures are • Ostrich wings are examples of vestigial structures. • Fossils provide a record of evolution. • Paleontology • Paleontology provides evidence to support evolution. • Molecular and genetic evidence support fossil and anatomical evidence. • Two closely-related organisms will have similar DNA sequences. • Pseudogenes are sequences providing evidence of evolution. – no longer function --carried along with functional DNA --can be clues to a common ancestor • Evolution unites all fields of biology. • Scientist from any fields contribute to the understanding of evolution. • The basic principles of evolution are used in many scientific fields. • A population shares a common gene pool. • Genetic variation in a population increases the chance that some individuals will survive. • • Phenotypic variation is necessary for natural selection. • Genetic variation is stored in a population’s gene pool. – • --allele combinations form when organisms have offspring Allele frequencies measure genetic variation. – • made up of all alleles in a population measures how common allele is in population --can be calculated for each allele in gene pool Genetic variation comes from several sources. • 3 – can form new allele -- can be passed on to offspring if in reproductive cells • Recombination forms new combinations of alleles. – usually occurs during meiosis -- parents’ alleles arranged in new ways in gametes • Hybridization is the crossing of two different species. – occurs when individuals can’t find mate of own species --topic of current scientific research • Populations, not individuals, evolve. Natural selection acts on distributions of traits. • A normal distribution graphs as a bell-shaped curve. – highest frequency near mean value Sketch the graph -- frequencies decrease toward each extreme value • Traits not undergoing natural selection have a normal distribution. • Natural selection can change the distribution of a trait in one of three ways. • Microevolution is evolution within a population. – observable change in the allele frequencies -- can result from natural selection – Natural selection can take one of three paths. Sketch the graphs – Directional selection favors phenotypes at one extreme. – Stabilizing selection favors the intermediate phenotype. – Disruptive selection favors both extreme phenotypes. • Natural selection is not the only mechanism through which populations evolve. Gene flow is the movement of alleles between populations. • Gene flow occurs when individuals join new populations and reproduce. • 4 • Low gene flow increases the chance that two populations will evolve into different species. • Genetic drift is a change in allele frequencies due to chance. • • It is most common in small populations. • A population bottleneck can lead to genetic drift. • – It occurs when an event drastically reduces population size. – The bottleneck effect is genetic drift that occurs after a bottleneck event. The founding of a small population can lead to genetic drift. – – • The founder effect is genetic drift that occurs after start of new population. Genetic drift has negative effects on a population. – less likely to have some individuals that can adapt – • Sexual selection occurs when certain traits increase mating success. • • – males produce many sperm continuously – females are more limited in potential offspring each cycle There are two types of sexual selection. – intrasexual selection: – intersexual selection: males display certain traits to females Hardy-Weinberg equilibrium describes populations that are not evolving. • Biologists use models to study populations. • Genotype frequencies stay the same if five conditions are met. • – very large population: no genetic drift – no mutations: no new alleles added to gene pool – no natural selection: all traits aid equally in survival --no emigration or immigration: no gene flow --random mating: no sexual selection Real populations rarely meet all five conditions. 5 – Real population data is compared to a model. --Models are used to studying how populations evolve. • The Hardy-Weinberg equation is used to predict genotype frequencies in a population. • Predicted genotype frequencies are compared with actual frequencies. – used for traits in simple dominant-recessive systems – must know frequency of recessive homozygotes • There are five factors that can lead to evolution. • Genetic drift • Gene flow • Mutations • Sexual selection • Natural selection • In nature, populations evolve. – expected in all populations most of the time --p2 + 2pq + q2 = 1 -respond to changing environments • The isolation of populations can lead to speciation. • Populations become isolated when there is no gene flow. – Isolated populations adapt to their own environments. – • Reproductive isolation can occur between isolated populations. – members of different populations cannot mate successfully • Speciation is • Populations can become isolated in several ways. • Behavioral barriers can cause isolation. – • -includes differences in courtship or mating behaviors Geographic barriers can cause isolation. – • called behavioral isolation -final step to becoming separate species called geographic isolation -physical barriers divide population Temporal barriers can cause isolation. – called temporal isolation -timing of reproductive periods prevents mating 6 • Evolution occurs in patterns. Evolution through natural selection is not random. • Natural selection can have direction. • The effects of natural selection add up over time. • Convergent evolution • Divergent evolution • Species can shape each other over time. • Two or more species can evolve together through coevolution. – evolutionary paths become connected • Coevolution can occur in beneficial relationships. • Coevolution can occur in competitive relationships. • Species can become extinct. -species evolved in response to changes in each other • • Background extinctions occur continuously at a very low rate. – • – usually affects a few species in a small area – caused by local changes in environment Mass extinctions are rare but much more intense. – destroy many species at global level – – • at least five mass extinctions in last 600 million years Speciation often occurs in patterns. • – theory proposed by Eldredge and Gould in 1972 – episodes of speciation occur suddenly in geologic time – followed by long periods of little evolutionary change – revised Darwin’s idea that species arose through gradual transformations • 7 – ancestral species diversifies into many descendent species – descendent species usually adapted to wide range of environments • Specific environmental conditions are necessary in order for fossils to form. • Fossils can form in several ways. • Permineralization occurs when minerals carried by water are deposited around a hard structure. • A natural cast forms when flowing water removes all of the original tissue, leaving an impression. • Trace fossils record the activity of an organism. • Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried. • Preserved remains form when an entire organism becomes encased in material such as ice. • Specific conditions are needed for fossilization. • • Radiometric dating provides an accurate way to estimate the age of fossils. • • – It compares the placement of fossils in layers of rock. – Scientists infer the order in which species existed. Radiometric dating uses decay of unstable isotopes. – Isotopes are atoms of an element that differ in their number of neutrons. – A half-life is the amount of time it takes for half of the isotope to decay. • The geologic time scale divides Earth’s history based on major past events. • Index fossils can provide the relative age of a rock layer. – existed only during specific spans of time • Index fossils include fusulinids and trilobites. • The geologic time scale organizes Earth’s history. • Eras last tens to hundreds of millions of years. – • consist of two or more periods -occurred in large geographic areas -three eras: Cenozoic, Mesozoic, Paleozoic Periods last tens of millions of years. – most commonly used units of time on time scale -associated with rock systems 8 • Epochs last several million years. • The origin of life on Earth remains a puzzle. Earth was very different billions of years ago. • There have been many hypotheses of Earth’s origins. • The most widely accepted hypothesis of Earth’s origins is the nebula hypothesis. • Several sets of hypotheses propose how life began on Earth. • There are two organic molecule hypotheses. – • 0meteorite hypothesis There are different hypotheses of early cell structure. – • Miller-Urey experiment iron-sulfide bubbles hypothesis -lipid membrane hypothesis A hypothesis proposes that RNA was the first genetic material. – Ribozymes are RNA molecules that catalyze their own replication. – DNA needs enzymes to replicate itself. • Single-celled organisms existed 3.8 billion years ago. Microbes have changed the physical and chemical composition of Earth. • The oldest known fossils are a group of marine cyanobacteria. – prokaryotic cells -added oxygen to atmosphere -deposited minerals • Fossil stromatolites provide evidence of early colonies of life. • Eukaryotic cells may have evolved through endosymbiosis. • Endosymbiosis is a relationship in which one organism lives within the body of another. • Mitochondria and chloroplasts may have developed through endosymbiosis. • The evolution of sexual reproduction led to increased diversity. • • Sexual reproduction may have led to the evolution of multicellular life. • Multicellular life evolved in distinct phases. • Multicellular organisms first appeared during the Paleozoic era. • The era began 544 million years ago and ended 248 million years ago. • The Cambrian explosion led to a huge diversity of animal species. • Life moved onto land in the middle of the Paleozoic era 9 • Reptiles radiated during the Mesozoic era. • The Mesozoic era is known as the Age of Reptiles. • It began 248 million years ago and ended 65 million years ago. • Dinosaurs, birds, flowering plants, and first mammals appeared. • Mammals radiated during the Cenozoic era. • The Cenozoic era began 65 million years ago and continues today. • Placental mammals and monotremes evolved and diversified. • Anatomically modern humans appeared late in the era. • Humans appeared late in Earth’s history. Humans share a common ancestor with other primates. • • • Primates evolved into prosimians and anthropoids. – Prosimians are the oldest living primates. – Anthropoids are humanlike primates. – They are subdivided into the New World monkeys, Old World monkeys, and hominoids. -they are mostly small and nocturnal Homonoids are divided into hominids, great apes, and lesser apes. • • Bipedal means walking on two legs. – Foraging -carrying infants and food • Walking upright has important adaptive advantages. • There are many fossils of extinct hominids. • Most hominids are either the genus Australopithecus or Homo. • Australopithecines were a successful genus. • The Homo genus first evolved 2.4 million years ago. • Modern humans arose about 200,000 years ago. • Homo sapiens fossils date to 200,000 years ago. • Human evolution is influenced by a tool-based culture. • There is a trend toward increased brain size in hominids. -using tools 10