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This 7 page Study Guide was uploaded by Saida Muktar on Sunday February 14, 2016. The Study Guide belongs to Bii at University of Maryland - Baltimore County taught by Dr. Omland in Winter 2016. Since its upload, it has received 59 views.
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Date Created: 02/14/16
25.1 THE EVOLUTION OF EVOLUTIONARY THOUGHT A scientific revolution overturns an existing idea about how nature works and replaces it with another idea. Darwin and Wallace overturned that species were supernaturally, not naturally, created. Palto and Typological Thinking. o Typological thinking is based on the idea that species are unchanging types and that variations within species are unimportant or even misleading. Aristotle and the Great Chain of Being o Aristotle's central claims were 1. Species are fixed types 2. Some species are higher - in the sense of being more complex or "better" - than others. Lamarck and the Idea of Evolution as Change through Time o Lamarck proposed a formal theory of EVOLUTION - that species are not static but change through time. o Lamarck claimed that simple organisms originate at the base of the chain by spontaneous generation and then evolve by moving up the chain over time. o Lamarckain evolution s progressive in the sense of always producing larger and more complex, or "better," species. 1. He contended that species change though time through the inheritance of acquired characters. An individual develops in response to challenges posed by the environment, and it passes on these phenotypic changes to offspring. Giraffes develop long necks as they stretch to reach leaves high in treetops and they then produce offspring with elongated necks. Darwin and Wallace and Evolution by Natural Selection o Darwin and Wallace emphasized that the process responsible for change through time - evolution - occurs because traits vary among the individuals in a population, and because individuals with certain traits leave more offspring than others do. o A POPULATION consists of individuals of the same species that are living in the same area at the same time. o Darwin claimed that variation among individuals in a population was the key to undertanding the nature of species. This was viewed as POPULATION THINKING. o The theory of evolution by natural selection was revolutionary because 1. It overturned the idea that species are unchanging 2. It replaced typological thinking with population thinking 3. It was scientific. It proposed a mechanism that could account for change through time and made predictions that could be tested through observation and experimentation. 25.2 THE PATTERN OF ECOLUTION: HAVE SPECIES CHANGED, AND ARE THEY RELATED? DESCENT W/ MODIFIATION - species that lived in the past are the ancestors of the species existing today, and that species change through time. The pattern component of the theory of evolution by natural selecton makes two prediction about the nature of species : 1 Species change though time 2 Species are related by common ancestry Evidence for Change Through Time o A FOSSIL is any trace of an organism that lived in the past o The FOSSIL RECORD consists of all the fossils that have been found on Earth and describe in the scientific literature. o Initially, fossils were organized according to their relative ages based on a series of principles derived from observations about rock formation. Scientists observed similarities in rocks and fossils at different sites, they began to create a GEOLOGIC TIME SCALE: a sequence of named intervals called enos, eras and periods that represented the major events in Earth history. The geologic record indicated that the Earth was much older than 6000 years o Radiometric dating is based on three information: Observed decay rates of parent to daughter atoms The ration of parent to daughter atoms present in newly formed rocks The ration of parent to daughter atoms present in a particular rock sample o Earth is about 4.6 billion years old, and the earliest signs of life appear in rocks that formed 3.4-3.8 billion years ago. o Over 99% of all the species that have ever lived are now extinct. o "Law of succession" - Extinct species in the fossil record was succeeded, in the same region, by similar species. o A TRANSITIONAL FEATURE is a trait in a fossil species that is intermediate b/n those of ancestral and derived (younger) species. If the traits observed in more recent species evolved from traits in more ancient species, then transitional forms are expected to occur in the appropriate time sequence. o A VESTIGIAL TRAIT is a reduced or incompletely developed structure that has no function, or reduced function, but is clearly similar to functioning organs or structures in closely related species. Vestigial traits are evidence that the characteristics of species have changed over time. Evidence of Descent from a Common Ancestor o Similar Species share Homologies HOMOLOGY is a similarity that exists in species b/c they inherited the trait from a common ancestor. Human hair and dog fur are homologous b/c they share a common ancestor. Homology can be recognized and studied at three levels: GENETIC HOMOLOGY occurs in DNA nucleotide sequences, RNA nucleotide sequences, or amino acid sequences. For example the eyeless gene in fruit flies and the Aniridia gene in humans are so similar that their protein products are 90% similar in amino acid sequence. DEVELOPMENTAL HOMOLOGY is recognized in embryos. For example, early chick, human and cat embryos have tails and structures called gill pouches and later , gill pouches are lost in all three and tails are lost in humans. STRUCTURAL HOMOLOGY is a similarity in adult morphology, or form. The three levels of homology interact. Genetic homologies cause the developmental homologies observed in embryos, which then lead to the structural homologies recognized in adults. The most fundamental of all homologies is the genetic code. With a few minor exceptions, all organisms use the same rules for transferring the information coded in DNA into proteins. The theory of evolution by natural selection predicts that homologies will occur. If species were created independently of one another, as special creation claims, these types of similarities would not occur. Evolution's "Internal Consistency" - The Importance of Independent Data Sets o Perhaps the most powerful evidence for any scientific theory, including evolution by natural selection is what scientists call internal consistency. This observation that data from the independent sources agree in supporting predictions made by a theory. 25.3 THE PROCESS OF EVOLUTION: HOW DOES NATURAL SELECTION WORK? Darwin's Inspiration o Darwin used pigeon breeding as a model system that would be easier to study and manipulate than populations in the wild. Darwin crossbred pigeons and observed how characteristics were passed on to offspring. He could choose certain individuals with desirable traits to reproduce, thus manipulating the composition of the population by a process called ARTIFICIAL SELECTION. o An Essay on the Principle of Population Since many more individuals were born than can survive, a "struggle for existence" occurs as people compete for food and places to live. o Darwin combined his observations of artificial selection with the notion of "struggle for existence" in natural populations, which he knew contained variation. This arose his concept of natural selection. Darwin's Four Postulates o Darwin broke the process of evolution by natural selection into four simple postulates that form a logical sequence: The individual organisms that make up a population vary in the traits they possess, such as their size and shape Some of the trait differences are heritable, meaning that they are passed on to offspring In each generation, many more offspring are produced than can possible survive. Thus, only some individuals in the population survive long enough to produce offspring, and among the individuals that produce offspring, some will produce more than others. The subset of individuals that survive best and produce the most offspring is not a random sample of the population. Instead, individuals with certain heritable traits are more likely to survive and reproduce. NATURAL SELECTION occurs when individuals with certain characteristics produce more offspring than do individuals without those characteristics. o The outcome of evolution by natural selection is a change in allele frequencies in a population over time. o Evolution by natural selection occurs when heritable variation leads to differential reproductive success. The Biological Definitions of Fitness, Adaptation, and Selection o Darwin referred to successful individuals as "more fit" than other individuals. o FITNESS is the ability of an individual to produce surviving, fertile offspring relative to that ability in other individuals in the population. o ADAPTATION is a heritable trait that increases the fitness of an individual in a particular environment relative to individuals lacking the trait. o Adaptations increase fitness - the ability to produce viable, fertile offspring. 25.4 EVOLUTION IN ACTION: RECENT RESEARCH ON NATURAL SELECTION The theory of evolution by natural selection is testable. Read case studies 25.2 COMMON MISCONCEPTIONS ABOUT NATURAL SELECTION AND ADAPTATION Selection Acts on Individuals, but Evolutionary Change Occurs in Populations o Perhaps the most important point to clarify about natural selection is that during the process, individuals do not change - only the population does. o Natural Selection is Not "Lamarckian" Inheritance There is a sharp contrast between evolution by natural selection and evolution by the inheritance of acquired characters. Lamarck proposed that: 1. Individuals change in response to challenges posed by the environment 2. The changed traits are then passed on to offspring. He claimed that evolutionary changes occur in individuals Darwin realized that individuals do not change when they are selected. 1. Instead, they simple produce more or less offspring than other individuals do. 2. When this happens, alleles found in the selected individuals become more or less frequent in the population. There is no mechanism that makes it possible for natural selection to change the nature of an allele inside an individual. An individual's heritable characteristics don't change when natural selection occurs. Natural selection just sorts existing variants - it doesn't change them. Acclimatization is Not Adaptation o The issue of change in individuals is tricky because individuals often do not change in response to changes in environment. o ACCIMATIZATION is a change in an individual's phenotype that occurs in response to a change in natural environmental conditions. o Phenotypic changes due to acclimatization are not passed on to offspring, because no alleles have changed. o Acclimatization does not cause evolution. Evolution is Not Goal Directed o Mutations do not occur to solve problems. Mutations just happen. o Every mutation is equally likely to occur in every environment. There is no mechanism that enables the environment to direct which mistakes DNA polymerase makes when copying genes. Adaptations do not occur because organisms want or need them. o Evolution is not progressive Complex traits are routinely lost or simplified over time as a result of evolution by natural selection. o There is no such thing as a higher or lower organism A human is no higher than its tapeworm parasite; each is well adapted to its environment. "Evolutionary change occurs in organisms" - False Natural selection just sorts existing variants in organisms; it doesn't change them Evolutionary change occurs only in populations Acclimatization is not adaptation "Adaptations occur because organisms want or need them" - False Mutation, the source of new alleles, occurs by chance Evolution is not goal directed or progressive There is no such thing as a higher or lower organism "Organisms sacrifice themselves for the good of the species" Individuals with alleles that cause self-sacrificing behavior die and do not produce offspring, so these alleles are eliminated from the population "Evolution perfects organisms" Some traits are nonadaptive Some traits cannot be optimized due to fitness trade-offs Some traits are limited by genetic or historical constraints There Are Constraints an Natural Selection o Nonadaptive Traits Vestigial traits such as the human coccyx (tailbone) and goose bumps do not increase the fitness of individuals with those traits. The structures are not adaptive. They exist because they were present in the ancestral population. o Genetic Constraints Genetic correlations occur because of pleiotropy in which a single allele affects multiple traits o Fitness Trade-offs In nature, selection occurs in the context of fitness trade- offs. A FITNESS TRADE-OFF is a compromise between traits, in terms of how those traits perform in the environment. Because selection acts on many traits at once, every adaptation is a compromise o Historical Constraints
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