Chem Outline Chap 1-4
Chem Outline Chap 1-4 CHEM0110
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Date Created: 02/01/15
Chapter 25 Evolution by Natural Selection The Evolution of Evolutionary Though A Plato and Typological Thinking 1 Plato claimed that every organism was an example of a perfect essence or type created by God and that these types were unchanging 2 Typological thinking is based on the idea that species are unchanging types and that variations within species are unimportant or even misleading B Aristotle and the Great Chain of Being 1 3 Aristotle ordered the types of organisms known at the time into a linear scheme called the great chain of being or scale of nature Proposed that species were organized into a sequence based on increased size and complexity with humans at the top Also claimed that characteristics of species were xed and don t change throughout time C Lamarck and the Idea of Evolution as Change through Time 1 3 Lamarck proposed a formal theory of evolution that species are not static but change through time a However the pattern component was initially based on the great chain of being Claimed that simple organisms originate at the base of the chain by spontaneous generation and then evolve by moving up the chain over time a Progressive in the sense of always producing larger and more complex species Also contended that species change through time via the inheritance of acquired characteristics D Darwin and Wallace and Evolution by Natural Selection 1 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 a A population consists of individuals of the same species that are living in the same area at the same time Darwin claimed that instead of being unimportant or an illusion variation among individuals in a population was the key to understanding the nature of species This is population thinking The theory of evolution by natural selection was revolutionary because a It overturned the idea that species are static and unchanging b It replaced typological thinking with population thinking c It was scienti c and proposed a mechanism that could account for change through time and made predictions that could be tested through observation and experimentation The Pattern of Evolution Have Species Changed Are They Related A Darwin described evolution as descent with modi cation which meant that species that lived in the past are the ancestors of the species existing today and that species change through time B The pattern component of the theory of evolution by natural selection makes two predictions about the nature of species 1 Species change through time 2 Species are related by common ancestry C Evidence for Change through Time 1 A fossil is any trace of an organism that lived in the past a The fossil record consists of all the fossils that have been found on Earth and described in the scienti c Hterature b Extant species are species still living today 2 The Vastness of Geologic Time a Sedimentary rocks form from sand or mud or other materials deposited at locations such as beaches or river mouths They are known to form in layers i Scientists use this information to place fossils in a chronological order ii They can create a geologic time scale a sequence of named intervals called eons eras and periods that represented that major events in earth s history b The geologic record indicated that the Earth was much older than 6000 years c Earth is about 46 billion years old and the earliest signs of life appear in rocks that formed 3438 billion years ago 3 Extinction Changes the species Present Over Time a Extinct species are those that no longer exist b Darwin interpreted extinct forms as evidence that species are not static because if species have gone extinct then the array of species living on earth has changed through time i Over 99 of all the species that have ever lived are now extinct 4 Transitional Features Link Older and Younger Species a Darwin said that extinct forms and living forms were related they represented ancestors and descendants b A transitional feature is a trait in a fossil species that is intermediate between those of ancestral and derived species i If the traits observed in more recent species evolved from traits in more ancient species then transition forms are expected to occur in the appropriate time sequence 5 Vestigial Traits are Evidence of Change Through Time a 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 6 Current Examples of Change through Time a Species are dynamic not static D Evidence of Descent from a Common Ancestor 1 Similar Species Are Found in the Same Geographic Area a A phylogenetic tree is a branching diagram that describes the ancestordescendant relationships among species or other taxa 2 Similar Species Share Homologies a C Homology is a similarity that exists in species because they inherited the trait from a common ancestor i Genetic homology occurs in DNA nucleotide sequences RNA nucleotide sequences or amino acid sequences ii Developmental homology is recognized in embryos iii Structural homology is a similarity in adult morphology or form Genetic homologies cause the developmental homologies observed in embryos which then lead to the structural homologies recognized in adults The theory of evolution by natural selection predicts that homologies will occur If species were created independently of one another these types of similarities wouldn t happen 3 Current Examples of Descent from a Common Ancestor a The contemporary examples of new species being formed are powerful evidence that species living today are the descendants of species that lived in the past E Evolution s quotInternal Consistencyquot The Importance of Independent Data Sets 1 2 3 The most powerful evidence for evolution by natural selection is internal consistency the observation that data from independent sources agree in supporting predictions made by a theory Data from many different sources are much more consistent with evolution than with special creation Descent with modi cation is a successful and powerful scienti c theory because it explains observations Ill The Process of Evolution How Does Natural Selection Work A Darwin s Inspiration 1 Darwin crossbred pigeons and observed how characteristics were passed on to offspring He could choose certain individuals with desirable traits to reproduce manipulating the population with arti cial selection B Darwin s Four Postulates 1 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 they are passed on to offspring In each generation many more offspring are produced than can possibly survive Thus only some survive long enough to produce offspring and 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 Individuals with certain heritable traits are more likely to survive and reproduce a Natural selection occurs when individuals with certain characteristics produce more offspring than do individuals without those characteristics b Because the selected traits are passed on to offspring the frequency of the selected traits increases from one generation to the next The outcome of evolution by natural selection is a change in allele frequencies in a population over time Evolution by natural selection occurs when 1 heritable variation leads to 2 differential reproductive success C The Biological De nitions of Fitness Adaptation and Selection 1 Biological tness is the ability of an individual to produce surviving fertile offspring relative to that ability in other individuals in the population a Fitness is a measurable quantity An adaptation is a heritable trait that increases the tness of an individual in a particular environment relative to individuals lacking the trait a Adaptations increase tness Selection refers to a passive process differential reproduction as a result of heritable variation not a purposeful choice IV Evolution in Action Recent Research on Natural Selection A The theory of evolution by natural selection is testable B Case Study 1 How Did Mycobacterium tuberculosis Become Resistant to Antibiotics 1 JUN Mycobacterium tuberculosis is the bacterium that causes tuberculosis a It usually infects the lungs and causes fever coughing sweats weight loss and often death In the late 19805 rates of TB surged in many contries A Patient History a Drugresistent Mycobacterium tuberculosis cells killed the patient b Because of a point mutation in a gene called rpoB A Mutation in a Bacterial Gene Confers Resistance a The rpoB gene codes for a component of RNA polymerase The point mutation changed a cytosine to a thymine forming a new allele b Rifampin the antibiotic that was being used to treat the patient works by binding to the RNA polymerase of Mycobacterium tuberculosis and interfering with transcription Testing Darwin s Postulates a Did variation exist in the population Yes Due to mutation both resistant and nonresistant strains of TB were present before administration of the drug b Was this variation heritable Yes The researchers showed that the variation in the phenotypes of the two strains was due to variation in their genotypes c Was there variation in the reproductive success Yes Only a tiny fraction of cells in the patient survived the rst round of antibiotics long enough to reproduce 15 Did selection occur Yes When rifampin was present certain cells those with the drugresistant allele had higher reproductive success than cells with the normal allele Natural selection acts on individuals because individuals experience differential reproductive success But only populations evolve Allele frequencies change in populations not in individuals 6 Drug Resistance A Widespread Problem a Evolution has occurred because individuals with the heritable ability to resist some chemical compound were present in the original population C Case Study 2 Why are Beak SizeShape and Body Size Changing in Galapagos Finches 1 Beak size and shape and body size vary among individuals and beak morphology and body size are heritable 2 Selection during Drought Conditions a b C In the annual wet season of 1977 the environment received 24mm of rain instead of the normal 130mm Few plants were able to produce seeds and 84 of the nch population died The die off was a natural experiment which allows researchers to compare treatment groups created by an unplanned change in conditions Survivors tended to have deeper beaks that the birds that died i Because most seed sources were inside tough fruits that needed cracked In only one generation natural selection led to a measurable change in the characteristics of the population Alleles that had led to the development of deep beaks had increased in frequency 3 Continued Changes in the Environment Continued Selection a b In 1983 the environment changed again and small individuals with small pointed beaks had higher tness than those with large deep beaks Alleles associated with small pointed beaks increased in frequency 4 Which genes are Under Selection a Characteristics like bodybeak size and body shape are polygenic meaning that many genes in uence the trait Common Misconceptions about Natural Selection and Adaptation A Evolution by natural selection is a simple process B Selection acts on Individuals but Evolution Occurs in Populations 1 During natural selection individuals do not change populations do 2 Natural Selection is Not quotLamarckianquot Inheritance a C Lamarck proposed that 1 individuals change in response to challenges posed by the environment and 2 the changed traits are then passed on to offspring In contrast Darwin realized that individuals don t change when they are selected but simply produce more or less offspring than others Natural selection just sorts existing variants it doesn t change them 3 Acclimatization is NotAdaptation a Acclimatization is a change in an individual s phenotype that occurs in response to a change in natural environmental conditions Phenotypic changes due to acclimatization are not passed on to offspring because no alleles have changed C Evolution is Not Goal Directed 1 Mutations do not occur to solve problems they simply happen 2 Adaptations do not occur because organisms want or need them 3 Evolution isn t Progressive a Complex traits are routinely lost or simpli ed over time as a result of evolution by natural selection 4 There Is No Such Thing as a Higher or Lower Organism D Organisms Do Not Act for the Good of the Species 1 Individuals with selfsacri cing alleles die and do not produce offspring But individuals with sel sh cheater alleles survive and produce offspring 2 Sel sh alleles increase in frequency E There Are Constraints on Natural Selection 1 Nonadaptive Traits a Vestigial traits do not increase tness b Some adult traits exist as holdovers from structures that appear early in development 2 Genetic Constraints a Genetic correlations occur because of pleiotropy in which a single allele affects multiple traits b Lack of genetic variation 3 Fitness Tradeoffs 1 In nature selection occurs in the context of tness tradeoffs a compromise between traits in terms of how they perform in the environment 2 Because selection acts on so many traits at once every adaptation is a compromise 4 Historical Constraints a All traits have evolved from previously existing traits
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