LSU BIOL 1202 - CHAPTER 22: Descent with Modification: A Darwinian View of Life

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CHAPTER 22: Descent with Modification: A Darwinian View of LifeThe first “convincing” case of evolution was published by Charles Darwin in 1859.---Evolution is the transformation of the life forms on earth over time- Descent with modification- Evolution is change over time.- What kind of change?- A change in the frequency of the alleles of a population.o mutation which favors one allele over anothero mutation which creates a new allele that is favored- How much time?- Several generations for the organismo for bacteria  a day or two could be plentyo for humans  may be 200-300 years- if the phenotype changes, then this can be used as evidence of evolutionary change>>>>>>Darwin’s ideas were opposed by western philosophy- The most popular hypothesis for the origin of species was creationism---Creationism states that all species were created exactly as they exist today- May be strictly Biblical or may involve continual creation.>>>Fossils and a record of change.- The evidence of some of the organisms which have existed on earth is preserved as fossils.---Fossils are preserved remnants orimpressions of an organism orsomething related to an organismthat lived in the past- A succession of organisms isseen in the fossil record.o The differencesbetween fossils andliving species are great.o New species appearedand other becameextinctHowever, these results were notused to support evolution. A Frenchanatomist (Cuvier) founded the science of paleontology, the study of fossils in the late 1700's and early 1800's. Cuvier explained the layers of different species were caused by separate catastrophic events.This philosophy is known as catastrophism---Catastrophism is a theory which states that the major changes in the earth’s crust are the result ofcatastrophic events rather than gradual process of change>>>>>>Geological gradualism: the predecessor of evolution.- In the late 1700's a geologist (Hutton) proposed that the large changes seen in the fossil recordswere the result of uniformitarianism ---Uniformitarianism is the principle that profound change is the cumulative product of slow,continuous processes- This was the first indicationthat the changes seen onearth were usually slow.- If the changes were slow, thenthe theological timeline of6000 years must be in error.>>>>>> Pre-Darwinian Theory ofEvolutionLamarck placed fossils in anevolutionary context.Lamarck compared modern species tothe fossil record and identified severallines of descent consisting of a succession of older fossils  younger fossils  modern species. In 1809 Lamarck’s comprehensive model was published- Lamarck envisioned many “ladders” of evolution which organisms could “climb.”- The least complex organisms at the bottom of the ladders were spontaneously generated. The complexity of organisms increased in a “march toward perfection” and the most complex organisms were at the top of the ladder.- The mechanism of change involved two principles:1. Use and disuse - use it, or lose it philosophy2. Acquired traits can be passed along to the next generation.o These ideas turned out to be wrong (giraffe with longer necks, driven by “inner need”>>>>>>Darwin and the voyage of the HMS Beagle (see fig22.5)Charles Darwin (1809-1882) was born the year Lamarck published his work on evolution.- He sailed on the voyage of the Beagle (1831)o observed that South American organisms differed from European formso Species of finches (see fig 22.6) in Galapagos Islands were unique but resembled species of South America.o Noticed different beaks- Darwin’s work was preceded in publication by the work of Wallace whose work was in complete agreement with the hypotheses championed by Darwin.- The work by Wallace prompted a hesitant Darwin to complete the work he began years earlier. - Darwin’s observations lead to The Origin of Species published in 1859- Darwin used a tree as a metaphor for the history of life(see fig 22.7) o At each branch or fork the species have acommon ancestoro Similar species have branched recentlyo Species with greater differences branched longagoo Most branches are dead ends>>>Natural selection and adaptationDarwin's book focused on the role of natural selection inadaptation. Darwin’s observations and their inferences:Observation 1. Populations have potential for exponential growthObservation 2. Population size is normally stableInference 1. Survival is a struggle, and only a fraction will surviveObservation 3. Traits are variable among individuals of a population.Inference 2. Survival is not usually random, but is largely dependent upon heritable traits.Survival of the fittest.Observation 4. Most of those variable traits can be inherited.Inference 3. Unequal survival of individuals will lead to gradual change in population.Natural selection is differential success in reproduction. ---Natural selection is the differential success in the reproduction of different phenotypes resulting fromthe interaction of organisms with their environment.“Nature” picks the phenotypes that will survive.The result of natural selection is the adaptation of organisms to their environment.- This adaption is evolutionNatural selection occurs from the interaction between the environment and the variability of thepopulation.o Variations arise by chance (mutations).o Environmental factors are defined criteria Natural selection is insured by an excess of offspring and variation in the population.Small changes accumulated each generation can result in major changes over evolutionary time.>>>>>>The evidence for evolution >>>The fossil record shows a sequential appearance of organisms Prokaryotes are the oldest forms of life  There is a chronological appearance of vertebrate classesFishamphibiansreptilesbirds and mammalsThere are progressive series of fossils leading from primitive form through intermediate forms to the modern forms. >Comparative anatomy and taxonomy- Organisms of different types (birds versus mammals) evolve similar characteristics to handle a similar environmental challenge.- This process of making similar structures is convergent evolution (see fig 22.18)--- Convergent evolution is the independent development of similarity between species as a result of their having similar ecological roles and selection pressures (sugar glider in Australia vs. flying squirrel in North America)The similar


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LSU BIOL 1202 - CHAPTER 22: Descent with Modification: A Darwinian View of Life

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