CHAPTER 22 Descent with Modification A Darwinian View of Life The 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 another o mutation which creates a new allele that is favored How much time Several generations for the organism o for bacteria a day or two could be plenty o 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 or impressions of an organism or something related to an organism that lived in the past A succession of organisms is seen in the fossil record o The differences o New species between fossils and living species are great appeared and other became extinct However these results were not used to support evolution A French anatomist 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 of catastrophic 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 records were the result of uniformitarianism Uniformitarianism is the principle that profound change is the cumulative product of slow continuous processes This was the first indication that the changes seen on earth were usually slow If the changes were slow then the theological timeline of 6000 years must be in error Pre Darwinian Theory of Evolution Lamarck placed fossils in an evolutionary context Lamarck compared modern species to the fossil record and identified several lines 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 1 2 The mechanism of change involved two principles Use and disuse use it or lose it philosophy 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 fig 22 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 forms o 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 a common ancestor o Similar species have branched recently o Species with greater differences branched long ago o Most branches are dead ends Natural selection and adaptation Darwin s book focused on the role of natural selection in adaptation Darwin s observations and their inferences Observation 1 Populations have potential for exponential growth Observation 2 Population size is normally stable Inference 1 Survival is a struggle and only a fraction will survive Observation 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 from the 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 evolution Natural selection occurs from the interaction between the environment and the variability of the population o Variations o Environmental factors are defined criteria arise by chance mutations 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 classes Fish amphibians reptiles birds and mammals There 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 structures which evolve are known as analogous structures Analogous structures have similarity due to convergent evolution rather than the descent from a common ancestor with the same trait Ex insect wing and bird wing seal shape and penguin shape dolphin and shark
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