NOTES FOR BIOLOGY 1202DR. STEVEN POMARICO, INSTRUCTORCHAPTER 22Descent 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 modificationEvolution is change over time.What kind of change?A change in the frequency of the alleles of a population.-mutation which favors one allele over another.-mutation which creates a new allele that is favoredHow much time?Several generations for the organism-for bacteria => a day or two could be plenty-for humans => may be 200-300 years>>>>>>Darwin’s ideas were opposed by western philosophyThe most popular hypothesis for the origin of species was creationism---Creationism – states that al species were created exactly as they existed 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.1---Fossils – are preserved remnants or impressions of an organism or something related to anorganism that lived in the past. -A succession of organisms is seen in the fossil record.-The differences between fossils and living species are great.-New species appeared and other became extinctHowever, these results were not used to support evolution. A French anatomist (Cuvier) founded thescience of paleontology, the study of fossils in the late 1700's and early 1800's. Cuvier explained thelayers 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 theresult 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 theresult of uniformitarianism ---Uniformitarianism – is the principle that profound change is cumulative product of slow,continuous process 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 EvolutionLamarck placed fossils in an evolutionary context.Lamarck compared modern species to the fossil record and identified several lines of descent consistingof a succession of older fossils => younger fossils => modern species. In 1809 Lamarck’s comprehensivemodel 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. Thecomplexity of organisms increased in a “march toward perfection” and the most complex organisms wereat 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.2These ideas turned out to be wrong>>>>>>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)- observed that South American organisms differed from European forms- species of finches (see fig 22.6) in Galapagos Islands were unique but resembled species of South America.Darwin’s work was preceded in publication by the work of Wallace whose work was in completeagreement 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 1859Darwin used a tree as a metaphor for the history of life (see fig 22.7);-at each branch or fork the species have a common ancestor.-similar species have branched recently-species with greater differences branched long ago.-most branches are dead ends.>>>Natural selection and adaptationDarwin's book focused on the role of natural selection in adaptation. 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 phenotypesresulting from the interaction of organisms with their environment. 3“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.-Variations arise by chance (mutations).-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 themodern forms. >Comparative anatomy and taxonomyOrganisms of different types (birds versus mammals) evolve similar characteristics to handle a similarenvironmental 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 resultof having similar ecological roles and selection pressures.The similar structures which evolve are known as analogous structures--- Analogous structures – have similarity due to convergent evolution rather than from
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