Charles Darwin



Chapter 22 – Evolution and DarwinEvolution isn't linear. ?Myth 1: Organisms aren't striving to become anythingBecause people think evolution is linear, they say things like: If humans evolved into monkeys, why are there still monkeys?Myth 2: ?Scientists regularly debate whether evolution occurs.The only place debate occurs is in social settings, and is philosophical in nature. ?If any debate occurs among biologists, its often regarding specifics - such as timing, or what animal is related to what, or when did a creature evolve and what is its origins. ? ?As a THEORY, evolution is supported by a large body of evidence and is used to EXPLAIN new observations. ?Biologists would consider it a waste of time to debate this.Myth 3: A person cannot believe in God and in evolution.?There are many scientists who have religious beliefs. ? One does not necessarily preclude the other. ??To say that the two are incompatible is grossly unfair to both scientists and people of faith.?Myth 4 : ?evolution encourages the strong to destroy the weak. ?Remember, "strong" and "weak" are relative. ? Organisms do not have to be strong to survive.?There are many more myths and misunderstandings about evolution. ?We will hopefully tackle those as we progress through this unit.?Charles DarwinIn 1831, Charles Darwin, a 22-year-old naturalist, accepted a position aboard the ship HMS Beagle that began a voyage around the world; it provided Darwin with many observations.Prior to Charles DarwinPre-Darwinian world-view was determined by theological beliefs.1) The earth is young.2) Each species was specially created and did not change3) Variations are imperfections 4) Observations are to substantiate the prevailing worldview.5) Aristotle and Judeo-Christian viewpoints – “scala natuae” 6) Scientists were also usually theologiansLaying the groundwork for Darwin1707 – 1778 – Carolus Linneaus- taxonomy1726-1797 – James Hutton–gradualism, slow progress; earth is old.1797-1875 - Charles Lyell-uniformitarianism 1798 – Malthus – overreproduction1809 – Larmark – theory of evolutionLinneaus (1707-1778)Swedish taxonomist (taxonomy is the science of naming and classifying organisms.He developed a binomial system of nomenclature (two-part names for each species [e.g., Homo sapiens]). Like other taxonomists of his time, Linnaeus believed in the ideas ofa)?special creation—each species had an?“ideal”?structure and function; andb)fixity of species—each species had a place in the?scala naturae, a sequential ladder of life.Lamarck (1744-1829) first to state that descent with modification occurs Proposed inheritance of acquired characteristicshe believed that organisms become adapted to their environment.Lamarck mistakenly saw “a desire for perfection” as inherent in all living thingsShould be recognized for: claim of evolution, theorizing about great age of earthemphasis on adaptationHutton and LyellDarwin read their work and reached two important conclusions:The earth must be very old (much older than 6000 years)Many gradual changes over time will yield substantial changes.Charles Darwin 1809 - 1882Nature was primary interestMedical school – didn’t likeB.A. in theology from CambridgeHMS BeagleSailed in 1831Darwin was ship’s naturalistSailed for 5 years and surveyed coast of South America Voyage of the HMS BeaglePlants and animalsUniquely South AmericanMore closely related to each other than to organisms on other continentsFossils – uniquely SAGalapagos IslandOrganisms lived no where else on earthClosely resembled organisms from the mainlandDarwin’s FinchesFinches on the Galápagos Islands resembled a mainland finch but there were more types.Galápagos finch species varied by nesting site, beak size, and eating habits.One unusual finch used a twig or thorn to pry out insects, a job normally done by (missing) woodpeckersNatural SelectionDarwin decided that adaptations develop over time; he sought a mechanism by which adaptations might arise.Natural selection was proposed by both Alfred Russel Wallace and Darwin as a driving mechanism of evolution caused by environmental selection of organisms most fit to reproduce, resulting in adaptationDifferential success in reproductionOccurs through interaction between environment and variability in individualsProduct of natural selection is the adaptation of populations of organism to their environment4. Because the environment is always changing, there is no perfectly-adapted organism.5. There are three preconditions for natural selection.a. The members of a population have random but heritable variations.b. In a population, many more individuals are produced each generation than the environment can support.c. Some individuals have adaptive characteristics that enable them to survive and reproduce better.6. There are two consequences of natural selection.a. An increasing proportion of individuals in succeeding generations will have the adaptive characteristics.b. The result of natural selection is a population adapted to its local environment.7. Natural selection can only utilize variations that are randomly provided; therefore there is no directedness or anticipation of future needs.8. Extinction occurs when?previous adaptations are no?longer suitable to a changed anisms Struggle to ExistMalthus proposed that human populations outgrow food supply and death and famine were inevitable.Darwin applied this to all organisms; resources were not sufficient for all members to survive.Therefore, there is a constant struggle for existence; only certain members survive and reproduce.VariationsIn contrast to the previous worldview where imperfections were to be ignored, variations were essential in natural selection.2. Darwin suspected, but did not have today's evidence, that the occurrence of variation is completely random.3. New variations are as likely to be harmful as helpful.4. Variations that make adaptation possible are those that are passed on from generation to generation.5. Darwin could not state the cause of variations because genetics was not yet anisms differ in fitnessFITNESS is a measure of an organism’s reproductive successA polar bear can survive and reproduce in cold climates, it is not adapted to warmer climatesReproduction is important for evolution, only those who survive to reproduce pass on those advantageous genesArtificial Selection - Darwin used the power of artificial selection to reinforce natural selection Organisms Become Adapted1. An adaptation is a trait that helps an organism be more suited to its environment.?2. Unrelated organisms living in the same environment often display similar characteristics. (Convergent evolution)3. Because of differential reproduction, adaptive traits increase in each succeeding generation.Drawbacks of natural selectionCan only utilize variations that are randomly provided; there is no directedness or anticipation of future needsExtinctions occur when previous adaptations are no longer suitable to a changed environmentMacroevolution vs. MicroevolutionThese two ideas attempt to explain the difference between small changes (micro) versus large changes (macro). There is really no difference, other than macroevolution takes a very long time and results in profound changes in the speciesMicroevolution refers to minor changes that can occur within a species in a relatively short period of time, like a change in coloration within a fish populationSome subtleties: Population is the smallest unit that can evolve—individuals DO not evolve; Has to be a heritable characteristic and it’s situationalExamplesEvolution of insecticide resistant insects (page 437) and Evolution of drug resistant HIV – page 438Evidence of EvolutionFossil Record traces the history of life: Shows transitional fossils…Archaeopteryx and TiktaalikTransitional forms – Fossils that link older forms of an organism to the current formDarwin predicted it and we have found many.HomologyAnatomical homologiesVestigial organsEmbryologyical homologiesMolecular homologiesVestigial structures:Human appendix Pelvic bone in whales Eye sockets in blind salamander “It’s just a theory”2 problems with that statement:Darwin had two parts to his theoryOrganisms have and continue to evolveThey evolve by natural selection only part that is theoreticalTheory used in the scientific form not colloquial form. Theory is not a “guess.” It’s based on a lot of evidence. ................
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