Chapter 22Wednesday, January 27, 20161:55 PM Chapter 22: Descent with Modification What is Evolution?-Misconceptions: oSpecies are always evolving into higher/better beingsoEvolution creates new forms of life by dramatic mutationsoAn organism can evolve during its lifetimeoAn organism can influence the evolution of its own structures in response to its environmentoEvolution is a completely random process-Evolution: o= the change in organisms throughout earth's historyo"descent with modification" (Charles Darwin) Views of Life Before Darwin-Antiquity through 1600'sAristotle and fixed ideal species-Scala naturae (ladder of nature)-Age of Reason (1700's - 1800's)Linnaeus's nested classification system Cuvier's interpretation of fossils-A record of change over time (different layers)-Sedimentary rock strata reveal relative agesoLower levels were older vs. higher levels-Catastrophic events caused extinctions followed by recolonizationHutton and gradual processes-Gradualism oSlow, continuous processes in the past, produced big geological featuresLyell and uniformitarianism-Father of geology-Geologic features were made by same processes (both catastrophic and gradual) at the same rate as today-Thus, earth is extremely old-Lyell's "Principles of Geology" was read by DarwinErasmus Darwin's "natural philosophy" on evolution-Ideas that "minute forms" "improved" over time, gaining complexityLamarck tied evolution to adaptation-Extinct species were replaced by descendants with new features (adaptations) that helped them survive in environment-First to propose a mechanism for evolutionoFeatures are modified by "use and disuse"-Lamarckism (wrong)oThese changes are passed on to offspring, "inheritance of acquired characteristics" Charles Darwin and His Theory-Darwin's VoyageoNaturalist on HMS Beagle 1831-1836oGoal mostly to South America, including Galapagos IslandsoCollected plants, wildlife, fossilsoObserved species' geographic locales and adaptationsoStudied local geology-Saw evidence for Lyell's uniformitarianism, that earth was possibly millions y/o-Darwin's Life WorkoMarriage and family allowed time for researchoEvolution theory developed-Essay written in 1844 but not published-In 1858, Alfred Wallace wrote a letter to Darwin with the same ideas-In 1858, both works presented publiclyoIn 1859, Darwin's book "Origin of Species"oResearched and wrote until death at 73-Darwin's TheoryoPart 1) All present life is related through "descent with modification" from a common ancestor in the past-"Evolution" not a completely "new" idea-Extinction is commonoPart 2) Natural selection is the mechanism for evolution-Obs. 1: In most species, there is some variation among individuals that is heritable-[22.10] Lady bug variation easy to see (enhancing over time)-Darwin saw that artificial selection (breeding) could enhance small heritable variations-[22.9] Wild cabbage variation is more subtle, but through artificial selection, variation is made more obvious-Obs. 2: All species produce more offspring than the environment can support-Many offspring will die before maturity-[22.11] An abundance of fish/tadpole eggs are laid, however notall will survive-Malthus observed this in humans:-Human population growth potential is exponential-But growth is restrained by limited resources (leading to increase) competition-Poorest and weakest suffered the most-Inference 1: Individuals with traits that help them survive and reproduce in their environment leave more offspring than other individuals (unequal reproductive success)-[1.18] The bug that is more likely to be eaten by birds will have no offspring; the darker bugs less eaten are more likely to leave offspring-Inference 2: those favorable, heritable traits (adaptations) accumulate over vast time, matching species to environment and ultimately leading to new species-[1.18] Population with varied inherited traits, with the elimination of individuals with certain traits. There will be a reproduction of the survivors. Increasing frequency of traits that enhance survival and reproductive success (adaptations)-Different varieties in artificial selection-Different species in natural selection due to different environments and nature's choice-[22.12] Ancestral praying mantis - natural selection leads to different adaptations in different environments-NOT in Darwin's TheoryoOrigin of lifeoHow variation arisesoHow inheritance worksoWhy variation still existso"Sudden" changes in fossil recordoSource of totally "new" characters Evidence in Support of Darwin's Theory-Direct ObservationoEx. Bugs adapt to new food sourceo[22.13] Soapberry bug on native balloon vine fruit-Native balloon vine fruit - most efficient if beak length matches the depth of fruit-Nonnative raintree fruit - flatter pods with less depthoEx. Antibiotic-resistance in bacteria-Surviving S. aureus gave rise to MRSA-Fossil RecordoFossil evidence of many extinct speciesoFossil evidence of transition of form-[22.20] Ex. Whales - pelvis and hind limbs in recent whale ancestor>fully aquatic>predominantly aquatic>terrestrial-Homologyo= similarity in form as a result of common ancestry-Homologous structures-= structure derived from a common ancestor (but may be modified for different functions)-[22.15] Ex. Mammal forelimbs are homologous-We used shared homologies to build evolutionary trees-Vestigial structures-= remnants of ancestral (homologous) structures with no present adaptive function-Ex. Blind cave salamanders have eyes, but must have descended from salamanders with eyes - inferred that descended from a species that could see-Developmental homologies-[22.16] Ex. Vertebrate embryos-Molecular and cellular homologies-Genetic code is universal-Similarity of cells, proteins, DNA corresponds to degree of relatedness-Ex. Species with the more similar proteins, DNA, cellular components are more closely related to each other-Convergenceo= unrelated species have similar adaptations (analogous structures) under similar environmental conditions-Why? Convergent evolution-Ex. Torpedo shape for swimming-Ex. Cacti thick stems and thorns in deserts-Ex. Tree-gliding mammals-Flying squirrel - relative of squirrel-Sugar glider - relative of opossum-Biogeographyo= distribution of species-Corresponds to geographic history-[25.16] Ex. Isolated Australian marsupials - koalas, possum, wombat, kangaroo-Ex. Unique (endemic) species on islands are similar to nearest mainland species Just a Theory?-Scientific Theoryo= a broad,