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Ch. 16 Darwin’s Theory of Evolution. 16.1, Darwin’s voyage of discovery. Darwin’s epic journey evolution: process of change over time Charles Darwin grew up @ time when scientific view of nature was shifting dramatically - PowerPoint PPT Presentation
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CH. 16DARWIN’S THEORY
OF EVOLUTION
Darwin’s epic journeyevolution: process of change over timeCharles Darwin grew up @ time when
scientific view of nature was shifting dramatically geologists 1st suggested Earth was ancient & had changed over time, & biologists suggested life had too
Darwin developed theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors
16.1, Darwin’s voyage of discovery
journey, contDarwin was invited to sail on HMS
Beagle’s 5-yr voyage mapping coastline of South America as ship’s naturalistcollected specimens of plants & animals on voyage
observations aboard HMS Beagle 3 major observations
different, yet ecologically similar, species inhabited separated, but ecologically similar, habitats around globeex.: rheas, emus, & ostriches are large, flightless birds living in similar grasslands on different continents
16.1, Darwin’s voyage, cont
observations, cont3 major observations, cont
different, related, species often occupied different habitats w/in local areaex.: tortoises on Galápagos Islands have different shells, depending on habitat type of their home island
some fossils of extinct species were similar to living speciesfossils: preserved remains or traces of ancient organisms
ex.: glyptodont – extinct, giant, armored animal similar to armadillo
16.1, Darwin’s voyage, cont
16.2, ideas that shaped Darwin’s thinking•ancient, changing Earth• based on work of other researchers & evidence they uncovered, Geologists James Hutton & Charles Lyell concluded Earth is extremely old & processes that changed Earth’s past also operate now•Hutton & geological change•connections between geological processes & geological features (layered rock built by sediment, mountains pushed up & then worn down, etc.)•slow processes, so our planet must be much older than few thousand years•called this deep time – our planet’s history stretches back so long that it’s difficult to imagine
16.2, ideas, cont•ancient, cont•Lyell’s Principles of Geology•presented uniformitarianism – idea that geological processes we see today must be same ones that shaped Earth millions of years ago (volcanism, erosion by rivers, etc.)
•both Hutton’s & Lyell’s theories depend on ancient Earth (> few 1000 yrs. of recorded history)•Darwin saw evidence that Lyell was correct•witnessed earthquake that lifted shoreline > 3 m up, w/ sea animals clinging to it• later, observed fossils of marine animals in mountains 1000s of feet above sea level
16.2, ideas, cont•Lamarck’s evolutionary hypotheses• in 1809, Jean-Baptiste Lamarck proposed that organisms could change during their lifetimes by selectively using or not using various parts of their bodies•thought all organisms w/ inborn urge to become more complex & perfect•acquired characteristics: traits altered by individual organism during its life
•Lamarck also thought organisms could pass on alterations made during its lifetime to its offspring (inheritance of acquired characteristics)
16.2, ideas, cont•Lamarck, cont•evaluating Lamarck’s ideas•no inborn drive to become more perfect•evolution does not mean that species becomes “better” somehow•traits acquired by individuals during their lifetime cannot be passed on to offspring
• important because Lamarck was one of 1st naturalists to suggest that species are not fixed•tried to explain evolution scientifically using natural processes•recognized link between organism’s environment & its body structures
16.2, ideas, cont•population growth•Thomas Malthus & populations• in 1798, Malthus noted that humans were being born faster than people were dying, causing overcrowding•suggested that forces against population growth include war, famine, & disease•reasoned that if human population grew unchecked, there wouldn’t be enough living space & food for everyone
•Darwin realized that Malthus’s reasoning applied to other organisms
16.2, ideas, cont•artificial selection•plant & animal breeders knew individual organisms vary, & that some of this variation could be passed from parents to offspring & used to improve crops/livestock•artificial selection: process in which nature provides variations, & humans select those they find useful•Darwin tested artificial selection by raising & breeding plants & fancy pigeon varieties•Darwin had no idea how heredity worked or what caused variation, but he knew that variation occurs in wild species too
16.3, DARWIN PRESENTS HIS CASE evolution by natural selection
natural selection occurs in any situation in which more individuals are born than can survive, there is natural heritable variation, & there is variable fitness among individuals
struggle for existence after reading Malthus, Darwin realized
that if more individuals are produced than can survive, they must compete for food, living space, etc.
variation & adaptation Darwin knew that individuals have
natural variations among their heritable traitshe hypothesized that some variants
are better suited to life in their environment than others
16.3, CASE, CONT natural selection, cont
survival of the fittest fitness: how well organism can survive & reproduce in its environmentindividuals w/ adaptations that are well-suited to their environment can survive & reproduce, so are said to have high fitness
individuals w/ characteristics that are not well-suited to their environment either die w/o reproducing or leave few offspring, so are said to have low fitness
survival of the fittest: difference in rates of survival & reproduction
16.3, CASE, CONT natural selection, cont
natural selection: process by which organisms w/ variations most suited to their local environment survive & leave more offspring similar to artificial selection, but
environment determines fitness, instead of breeder
generation to generation, populations continue to change as they become better adapted, or environment changes
acts only on inherited traits because those are only characteristics parents can pass on to offspring
adaptations don’t have to be perfect — just good enough to let organism pass its genes to next generation
16.3, CASE, CONT common descent
according to principle of common descent, all species — living & extinct — are descended from ancient common ancestors
natural selection depends on ability of organisms to reproduce & leave descendants, so organisms today descended from parents who survived & reproduced
Darwin proposed that, over many generations, adaptation could cause successful species to evolve into new species descent w/ modification: proposal that living
species are descended, w/ some changes, from common ancestors
for evidence of descent w/ modification, Darwin pointed @ fossil record
single “tree of life” links all living things
16.4, EVIDENCE OF EVOLUTION biogeography
patterns in distribution of living & fossil species tell us how modern organisms evolved from their ancestors
biogeography: study of where organisms live now & where they & their ancestors lived in past
2 biogeographical patterns significant to Darwin’s theoryclosely related species differentiate in slightly different climatesex.: biogeography of Galápagos species suggested that island populations (tortoises, finches, etc.) evolved from mainland species
over time, natural selection on islands produced variations
16.4, EVIDENCE, CONT biogeography, cont
2 patterns, cont very distantly related species develop similarities in similar environmentsground-dwelling birds (rheas, ostriches, and emus) inhabit similar grasslands in Europe, Australia, and Africa
differences in body structures provide evidence that they evolved from different ancestors
similarities among provide evidence that similar selection pressures caused distantly-related species to develop similar adaptations
16.4, EVIDENCE, CONT age of Earth & fossils
many recently discovered fossils form series that trace evolution of modern species from extinct ancestors
age of Earthevolution takes long timeHutton & Lyell argued Earth was very old, but technology in their day couldn’t tell how old
radioactive dating indicates that Earth is about 4.5 billion years old
recent fossil findsDarwin’s fossil studies convinced scientists life evolved, but hadn’t found enough fossils by 1859 to show evolution of modern species from their ancestors
16.4, EVIDENCE, CONT age, cont
recent finds, contsince Darwin, paleontologists have discovered 100s of fossils that document intermediate stages in evolution of many different groups of modern species
all historical records are incomplete, & history of life is no exception
16.4, EVIDENCE, CONT comparing anatomy & embryology
evolutionary theory explains existence of homologous structures adapted to different purposes as result of descent w/ modification from common ancestor
homologous structures: structures shared by related species & inherited from common ancestor test if structures are homologous by studying anatomical details, how structures develop in embryos, & pattern of appearance over evolutionary history
16.4, EVIDENCE, CONT comparing, cont
homologous, conthomologies (a.k.a. homologous structures) may have different functions
clue to common descent is common structure, not common function
analogous structures: body parts w/ common function, but not structure (doesn’t indicate any relationship)
vestigial structures: inherited from ancestors, but have lost much or all of original function due to different selection pressuresif presence of vestigial structure does not affect organism’s fitness, natural selection would not eliminate it
16.4, EVIDENCE, CONT comparing, cont
embryology: study of development of unborn organisms (in egg or mother’s uterus)early developmental stages of many animals w/ backbones (called vertebrates) look very similar
similarities in embryological development provide evidence that organisms have common ancestor
genetics & molecular biology @ molecular level, universal genetic
code & homologous molecules provide evidence of common descent
all cells use DNA & RNA to carry info from one generation to next & direct ptn synthesis
16.4, EVIDENCE, CONT genetics, cont
DNA, contgenetic similarities are major evidence that all organisms evolved from common ancestors
homologous moleculeshomologous ptns share extensive structural & chemical similarities
homologous ptns in different species have nearly identical DNA sequences
testing natural selectiongather evidence for evolutionary change by
observing natural selection in actionex.: Galápagos finches; Darwin’s proposed that natural selection shaped beaks of bird populations to eat different foods
16.4, EVIDENCE, CONT testing, cont
evidence, contex.: finches, cont
Peter & Rosemary Grant tested this by catch & release studies, documenting changes in food supply each year
found that natural selection takes place in wild finch populations frequently, & sometimes rapidly
16.4, EVIDENCE, CONT evaluating evolutionary theory
evolutionary theory offers insights that are vital to all branches of biology, from research on infectious disease to ecologyevolution is often called the grand unifying theory of the life sciences
evolutionary theory is constantly reviewed w/ new datastill debate important questions, like details of how new species arise & become extinct
significant uncertainty about exactly how life 1st began
remaining questions about how evolution works — not if it occurs
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