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Descent with Modification: A Darwinian View of Life Part A: Darwin & Natural Selection Theme: Evolutionary change is based on the interactions between populations & their environment which results in adaptations (inherited characteristics) to increase fitness Evolution = change over time in the genetic composition of a population; descent with modification Carolus Linnaeus 1707-1778 Linnaeus: founder of taxonomy; binomial nomenclature Domain – Kingdom – Phylum – Class – Order – Family - Genus – Species (Dear King Philip Came Over For Good Spaghetti) Domains = Eubacteria, Archaea, Eukarya Classification based on anatomy & morphology Cuvier: Paleontologist – studied fossils Deeper strata (layers) - very different fossils from current life Opposed idea of evolution Catastrophism – catastrophe destroyed many living species, then repopulated by immigrant species George Cuvier (1769-1832) Hutton : Gradualism = geologic change results from slow & gradual, continuous process Slow & subtle changes in organisms James Hutton 1726-1797 Lyell: Uniformitarianism = Earth’s processes same rate in past & present (are constant) therefore Earth is very old Charles Lyell 1797-1875 Lamarck: Published theory of evolution (1809- Darwin birth year) Compared living species with fossil forms, found several lines of descent Use and Disuse: parts of body used bigger, stronger (eg. giraffe’s neck) Inheritance of Acquired Characteristics: modifications can be passed on Believed organisms have innate drive to become more complex Importance: Recognized that species evolve, although explanation was flawed Jean-Baptiste Lamarck 1744-1829 Thomas Malthus (1766-1834) Malthus: English cleric and scholar, influential in the fields of political economy and demography More babies born than deaths Consequences of overproducing within environment = war, famine, disease (limits of human pop.) Struggle for existence Charles Darwin (1809-1882) English naturalist 1831 to 1836: joined the HMS Beagle for a 5-year research voyage around the world Collected and studied plant and animal specimens, bones, fossils Notable stop: Galapagos Islands Darwin’s Finch Collection/Tortoise Shell The birds were all about the same size, but the shape and size of the beaks of each species were different. Many islands also show distinct local variations in tortoise morphology… …perhaps these are the first steps in the splitting of one species into several? Darwin waited 30 years before he published his ideas on evolution Alfred Russell Wallace – published paper on natural selection first (1858) Charles Darwin (1859): On the Origin of Species by Means of Natural Selection Mechanism for evolution is Natural Selection Darwin didn’t use “evolution”, but rather “descent with modification” 12 Darwin’s Theory of Natural Selection: 1. 2. 3. 4. 5. Overproduction-Populations produce more offspring than can possibly survive. Overproduction leads to competition. Natural Variation-Individuals in a population vary extensively from each other, mostly due to inheritance. Fitness : struggle to survive, individuals whose inherited characteristics best fit to environment leave more offspring than less fit. Adaptation: enhance an organism’s ability to survive and reproduce Descent with modification- Unequal ability of individuals to survive and reproduce leads to gradual change in population, with favorable characteristics accumulating over generations. Adaptations enhance an organism’s ability to survive and reproduce Eg. Desert fox - large ears, arctic fox - small ears Overproduction of offspring leads to competition for resources Key Ideas: Populations evolve, not individuals. Fitness is determined by the environment. In summary: Natural Selection = Differential success in reproduction Product of natural selection = Adaptations of populations to environment Camouflage (Cryptic coloration) Mullerian Mimicry – Unpalatable mimics unpalatable The Peppered Moth – An Example of Natural Selection Batesian Mimicry – Palatable mimics unpalatable Warning Coloration (Aposematic coloration) Disruptive Coloration Eye spots Counter Shading Natural selection in action Insecticide & drug resistance insecticide didn’t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective Evidence of Evolution 2007-2008 Evidence supporting evolution Fossil record transition species Anatomical record homologous & vestigial structures embryology & development Molecular record protein & DNA sequence Artificial selection human-caused evolution Fossil record Layers of sedimentary rock contain fossils new layers cover older ones, creating a record over time fossils within layers show that a succession of organisms have populated Earth throughout a long period of time Fossil record A record showing us that today’s organisms descended from ancestral species Evolutionary change in horses 550 500 Body size (kg) 450 Equus 400 350 300 250 Merychippus 200 150 Mesohippus Hyracotherium 100 50 Nannippus 60 55 50 45 40 35 30 25 20 15 10 5 0 Millions of years ago Evolution of birds Archaeopteryx lived about 150 mya links reptiles & birds Smithsonian Museum, Washington, DC Land Mammal ? ? ? ? Homologous structures Similar structure Similar development Different functions similarities in characteristics resulting from common ancestry Analogous structures Separate evolution of structures similar functions similar external form different internal structure & development different origin no evolutionary relationship Don’t be fooled by their looks! Solving a similar problem with a similar solution Convergent evolution Flight evolved in 3 separate animal groups evolved similar “solution” to similar “problems” filling similar ecological roles in similar environments, so similar adaptations were selected (similar niches) analogous structures, not closely related Convergent evolution Fish: aquatic vertebrates Dolphins: aquatic mammals similar adaptations to life in the sea not closely related Those fins & tails & sleek bodies are analogous structures! Vestigial organs Modern animals may have structures that serve little or no function remnants of structures that were functional in ancestral species deleterious mutations accumulate in genes for non-critical structures without reducing fitness snakes & whales — remains of pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone and Comparative embryology Similar embryological development in closely related species all vertebrate embryos have similar structures at different stages of development gill pouch in fish, frog, snake, birds, human, etc. Evidence for Evolution Comparative Embryology- The complete picture Molecular record Comparing DNA & protein structure universal genetic code! DNA & RNA compare common genes cytochrome C (respiration) hemoglobin (gas exchange) Human/kangaroo Closely related species have sequences that are more similar than distantly related species DNA & proteins are a molecular record of evolutionary relationships Nucleotide substitutions 100 Dog/ cow 75 Human/ cow Rabbit/ rodent 50 Horse/ donkey Llama/ cow Horse/cow Sheep/ goat 25 Human/rodent Pig/ cow Goat/cow 0 0 25 50 75 100 Millions of years ago 125 Artificial selection Artificial breeding can use variations in populations to create vastly different “breeds” & “varieties” “descendants” of wild mustard “descendants” of the wolf Natural Selection Artificial Selection •Nature decides •“Man” decides •Works on individual •Selective breeding •Inbreeding occurs •eg. Finch beaks •eg. Breeds of dogs Evidence for Evolution Direct Evidence Rapid Evolution Strains of bacteria becoming resistant to antibiotics Weeds and herbicides Insects and insecticides Life has changed over time & in turn has changed the Earth Living creatures have changed Earth’s enviro making other life poss Essence of Darwin’s ideas (1) Variation exists in natural populations (2) Many more offspring are born each season than can possibly survive to maturity (3) As a result, there is a struggle for existence - competition (4) Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the average characteristics of the population - adaptations (5) Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species