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Zoology: Chapter 6 Pre-Darwinian Evolutionary Theories No set theory: based mainly in mythology and superstition Early Greeks Xenophanes, Empedocles, and Aristotle Studied fossils and realized that they were evidence for former life but failed to establish a real theory Mid 1600’s – Archbishop Ussher established Earth’s creation at 4004 B.C Georges Buffon, mid 1700’s, established the idea of changes in species and extended Earth’s age to 70,000years Lamarckism: First Theory Jean Baptiste de Lamarck, late 1700’s, early 1800’s, came up with the first written theory of evolution. Proposed inheritance of acquired characteristics Organisms, by striving to meet the demands of their environments, acquire adaptations and pass them by heredity to their offspring Giraffe’s neck length Lamarckism cont. Lamarck’s theory was transformational Suggests individual organisms can change characteristics to produce evolution Transformational theories are now rejected Darwin’s theory is variational Based off genetic variation in species Evolutionary pressures have caused differential survival and reproduction among species Charles Lyell and Uniformitarianism Sir Charles Lyell British Mid 1800’s Geologist Theory of uniformitarianism Laws of chemistry and physics remain the same throughout history Past geological events occurred by natural processes similar to those observed today Helped establish that Earth was millions of years old Assignment Pg. 129 Questions 1 and 2 Read textbook pg. 103-106 for discussion tomorrow. Darwin’s Voyage Darwin sailed on the Beagle, a British ship Journey began on Dec. 27, 1831 and lasted roughly 5 years (1836) Darwin was 23 years old when the trip began The goal of the voyage was to survey South America and the Pacific This became one of the most important voyages of the 19th century Voyage continued During the voyage the Beagle stopped at many ports and harbors along South America, Australia, and the Pacific. Darwin made collections of Fossils and made observations about the flora and fauna of the areas He started to notice many similarities between different areas and the species there Arrives at the Galapagos Islands September 1835, the Beagle arrived at the Galapagos Islands, small island chain off the Pacific Coast of South America (near equator) Darwin stayed 5 weeks on the islands He made observations of giant tortoises, marine iguanas, mockingbirds, and of course, finches All of these observations changed his thinking and led to the beginnings of his theory on evolution. How Darwin arrived at his theory Darwin compared the flora and fauna of the Galapagos and the Cape Verde islands, which he too visited. He noted they were similar in climate and topography, but vastly different in the plants and animals that inhabited the islands He came to conclusion life originated in South America, spread, and adapted to each different climate and environment Darwin said the observations were “origin for all my views” The Voyage ends The Beagle returned to England on October 2, 1836 and Darwin conducted the rest of his research there 3 years after the return, his journal was published He released On the Origin of Species 20 years later Side note: Darwin was a weird dude; he also married his cousin in 1839 Assignment Pg. 129 Question 3 Answer in a well written, grammatically correct paragraph of 5-10 sentences On the Origin of Species Darwin’s theory Perpetual Change Common Descent Multiplication of Species Gradualism Natural Selection Perpetual Change The world is constantly in a state of change Fossil record is evidence of this Change is both Earth’s environment over time, as well as shifts in species across Earth’s history Single celled to Fish to Reptiles to Mammals, etc The Fossil Record Fossil record is biased because preservation is selective Some animals do not leave behind many or any fossils (jellyfish), where as vertebrates and things with shells leave behind many fossils Also some layers of fossils have been eroded or broken apart by geologic processes High heat also destroys fossils Geologic time Relative dating has been used for ages, even before Earth’s age was known Now use radiometric dating (potassium-argon 40 ) typically to determine the ages of fossils. Based on half-life of Potassium to degrade to Argon Can date fossils back millions of years. Back to Precambrian time even Evolutionary Trends Fossil record lets us study evolutionary change across long periods of time We have found Animal species typically survive 1-10 million years, but this is highly variable Across this time frame, the replacement of the taxa and changes in species are observed Horses are a great example: Common Descent Darwin proposed all plants and animals arose from a single ancestor Phylogeny is the study of this “tree of life” Pre-Darwin: multiple theories of origin According to Darwin’s theory, one should be able to trace their lineage back to a single celled microbe that lived long ago Homology and Phylogenetic Reconstruction Homology: similar organs in different species arose from a common organ and have just been modified to fit the niche of the animal Limbs of vertebrate are a prime example Homology continued Darwin’s book The Descent of Man and Selection in Relation to Sex used anatomical comparisons of Man to Apes to suggest a common ancestral lineage Homologues are prime evidence for common descent. They form the basis for phylogeny and the tree of life. They are so common in the living world. Ontogeny, Phylogeny, and Recapitulation Ontogeny is the study of the development of an organism throughout its life. Evidence for homology/common descent Recapitulation/biogenetic law Ernst Haeckel: studied embryos and gave us this statement: Ontogeny recapitulates phylogeny or in simple words: Individual development repeats evolutionary descent Ontogeny continued Later von Baer, furthered the statement but said that the homologies early in development are more similar in species, however development plays a big role in the final “make up” of the creature. Animals with simple life cycles look closer to their developmental stage than do those with long complex life cycles Multiplication of Species This is common sense with evolution. Darwin believed that species separated by some geographic features was the pressure needed for new species to be produced Interesting is that we can find where new species divulge but the mechanism of how is still very unknown. What is a “species” Descent of all members from a common ancestral population Reproductive compatibility (they can interbreed) Maintenance within species with genotypic and phenotypic cohesion ( lack of abrupt differences between population in allele frequencies and characteristics) Now back to…….. Speciation = species formation Reproductive barriers prevent species from interbreeding Arise gradually over long periods of time Allopatric vs Sympatric Speciation Allopatric Speciation Arises because of geographical separation of two species that could interbreed The 2 separated groups adapt and evolve and reproduce at different rates, thus eventually forming new species Vicariant Speciation – geographical event separates. Faulting, Mountains forming Founder Event – few members leave a larger population and settle elsewhere Allopatric Speciation Vicariant speciation Consequences: Ancestral population is fragmented, however fragments typically left intact. Does not directly induce evolution though. Other factors are needed Can divide several species simultaneously Effects numerous and diverse species most Allopatric Speciation Founder event Migration of a small group to an area where no members of their population are living Fruit flies Greatly reduces gene pool because of small population size Certain traits can be expressed or deleted Nonallopatric Speciation Can a species ever arise without a geographical barrier? Speciation in lakes of Africa Sympatric speciation Says that individuals within a species become specialized for occupying different components of the environment Or: By occupying different niches, members of a species acquire enough adaptations to create reproductive barriers Happens a lot in plants: Polyploidy in flowering plants Adaptive Radiation A.R. – production of ecologically diverse species from a common ancestral stock Examples: volcanic islands, Galapagos Is. Essentially void of life at the beginning. Darwin’s finches Allows for many founder events because each island is distinct in what plants inhabit it, etc Gradualism Opposes arguments for sudden origin of species Suggests that changes occur over numerous generations and very slowly. No sudden changes Populational gradualism vs. phenotypic gradualism Pop. Grad states that traits become established in a population by increasing their frequency in the population Phenotypic grad. States that new traits, even those strikingly different from ancestral ones, are produced in a series of small steps Phenotypic Gradualism Highly controversial Did not account for mutations “sport” mutations were viewed as always negative Issues of “selective breeding” vs natural causes controversy over phenotypic gradualism still Punctuated Equilibrium Alternative to phyletic gradualism: long term constant change Not fully supported by fossil record P.E. explains discontinuous evolutionary changes observed throughout geological time Says that speciation events occur in a geological instant Allows plenty of time for Darwinian evolution to occur still Natural Selection Explains the origins of adaptations based upon 5 observations Explains: all developmental, behavioral, anatomical, and physiological attributes Pg. 118-119 in text. Oppositions to Natural Selection Natural selection has been challenged for years Orthogenesis – claims that directed (nonrandom) variation governs evolution Variation has momentum that forces lineage to evolve in a particular direction that is not always adaptive Irish Elk and antler size Genetic research disproved this challenge More challenges to Darwin Biggest issue: NS cannot generate new structures or species; only modify previously existing ones Some early structures could not have performed the function that their fully formed structures do, thus unexplained how they are favored ?? Some structures evolved for another purpose then they are used for today Neo-Darwinism Adds mechanism of inheritance Population genetics and Darwin made a major impact in the 1930’s in modifying the theory Microevolution Macroevolution Microevolution Study of genetic change occurring within natural populations; observation of polymorphism in the gene pool Potential alleles can be enormous due to mutations rates Genetic Equilibrium Why haven’t recessive traits like blonde hair, O blood type, etc disappeared totally Hardy-Weinberg equilibrium states that heredity alone does not produce evolution; In two parent populations, the allelic frequencies and genotypic ratios attain an equilibrium in on generation and remain constant thereafter, unless……….disturbed? How to Upset Genetic Equilibrium Random Genetic Drift Nonrandom mating Recurring mutations Migration Natural Selection A combo of any of these Genetic Drift Chance fluctuation in allelic frequencies from one generation to the next; can result in the loss of alleles from a population Occurs in finite populations; small populations Harmful to evolution because it restricts possible genetic responses to environmental change Ex: Cheetahs: very little genetic variation Stem from a very small population; can cause struggle to survive Nonrandom mating Selective breeding for certain traits Throws off Hardy – Weinberg equilibrium Albinos with albinos (rare mutation) Done in dogs often (tea cup species) Inbreeding Increases homozygousity however increases chances of rare genetic mutations to become homozygous and expressed Mutations Screw ups in the coding of your DNA Can cause things from vitaligo to Tay-Sachs to Down’s Syndrome, etc Most mutations are missense (not expressed); however some can be harmful Migration If you divide a large population into smaller populations, then genetic drift and selection can cause evolutionary divergence of that population; however, small amounts of migrations keeps the species from becoming too distinct genetically Interactions of all these…… Produces populations that are evolutionary and qualitatively different then those predicted by Hardy-Weinberg Produce populations that are different then if you remove the factors…..duh!!! Hardy Weinberg equilibrium does not exist for any significant period of evolutionary time Macroevolution Major Evolutionary Change!!!! Gould suggested 3 tiers of times to observe evolutionary processes. Tier 1: 10’s to thousands of years; the timescale of population genetic processes Tier 2: millions of years; covers time scale on which rates of speciation and extinction can be measured Tier 3: covers 10’s to 100’s of millions of years; marked by periods of mass extinctions. Speciation and Extinction through Geologic Time According to Darwin, each species has 1 of 2 fates: give rise to another species or become extinct. Rates of speciation and extinction vary, but those with highest rates of speciation and lowest rates of extinction produce the greatest diversity of living things. What traits lead to higher rates of speciation and greater resistance to extinction?? Species Selection Cover a variety of traits and encompass survival and multiplication of species among different lineages. Mating rituals Social structuring Migration patterns Geographic distribution Descendent species will resemble their ancestors in these species level traits Species Selection Differential rates of speciation and extinction can be caused by variation in organismal-level properties Ex: generalized vs. special feeding Specialized eaters would migrate more, and be subjected to higher rates of geographic isolation This means higher rates of speciation, however also higher rates of extinction. Mass Extinctions Mass Extinction – period where large numbers of taxa go extinct simultaneously. Occur at a rate of approx. 26 million years 5 Major Mass Extinctions Ordovician – 430 m.y.a. Devonian – 350 m.y.a. Permian – 225 m.y.a. Trassiac – 200 m.y.a Cretaceous – 65 m.y.a. Mass Extinctions Permian 225 million years ago ½ of shallow-water inverts disappeared 90% of marine inverts disappeared Occurred in just a few million years Cretaceous 65 million years ago Killed all dinosaurs, as well as some marine inverts, and other small reptiles. Assignment P. 129 Question 22 Compare and Contrast Microevolution and Macroevolution 1 paragraph (grammatically correct, correct punctuation, ect.)