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Transcript
Evidence of Evolution Emergence of Evolutionary Thoughts A Theory Takes Form Evidence from Fossils Evidence in Body Form Influential Geological Forces Evolution: in the broadest sense of the term, refers to change or growth that occurs in a particular order In biology, evolution refers to the processes that have transformed life on Earth from its earliest forms to the vast diversity that we observe today/ heritable changes Microevolution: generation-to-generation changes in a population’s allelic or genotypic frequencies Macroevolution: large-scale evolution occurring over very long periods of time At or above species level Formation of new taxonomic groups Aristotle (Ancient Greece): species are fixed and do not evolve All forms of life arranged on a scale of increasing complexity/ Continuum of organization (Natural Scale of Life) Insects and small animals were at the bottom, and humans sat at the top 19th Century Expeditions out of Europe Extensive observations of nature in the 19th century did not fit with the prevailing belief systems Cumulative findings from biogeography, comparative morphology and geology led naturalists to question the traditional ways of interpreting the natural world Biogeography The study of patterns in the geographic Emu/ Australia distribution of species Rhea/ South America Ostrich/ Africa Comparative morphology Ø The study of anatomical patterns Ø Problematic in classifying organisms that are outwardly very similar, but quite different otherwise/ reproductive parts Vestigial structures Ø Body parts that have no apparent function/ tail bones in humans Fossils Ø Physical evidence of organisms that lived in the ancient past Ø Deeper layers held fossils of simple marine life Ø Layers above held similar but more complex fossils George Cuvier Ø Assumed Earth to be thousands, not billions of years old Ø Proposed theory of catastrophism to explain extinction Jean Baptiste Lamarck Ø Advocated that life evolves (changes in the line of descent) Ø Proposed that environmental pressures cause an internal need for change Ø Proposed inheritance of acquired characteristics Ø Change occurs through use and disuse of body parts Charles Darwin The Voyage of the Beagle (1831-1836)/ expedition to South America Ø Observed and collected specimens of the exotic and diverse faunas and floras of South America Ø Noted that the plants and animals on the continent had very unique characteristics, very distinct from those of Europe Ø Species on the Galapagos islands are found nowhere else in the world Ø Species unique to different islands Ø Species similar but not identical to species on nearby mainland (but quite different from animals on far mainland) Charles Lyell: The Principles of Geology “Uniformity Theory” “Gradualism” / Earth had changed slowly, and what we see today is the result of gradual changes (over millions of years) Thomas Malthus Ø Correlated decreases in the size of human populations with episodes of disease, famine and war Ø Proposed idea that humans can run out of resources Ø Human reproduction can exceed capacity of environment to sustain them Back to Darwin After the Voyage of the Beagle Reassessed all observations made during the voyage By early 1840s, wrote a manuscript describing the major features of his theory of evolution by natural selection, but never published Alfred Russel Wallace Developed his theory about evolution by natural selection independently from Darwin based on his work in Indonesia (1858) “On the Origin of Species by Means of Natural Selection” Charles Darwin (1859) Darwin’s Theory of Evolution Darwin’s main idea: living species have descended from earlier life-forms and that species change over time/ Descent with modification Darwin proposed natural selection as the mechanism by which evolution occurs Natural selection occurs within populations Individuals of natural populations vary in fitness/ degree of adaptation to an environment, as measured by genetic contribution to future generations Results in adaptation of organisms within a population to their environment Adaptive trait: a heritable trait that enhances an individual’s fitness to an environment Natural selection can be defined as differential success in survival and reproduction within a population Fossils as Evidence of Evolution Preserved remains of organisms that lived in the past Document the differences between past and present organisms and the fact that many species became extinct Formed in different ways Most fossils are mineralized bones, skulls, teeth Casts or mold fossils: Created when an organism is buried and decays The empty hole where the organism was is filled in with sediments or minerals Trace Fossils: Fossils of an organisms activity Footprints, burrows, tracks Some fossils retain organic material Ø Fossilized leaves contain remnant chlorophyll Ø Insects in amber (fossilized resin) Petrification: remains of dead organisms turned to stone through the replacement of the original organic material with minerals Petrified tree Fossil Record History of life as documented by fossils The sequence in which fossils appear within layers of sedimentary rocks (the strata) provides the strongest evidence of evolution Will never be complete Ø geological events Ø slanted toward species with hard parts How Is The Age of Rocks and Fossils Measured? Radiometric dating Ø Half-life: the time it takes for half of the atoms in a sample of radioisotope to decay How Has Earth Changed Over Geologic Time? Continental Drift (1900’s) Movement of the Earth's continents relative to each other by appearing to drift across the ocean bed 250 million years ago, plate movements brought all the land masses together into a supercontinent: Pangaea 180 million years later, Pangaea broke apart Plate Tectonics Theory (1950’s) Explains how continents move Earth’s crust divided into giant irregular shaped plates that essentially float on the mantle causing the continental drift Plates moving away from each other Plates sliding past each other/ earthquakes Plates colliding/ mountain ranges San Andreas Fault in California/810 miles Pacific plate and North American plate Continental Drift Reshaping of the physical environment and climate Altering the habitats in which organisms live Species extinction and new opportunities Explain why similar animal and plant fossils are found on different continents Evidence of Evolution Ø Morphological divergence Ø Morphological convergence Ø Comparative embryology Ø Molecular biology Morphological Divergence Anatomical similarities between species reflect common descent Homologous structures (different use, similar structure) are variations on an anatomical structure of an ancestral organism Remodeling of structures to fit certain functions, descent with modification Forelimbs Morphological Convergence Analogous Structures Do not infer evolution Similar functions, different structures Evolved independently Comparative Embryology All organisms of a group have similar development Same master gene directing development