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Evolution - constancy & change Modern Evidence for Natural Selection 1. 2. 3. 4. 5. 6. fossil records – organisms change over time biogeography – related organisms in same area comparative anatomy – homologous structures comparative embryology – similar embryos molecular biology – similarities in DNA, proteins artificial selection – selective breeding Phylogeny & Molecular Systematics • Phylogeny – study of evolutionary relationships • Molecular Systematics – study of molecular structures (DNA, protein) to determine evolutionary relationships *animals, including humans, and fungi, are more closely related to each other than either are to plants Occam’s Razor & Parsimony • Occam’s Razor (law of parsimony) - "All other things being equal, the simplest solution is the best." • Used to justify a phylogenetic tree that represents the smallest number of evolutionary changes Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Cladogram (phylogeny) - shows ancestral relationships Comparison of hemoglobin Cladogram - primate DNA comparisons Molecular Systematics Molecular Clocks • DNA or protein comparisons to estimate the length of time that two species have been evolving independently Primate evolution • Humans have 99.99% similarity • Humans and chimps have 98% similarity “Ontogeny recapitulates Phylogeny" The embryonic development of a species (ontogeny) is a replay of its evolutionary history (phylogeny). - 1866 Ernst Haeckel Comparative Embryology (faked) Drawings vs. photographs Comparative Anatomy Animal developmental characteristics p.371 •body plan •symmetry •body cavity •digestive tract •segmentation mono-, para-, or polyphyletic monophyletic – all descendants paraphyletic not all descendants polyphyletic - last common ancestor is NOT within group Monophyletic includes the most recent common ancestor of a group of organisms and all of its descendants Polyphyletic does not include the common ancestor Paraphyletic includes most recent common ancestor, but not all of its descendants Restriction Maps 4 3 10 13 17 17 1. Gibbon is least similar; chimp is most similar. Skull Morphology deer cat dog bear gorilla human brain size teeth types herbivore brain to face ratio meat-eaters mammals Skull Morphology deer cat dog bear gorilla human brain size teeth types herbivore brain to face ratio meat-eaters mammals Restriction Maps 2. Changes will go back and forth as environment changes. 3. Neutral changes will accumulate. 4. Advantageous changes will accumulate more often. 5. Two closely related organisms will have fewer genetic differences. Animal Development & Phylogeny Animal developmental characteristics p.371 •body plan •symmetry •body cavity •digestive tract •segmentation Tissue Organization 1. no tissue - no specialized fxn 2. tissue - specialization Body Symmetry 1. radial - looks same cut from any side at top 2. bilateral - looks same cut from 1 side at top Body Cavity 1. acoelomate - no body cavity, digestive tube connected to muscle 2. pseudocoelomate - partial cavity 3. coelomate - digestive tube separated from muscles Digestive Tract 1. protostome - spiral cleavage - blastopore-->mouth 2. deuterostome - radial cleavage - blastopore-->anus http://www.mun.ca/biology/scarr/141993_Protostome_vs_Deuterostome.jpg..jpg Comparative Embryology • closely related organisms go through similar stages in their embryonic development *all vertebrate embryos have gill slits: – gill slits in fish form gills – human gill slits form the Eustachian tubes connecting the middle ear with the throat Comparative Anatomy Vestigial Structures – pelvic bones in whale - eye sockets in blind salamanders Convergent Evolution -similar solutions to similar “problems” Analogous structures • similar functions, no evolutionary relationship; different internal structure & development *flight - bird vs bat vs insect *reproduction - marsupials vs placentals *aquatic vertebrates - dolphins vs fish Artificial selection • breeding Artificial selection • pesticide resistance • antibiotic resistance Natural Selection “survival of the fittest”? Charles Darwin • (1809-1882) British naturalist • 1831-1836 Voyage on HMS Beagle • collected specimens of fossils as well as living; observed the various adaptations of plants and animals • breeding experiments • 1859 “On the Origin of Species by Means of Natural Selection” “Origin of Species” Key Points 1. descent with modification • all species evolved from ancestral species and were not specially created; diverse modifications accumulated over millions of years 2. natural selection • mechanism of evolution; a consequence of interactions between individual organisms and their environment Natural Selection Requires… 1. Variation - individuals within a population show variation in their characteristics 2. Overproduction / competition environmental resources are limited 3. Survival / reproduction – only those best suited to environment will survive to reproduce and pass on favorable variations Historical Views of Origin of Life Creationism (Judeo–Christian): Earth is ~6000 years old and was populated by unchanging life forms made by the Creator during a single week Greek philosophy (Aristotle ~350 BC): scala naturae (scale of increasing complexity) – species were fixed in form, did not evolve Carolus Linnaeus • (1707 – 1778) Swedish physician, botanist • father of taxonomy — developed the binomial nomenclature system • organized organisms into categories based on similar physical features James Hutton • (1726-1797) Scottish geologist • proposed geological gradualism – change is the cumulative product of slow, continuous processes *canyons are formed by erosion from rivers Georges Cuvier • (1769-1832) French anatomist • founder of paleontology – study of fossils • proposed catastrophism – periodic catastrophes result in mass extinctions; migrating species repopulate the area Charles Lyell • (1797-1875) geologist • “Principles of Geology” proposed uniformitarianism – geological processes are uniform and balanced throughout Earth *processes that build mountains are eventually balanced by the erosion of mountains by wind and water Jean Baptiste Lamarck • (1744-1829) naturalist • evolution is driven towards complexity and perfection (organisms became better adapted to their environments) • 1809 proposed inheritance of acquired characteristics: – use and disuse *giraffes Reverend Thomas Malthus •(1766-1834) studied human overpopulation: 1. all species over-produce 2. competition for resources 3. only a fraction survive to reproduce 4. eventually populations reach carrying capacity Stephen Gould • 1972 proposed theory of punctuated equilibrium - based on fossil record: little change occurs, then rapid localized speciation occurs • exaptation – shifts in function of a trait during evolution *mammalian limb Michael Behe • 1992 irreducible complexity (argument for intelligent design) – biological systems are too complex to have evolved through natural selection – evolutionary pathways may contain one or more unselected steps The Subtleties of Natural Selection • • • individuals do not evolve; populations do only heritable variations can be changed an adaptation to a set of conditions may be useful or detrimental, under different circumstances Modern Examples of Natural Selection • Kettlewell - observed peppered moths • Grants on the island of Daphne Major observed shifts in the frequency of beak sizes over short periods of time • Antibiotic resistance in bacteria • How do genetic variations arise in nature? Industrial Melanism – Peppered Moths •1848 Kettlewell’s observations – moths are darker in polluted areas 1973 Grant - change in finch beak size