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Download Chapter 2: Variation Under Nature_On the Origin of Species - Arantxa Lu-ong
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SPECIES VS. VARIETY Variation Under Nature Variability • Monstrosities • Variations - Environment and Heredity • Not all variations are inheritable. Individual Differences • Frequently appear in the offspring from the same parents. • Important to Darwin since it can be inherited and materialize natural selection. • Polymorphic Genera - Species with inordinate amount of variation. Hieracium Hieracium umbellatum (Narrow-leaf hawkweed) Hieracium murorum (Wall hawkweed) Hieracium Hieracium venosum (Rattlesnake hawkweed) Hieracium horridum (Shaggy hawkweed) Hieracium Hieracium paniculatum (Panicled hawkweed) Hieracium pilosella (Mouse-ear hawkweed) Hieracium Hieracium scouleri (Hounds tongue hawkweed) Hieracium triste (Woolly hawkweed) Doubtful Species • Inconsistencies in classification of species. • Disagreements between well known zoologists and naturalists. Doubtful Species • Mr. H.C. Watson - 182 British Plants (Varieties) • Mr. Babington - 251 species • Mr. Bentham - 112 species Doubtful Species • North America & Europe - Birds and Insects • Galapagos Archipelago and S. American Mainland - Birds • Mr. Wollaston - Insects in islets of Madeira (Varieties) Doubtful Species • British red grouse Wide Ranging, Much Diffused & Common Species Vary Most • Alphonse de Candolle et al. - Wide ranging plants presents several varieties. • Much diffused and common species give rise to well-marked varieties. Species of Larger Genera Vary More Than Smaller Genera • Larger Genera - Include many species and constituted mostly by dominant species. • Fresh-water and salt-loving plants - Wide ranges and much diffused. Species of Larger Genera Vary more than Smaller Genera • Species of larger genera in each country present more varieties than species of smaller genera. • More species = More varieties • Theory of Creation is flawed. Many Species of Larger Genera Closely Resemble Varieties with Restricted Ranges • The species of the larger genera resemble varieties, more than do the species of the smaller genera. Many Species of Larger Genera Closely Resemble Varieties with Restricted Ranges • Varieties and closely allied species have restricted ranges. • Mr. H.C. Watson (London Catalogue of Plants): 63 species = 6.9 provinces 53 varieties = 7.7 provinces (Species = 14.3 provinces) Many Species of Larger Genera Closely Resemble Varieties with Restricted Ranges • The amount of difference is important in classifying organisms to either species or varieties.
