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Chapter 22 Notes.pdf

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Concordia University
BIOL 226
Robert Weladji

CHAPTER 22. DESCENT WITH MODIFICATION: A DARWINIAN VIEW OF LIFE • Organisms are well suited to their environments • i.e. great adaptations to surrounding environments Overview • Darwin was fascinated with “endless forms most beautiful” • On November 24, 1859, the day Charles Darwin published this book • A new era of biology, the era of evolutionary biology, began • The Origin of Species focused biologists’ attention on the great diversity of organisms Evolution • Evolution can be defined by Darwin’s phrase descent with modification • i.e.? • Darwin noted that current species are descendants of ancestral species that were different Prevailing view before Darwin publication of the Origin? • The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species Pre-Darwinian Views: (1) Aristotle (384-322 BC) • Species are fixed • Scala naturae: ? • “Affinities” among organisms – arranged on a ladder or scale (the ladder of life) (2) Natural Theology • Adaptations: evidence of the Creator’s design (CREATIONISM) • Analogy of the watch – William Paley • Good design implies an intelligent designer • Watchmaker of life - God The Blind Watchmaker • Richard Dawkins • Fallacy: good design does not imply foresight • Natural selection is the designer of life • Blind watchmaker of life Fig. 22.3 - Ideas About Change over Time • The study of fossils helped to lay the groundwork for Darwin’s ideas • Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata 1 Lamarck (1744-1829) • A full theory of evolution: species evolve • Mechanisms? – Two principles: • Use & disuse • Inheritance of acquired characteristics (Fig 22..4) The Voyage of the Beagle • Voyage of the Beagle: Darwin collected specimens of South American plants and animals • He observed adaptations of plants and animals that inhabited many diverse environments Darwin’s Focus on Adaptation • Darwin perceived adaptation to the environment and the origin of new species as closely related processes • From studies made years after Darwin’s voyage, biologists have concluded that this is indeed what happened to the Galápagos finches (Fig 22.6) Evolution: defined • “…all of biological history, from the earliest microbes to the enormous diversity of modern organisms…” (C & R 2002) • “All the changes that have transformed life on Earth from its earliest beginnings to the diversity that characterizes it today.” (glossary: C & R 2005) • “…descent with modification…” (Darwin) • Change in the genetic composition of a population from generation to generation Descent with Modification • The phrase descent with modification summarized Darwin’s perception of the unity of life • The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past • In the Darwinian view, the history of life is like a tree with multiple branching from a common trunk out to the tips of the youngest twigs (representing life’s diversity) – • Fig. 22.7 & 22.8 Darwin’s Theory: Evolution by Natural Selection • Species were not created in their present forms, but evolved from ancestral species • How adaptations arise? • Mechanism for evolution: natural selection • NS=? • A process in which individuals with certain inherited traits leave more offspring than individuals with other traits Artificial Selection, Natural Selection, and Adaptation • Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection 2 • Darwin then described two observations of nature and from these drew two inferences Darwin’s 2 observations • Observation #1: Members of a population often vary greatly in the
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