BIO120 Fall 2024 Lecture 2 Darwin's Big Idea PDF

Lecture 2 Darwin’s Big Idea and How it Changed Biology 1. Biology Before Darwin & Wallace 2. Darwin, Wallace & the Development of Their Idea...

Lecture 2 Darwin’s Big Idea and How it Changed Biology 1. Biology Before Darwin & Wallace 2. Darwin, Wallace & the Development of Their Idea 3. Darwinian Evolution: A Revolutionary New Model Charles Darwin (age 31; 1809‐1882) Relevant reading in Charlesworth & Charlesworth – Chapter 2 This lecture will be recorded and posted on Quercus. 1 © BIO120 Fall 2024 Biology Before Darwin & Wallace Open Questions in Darwin’s Time 1) Where do species come from? 2) How can we explain complex adaptations? i.e., traits with clear and elaborate function for the survival and reproduction of organisms? 2 © BIO120 Fall 2024 Biology Before Darwin & Wallace The Argument From Design William Paley 3 © BIO120 Fall 2024 Biology Before Darwin & Wallace Paley’s Argument From Design Paley 1802. Natural Theology, or Evidence of the Existence and Attributes of the Deity, Collected from the Appearances of Nature 4 © BIO120 Fall 2024 Biology Before Darwin & Wallace Paley’s Argument From Design Paley 1802. Natural Theology, or Evidence of the Existence and Attributes of the Deity, Collected from the Appearances of Nature 5 © BIO120 Fall 2024 Biology Before Darwin & Wallace Jean‐Baptiste de Lamarck (1744‐1829) First to use the term evolution First to provide a hypothesis for the causal mechanism: – The inheritance of acquired characters 6 © BIO120 Fall 2024 Biology Before Darwin & Wallace The Giraffe’s Neck Lamarck’s example for the inheritance of acquired characters 7 © BIO120 Fall 2024 Biology Before Darwin & Wallace 8 © BIO120 Fall 2024 Biology Before Darwin & Wallace Why Was Lamarck Wrong? August Weismann’s Germplasm Theory (1889) Inheritance only by germ cells (gametes); somatic cells (soma/body) do not function as agents of heredity Thus genetic information cannot pass from soma to gametes and onto next generation Modern interpretation in molecular terms: Genetic information flows in one direction only, from DNA to protein but never in reverse August Weismann 1834‐1914 9 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Darwin AND Wallace Darwin developed first comprehensive theory of evolution Darwin and Wallace independently discovered the chief mechanism of evolution: Natural selection Charles Darwin Alfred Russell Wallace 10 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Darwin’s (and Wallace’s) Theory of Evolution Two major theses: All organisms have descended with modification from a common ancestor (thus, living things change over time) The process leading to evolution is natural selection operating on variation among individuals 11 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea University of Edinburgh 12 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Development of Darwin’s Ideas on Evolution – Exploration Voyage on H.M.S. Beagle around the world (1831‐1836) as ship’s naturalist Intellectual companion to Capt. Robert FitzRoy Made numerous observations and collections of plants, animals & fossils Returned and spent the rest of his life in seclusion at Down House (Darwin family house in Kent, England) developing his ideas, conducting experiments, and writing 25 books Drawing of H.M.S. Beagle by Darwin Photo of Down House by Prof. Stinchcombe 13 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Development of Darwin’s Ideas on Evolution – Gradualism Darwin reads Lyell’s book “Principles of Geology” (1830) Lyell argued for uniformitarianism The forces and processes that shape the Earth’s surface are uniform through time i.e., the forces we see today are the same as previous eons Lyell argued that present day geological processes can explain the history of the Earth Gradualism of erosion, earthquakes, volcanoes, etc. Two implications for Darwin: 1) The notion of a dynamic rather than a static world Charles Lyell 2) Changes build up gradually, by the (1797‐1875) same mechanisms today as in the past 14 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Development of Darwin’s Ideas on Evolution – Species Vary Variation patterns of Galápagos mockingbirds There are 4 similar species endemic to the islands descended from a South American mainland ancestor Darwin doubts fixity of species (March, 1837) 15 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Development of Darwin’s Ideas on Evolution – Struggle for Existence In September 1838, Darwin reads Thomas Malthus’s ‘An Essay on the Principle of Population’ (1798) 16 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Darwin on Malthus “I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved and unfavourable ones would be destroyed.” Charles Darwin (1838) 17 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Wallace on Malthus At the time in question I was suffering from a sharp attack of intermittent fever, and every day during the cold and succeeding hot fits had to lie down for several hours, during which time I had nothing to do but to think over any subjects then particularly interesting me. One day something brought to my recollection Malthus's "Principles of Population", which I had read about twelve years before. I thought of his clear exposition of "the positive checks to increase" ‐ disease, accidents, war, and famine …. It then occurred to me that these causes or their equivalents are continually acting in the case of animals also; and as animals usually breed much more rapidly than does mankind, the destruction every year from these causes must be enormous in order to keep down the numbers of each species, since they evidently do not increase regularly from year to year, as otherwise the world would long ago have been densely crowded with those that breed most quickly. Vaguely thinking over the enormous and constant destruction which this implied, it occurred to me to ask the question, Why do some die and some live? And the answer was clearly, that on the whole the best fitted live. From the effects of disease the most healthy escaped; from enemies, the strongest, the swiftest, or the most cunning; from famine, the best hunters or those with the best digestion; and so on. Then it suddenly flashed upon me that this self‐acting process would necessarily improve the race, because in every generation the inferior would inevitably be killed off and the superior would remain ‐ that is, the fittest would survive. …. The same evening I did this pretty fully, and on the two succeeding evenings wrote it out carefully in order to send it to Darwin by the next post, which would leave in a day or two. I wrote a letter to him in which I said I hoped the idea would be as new to him as it was to me, and that it would supply the missing factor to explain the origin of the species. I asked him if he thought it sufficiently important to show it to Sir Charles Lyell, who had thought so highly of my former paper. from My Life, pp. 360‐363. 18 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Events Leading up to the Publication of the Origin of Species 1831‐1836: the voyage of the Beagle Then 20 years taken up with accumulation and synthesis of evidence for the theory of evolution 1844: Wrote, but did not publish, an essay on natural selection 1856: Began work on natural selection book 19 © BIO120 Fall 2024 Darwin, Wallace & the Development of Their Idea Events Leading up to the Publication of the Origin of Species June 1858: Received Wallace’s article “On the tendency of varieties to depart indefinitely from the original type” July 1858: Linnean Society presentation of Darwin–Wallace paper November 1859: Publication of 490‐page book “On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life” 20 © BIO120 Fall 2024 Darwinian Evolution: A Revolutionary New Model 21 © BIO120 Fall 2024 Darwinian Evolution: A Revolutionary New Model Darwin’s Mechanism of Natural Selection Variation: Individual variation in a population Heredity: Progeny resemble their parents more than unrelated individuals Fitness: Some forms are more successful at (surviving and) reproducing than others in a given environment – i.e., some forms are “more fit” than others Natural selection is heritable variation in fitness 22 © BIO120 Fall 2024 Darwinian Evolution: A Revolutionary New Model (Lamarkian) (Darwinian) 23 © BIO120 Fall 2024 Darwinian Evolution: A Revolutionary New Model Important Elements of Darwin’s Theory 1) Evolution occurs primarily at the level of populations (individuals don’t evolve) 2) Variation is not directed by environment (individuals don’t induce adaptive variation when needed) 3) Most fit type depends on the environment 4) ‘Survival of the fitter’: Evolution works with available variation, and will not necessarily achieve perfection 24 © BIO120 Fall 2024 Darwinian Evolution: A Revolutionary New Model Implications of Darwin’s Theory of Evolution Concept of a changing universe – Replaced view of a static world A phenomenon with no purpose – Natural selection revealed how complex adaptations with important ‘functions’ can arise through an unplanned process 25 © BIO120 Fall 2024 Darwinian Evolution: A Revolutionary New Model Evolution by Natural Selection 26 © BIO120 Fall 2024 Darwinian Evolution: A Revolutionary New Model Treatment with antibiotic Susceptible Resistant Time 27 © BIO120 Fall 2024 Recap Recall: Paley, Lamarck, Darwin, Wallace, Lyell, Malthus, Weissman. Who they are and what they discovered or got wrong. Concepts: Inheritance of acquired characteristics, uniformitarianism, natural selection. Differences, similarities, predictions. Applications: Consider antibiotic resistance evolution under multiple models, and how we would stop the antibiotic resistance 28 © BIO120 Fall 2024 Lecture 3: The Evidence for Evolution 29 © BIO120 Fall 2024