9/11/14 Darwin’s Theory of Evolution Charles Darwin “Nothing in biology makes sense except in the light of evolution” • Synthesized these areas to establish -Theodosius Dobzhansky modern evolutionary biology. • Most important theory in biology. • Provides loose framework for this course. The History of Evolutionary The Old World View Thought • What led Darwin to conclude that • Plato & the Essence organisms evolve and are related by • Philosophical view descent? that all things have an essence, or type. • Old World View • Individuals are a • The enlightenment deviation from this • The lead-up to Darwin type. • Darwin 1 9/11/14 Ptolemy & geocentrism Aristotle & the Scala Naturae Coincided nicely with humans as the center of the universe • Life arranged in a scale from simple to complex with humans on top. • Developed the idea of a ‘final cause’ to explain everything. • Everything served a purpose to strive toward perfecon. The Renaissance & Revolutions The Judeo-Christian tradition • Increased wealth allowed for increased freedom to stray from the dictates of authority (especially in Italy). • Formalized/instuonalized all of this. • The world was geng smaller! – Discovery of the New World. • Final purpose was to glorify – People began to realize that the world was not exactly the way they were God. told that it was. • Humans (and the universe) – Again, a challenge to authority. were created perfectly, • Followed closely by the Reformaon. therefore any suggeson of – Again, a fundamental challenge to The Authority. evolu.on was heresy. – All of these caused certain people to begin thinking outside of dogma. • World was young (origins – Including challenges of dogma in observaons of the physical world. described in the bible). – E.g. Copernicus & Galileo & Heliocentrism, Newton and modern physics. • Unchanged for 5,000 years. • Followed by Revoluons: English, American, French. All challenges to authority. 2 9/11/14 Evolution before Darwin Evolution before Darwin (Charles, that is) (Charles, that is) • Carl Linnaeus • George Cuvier published Systema • Father of paleontology Naturae in 1796. • Noted decreasing • Hierarchical similarity to modern classification of living fauna as found deeper organisms. and deeper strata. • Still essentialist, but • Established extinction insights into unity of life. as fact • Catastrophism Evolution before Darwin Evolution before Darwin (Charles, that is) (Charles, that is) • Erasmus Darwin • Jean Baptiste de publishes Zoonomia Lamarck publishes 1794. Theory of Inheritance of • Suggests unity of life Acquired and recognizes the Characteristics in 1801. struggle for existence • First proposal of as cause of evolution. mechanism of • Charles Darwin’s evolution. grandfather. • Died poor and obscure. 3 9/11/14 The Voyage of the Beagle Darwin: Early influences 1831-1836 • Born 1809. Natural History all the rage during childhood. • Hated medical school. • Became involved with premier naturalists of the day and studied numerous diverse taxa. • Educated during a scientific revolution that placed the sciences (including biology) into the realm of physical, not meta-physical explanations. • Finally, he found theology too boring. • Earth is a steady-state system. Uniformitarianism • Events in the past were the same as those occurring in the present day. • Principle originally • Fossils were laid down as sediments slowly proposed by James accumulated in areas of deposion; Hutton. • Exposed sediments were subjected to • Developed and erosion. Endless cycle of subsidence and argued by Charles sedimentaon, followed by uplifing and Lyell (1830). erosion. • Contrasted against • Organisms became exnct and were castrophism. replaced. 4 9/11/14 Observations The Origin of Species • Geological upheaval at the Cape Verde Islands & Chile • Main theses: • The fossil record • (1) characters of • Biogeography species are not fixed. • (2) natural selection is the agent of change. • (3) all organisms are related by descent. Theory of Natural Selection Characters of species are not fixed • Variation under • Influenced by domestication. Thomas Malthus’s • Variation in nature. Essay on the Principle of • Variation heritable. Population (1798). 5 9/11/14 Necessary and sufficient condions for All organisms related by descent natural selecon • There is variaon in the populaon in that trait. • The variaon must have some genec basis. • New variaon is created all the me. • There are limits to populaon growth. • Variaon in that trait is correlated with ‘reproducve success’. Darwin’s biggest dilemma… Darwin’s biggest dilemma… • First edition, • Blending inheritance admitted profound incompable with ignorance on natural selecon. mechanisms of • Variaon eliminated, inheritance. not preserved. • Later editions, • Evoluon would be introduced blending driven by mutaon, inheritance and use not natural selecon. and disuse of structures. 6 9/11/14 Darwin’s challenges Darwin’s challenges • The absence of • Evolution of organs intermediate forms. of extreme – Competition and perfection. extinction. – Numerous transitional forms – Taphonomy and found in other incompleteness of organisms. fossil record. – Given time and power of NS, could go through these forms. Darwin’s challenges Darwin’s challenges • The evolution of • Production of new instinct (especially species. sterile individuals) • Noted that species • Variation in were not discrete behavior, as well. entities. • Could operate at • Gradation between higher level than varieties and individual. species not distinct. 7 9/11/14 Logical consistencies Logical consistencies • Earth must be very • Fossils should show old. logical transitions. • Given rates of • Recent fossils more deposition, estimated similar to present-day an age of hundreds of fossils than older, millions of years. deeper fossils. • Logical transiitons from fish to amphibian to reptile and mammal. Logical consistencies Logical consistencies • Geographic distribution. • Boundaries determined by • Geographic limits to dispersal. distribution. • Distribution of organisms • Present distribution on islands. determined by – Bats only terrestrial geography, not mammals on oceanic islands. physical conditions. – No amphibians on oceanic • Adaptations islands. – Island species show clear determined by affinities with mainland physical conditions. species. 8 9/11/14 Logical consistencies What came next • Structure and development. • Darwin hesitated to – Homology (features publish. Finished book sharing identity by in 1844. descent). • Didn’t publish. – Embryonic development. • Correspondence from A.R. Wallace. – Rudimentary organs. • Both submied papers to the Linnaean society. • In 1859 published The Origin of Species Understanding Natural Selection Natural Selection, considerations 1. Individuals in a population vary in their • Newly created variation (mutation) characteristics and these variations are heritable. must be random with respect to need. 2. New variation is created generation after • Otherwise mutation drives evolution, generation. 3. Parents produce on average more offspring and this is unstable. than is present to replace them. 4. Resources are limited, therefore only a fraction of offspring survive to reproduce. 5. Survival is correlated with heritable variation. 9 9/11/14 The philosophical content of natural Criticisms and misconceptions selection is scientific 1. Evolution has no • Does not mean that • Is natural selection a • Claim: natural purpose. natural selection is an valid scientific theory? selection is a attack on religion. 2. Evolution has no tautology: • Because it is materialistic, inherent direction. cannot address faith- • Evolution is the 3. Natural Selection is based knowledge. survival of the fittest; materialistic. • Provides explanations • The fittest are those and predictions for the that survive. physical world. Criticisms and misconceptions Criticisms and misconceptions • Argument for natural • Is natural selection a selection takes form: • Is natural selection a • Claim: Natural Selection valid scientific theory? – A statement of facts valid scientific theory? is unscientific because it regarding variation. cannot be disproved. – Can explain everything, – A statement of facts and therefore nothing. regarding population growth and limiting resources. – Logical inferences based on these facts. – If the facts or inferences are incorrect, then theory is false. 10 9/11/14 Criticisms and misconceptions Criticisms and misconceptions • Is natural selection a valid scientific theory? • The argument from design • Testable AND falsifiable questions: • William Paley (1802): “Natural Theology, or – Do individuals vary in their characteristics? Evidences of the Existence and Attributes of the – Does variation have a genetic basis, at least in part? – Is new variation created by copying errors in the duplication of Deity Collected from the Appearances of Nature” DNA in the germ cell line? • Analogy of the watch. – Is new variation random with respect to need? – Do populations have the potential to increase exponentially? • Raised difficult theoretical questions about the – Blending inheritance, no natural selection. nature of the designer. – Very young earth. • Malaria and sickle-cell anemia. – E.g. Lord Kelvin’s estimate of age of earth (scientific hypothesis) vs. Darwin’s theory of the unity of life. • ‘Design’ of respiratory tract. Criticisms and misconceptions Criticisms and misconceptions • The argument from • Arises from confusion between ‘function’ and • The argument from design ‘purpose’. – Tend to