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Biol 4974/5974 Evolution as a concept 8/22/2013 Evolution as a Concept Learning goals Understand how the meaning of “evolution” itself and how it has changed over the last two centuries. The factors that led to these changes. Evolution as a “theory” and what that means. How evolution can be studied using the scientific method. “Universal properties” among organisms • Same mechanism of inheritance; same genetic code in DNA. • Bodies built of cells. • Living organisms reflect the sum of inherited changes over “billions of years of existence on earth.” 1 Biol 4974/5974 Evolution as a concept 8/22/2013 What do we mean by evolution? Based on Latin term evolutio. Meaning? • Used to describe the development of an organism. • Tracked to 18 century view: “preformation.” e.g, butterfly coming out of a chrysalis e.g., pea aphid (asexual)—multiple generations of embryos p. 5. Common definitions of evolution (see text p. 4): 1. “The process by which different living organisms are thought to have developed or diversified during the history of the earth.” 2. The gradual development of something , from a simple to a more complex form. For example, a concept or language. 3. “A pattern of movements or manuevers.” 4. “Chemistry—giving off a gaseous product.” Merriam Webster online • • • • • • • • • • • • • • • : one of a set of prescribed movements 2 a: a process of change in a certain direction : unfolding b: the action or an instance of forming and giving something off : emission c (1): a process of continuous change from a lower, simpler, or worse to a higher, more complex, or better state : growth (2): a process of gradual and relatively peaceful social, political, and economic advance d: something evolved 3 : the process of working out or developing 4 a: the historical development of a biological group (as a race or species) : phylogeny b: a theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations; also: the process described by this theory 5 : the extraction of a mathematical root 6 : a process in which the whole universe is a progression of interrelated phenomena Older views • Spontaneous generation: small organisms P. 7 Johann van Helmont Box 1.1, p. 8—countered experimentally by Francesco Redi • Fixation of species (Great Chain of Being) from Aristotle on. Species constancy. Challenges: • Fossil discoveries coming to light, late 18th century and lots in 19th century. 2 Biol 4974/5974 Evolution as a concept 8/22/2013 Darwin and Wallace • Together presented a mechanism, Natural Selection, that could connect all organisms • “A single tree of life.” • 1859, On the Origin of Species Defined the study of evolution as: • “The origin and transformation of species. • “The transformation of major groups or lineages of organisms and the search for their ancestors. • “The transformation of physical features, such as jaws, limbs, kidneys, and nervous systems within lineages of organisms.” Natural selection provided the mechanism for these changes. Modern synthesis • Natural selection was a challenge to accept until Mendelian genetics was understood. • Side-tracked by the implications of mutation. • Mutation implied major evolutionary jumps (saltations) rather than gradual change. • Countered with Hardy-Weinberg “equilibrium,” which detected natural selection at work. • RA Fisher’s models of Mendelian inheritance. Evolution is hierarchical • Genotype level • Organismal level • Population level • Need to understand all the levels to understand how evolution works and the effects over time. 3 Biol 4974/5974 Evolution as a concept 8/22/2013 Why is evolution a “theory”? • Is that a criticism? • What is a theory in science? Can we use the scientific method to study evolution? • How can we study something we cannot see? (what about gravity, atoms, the theory of relativity? Can we see these?) • See P. 13 and Box 1.1 For example, we can test evolutionary ideas by • Generating hypotheses tested by examining the fossil record. • Generate hypotheses testing by comparing different organisms or constructing relationships. • Test hypotheses by conducting experiments (e.g., Box 1.3) 4