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Charles Darwin, Alfred Wallace, and Natural Selection Charles 8/29/2011 Charles Robert Darwin (1809-1882) Charles Darwin, Alfred Wallace, and Natural Selection 1881 1840 Charles Darwin by the early 1800s: •credited with “discovering” evolution • Generally accepted that both plants and • On the Origin of Species animals are sexual organisms • did two things • males use sperm/pollen to pass traits; females •established that species have changed over time use eggs (evolved) • need for pollen in sexual reproduction by •proposed a mechanism for how that process took plants is well known place (natural selection) 1. Stable varieties nearly always breed true. 2. You can mate two different parents to Also by the early 1800s, farmers and generate hybrids, which can be identical to stockbreeders had some “rules of one parent or combine features of both parents. (hybrid x hybrid crosses result in thumb” on practical genetics. extreme variation in the offspring → hybrids don’t breed true) 3. Sometimes you get “sports” (mutants), even in stable varieties. (The sports could be backcrossed with “normals” to create new stable varieties.) 1 8/29/2011 • Erasmus Darwin: wrote a book ( Zoonomia ) and poems that included passages about But, a prevalent idea in the 19th century was organisms changing over time fixity of species • Buffon (Laclerc): in his 44 volume magnum – each species is a separate creation by a creator opus, provided evidence for change over time – species have not changed over time • Lamarck: hereditary change over time occurred due to characteristics acquired That species are not fixed: “a common enough during the lifetime of an organism heresy at the time” • striving to acquire a trait vs. the random occurrence of mutations Disproving Lamarck Natural Selection • Remember: science as a process to acquire mid-1800s: information to understand the natural world Alfred Russel Wallace and Charles Darwin • based on observations, formulate hypotheses, make independently proposed that inherited change predictions, do experiments over time occurs by natural selection • If Lamarck is correct, then we should be able to alter an existing trait and then see that new version passed to offspring • Removed mouse tails for several generations. Tails never disappeared from subsequent generations; tails didn't even get shorter over time. Alfred Russel Wallace Charles Robert Darwin • 1855: "On the Law Which Has Regulated the Introduction of New Species" • 1859: On the Origin of Species – – In this pre-natural selection essay Wallace all provided copious evidence that species are not fixed but directly states the role of natural – proposed theory of natural selection selection in an evolutionary interpretation of as the mechanism for evolutionary geographical and geological patterns of change species distribution. • 1868: Variations in Animals and • 1858: "On the Tendency of Varieties to Plants under Domestication – used domestication of species to Depart Indefinitely from the Original show how selection of certain traits Type" over time can change a species – The 'Ternate essay' Wallace sent to Darwin containing the former's original elucidation of the theory of natural selection. 1868 Portrait by Julia Cameron http://kentsimmons.uwinnipeg.ca/16cm05/1116/16evolut.htm http://people.wku.edu/charles.smith/index1.htm http://www.mtholyoke.edu/courses/awlee/art242/cameron/image3.html 2 8/29/2011 • They were two of the many Europeans who went to New World tropics in the 19 th century as naturalists • Darwin was on an official survey mission with the British Navy; originally as the captain's social companion; became the de facto naturalist • Wallace went with a friend (Henry Walter Bates); backed by a vendor in Britain who would sell their collections • Both Darwin and Wallace collected multiple • Both shared the two sources of information individuals of the same species – saw the for their eureka moment variation of a single species • 1. observing biogeography of similar species • saw similarities between species in adjacent on nearby islands locales • Darwin, the Galapagos Islands • observed geographic distributions of species • Wallace, the Malay archipelago (biogeography) Natural Selection • 2. Read Malthus • resources limit the numbers in a population • more offspring are produced than can survive • the human population will outstrip its food supply • individuals within a population vary; at least unless the population is held in check by war, some of the variation can be inherited disease, etc. • differential reproduction and survival • Darwin and Wallace realized that natural • populations are held in check by some limiting therefore, over time, the most advantageous factor in their environments; only those traits for reproduction and survival individuals that survived the “check” will (adaptations) will increase in a population reproduce 3 8/29/2011 Adaptation Darwin in the Galapagos • structure, physiology, behavior • was collecting tortoises • aids in fitting an organism to its environment • someone told him that he must • examples have been on island X in order to get those tortoises – the butterfly egg mimics on the passionflower • Darwin realizes that the different tendrils islands have distinct species and – creosote bush produces that he should label his collections as coming from a allelopathic chemicals specific island, rather than the which reduce competition Galapagos as a whole. for water and minerals • has to re-label his bird collections http://www.tarleton.edu/Departments/range/Shrublands/Sonoran%20Desert/sonorandesert.html Darwin's Finches http://cas.bellarmine.edu/tietjen/Ec&Ev_Distance_learning/Finches/darwin_review.htm C. Darwin, On the Origin of Species Darwin's Orchid Natural Selection • result of variation, differential reproduction, and heredity • it is not planned; there are no goals; there is no "progress" up an evolutionary ladder • it does not produce perfection; an organism is “good enough” to survive long enough and produce offspring Angraecum sesquipedale Xanthopan morganii praedicta http://www.larsen-twins.dk/orch-new/Orc_a/Angraecum_sesquipedale_391-22x.html http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/t045/T045107A.jpg 4.
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