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Home , Carl Linnaeus, On the Origin of Species, Timeline of ornithology

The roots of evolutionary History of Evolutionary Thought thinking

Learning objectives: 2008 will mark the 150th anniversary 1. To describe major historical events and of the reading of addresses on the theory of key contributors to the development of the theory of . evolution by by Wallace and Darwin, but the roots of evolutionary thinking 384-322 BC 2. To outline the key components of Darwin’s are usually traced back to the Greek philosopher theory of evolution by natural selection. Aristotle. Aristotle developed the idea of a natural “Scala Readings: Your text does not cover this topic (except naturae”, in which all forms of were linked in a for box 2.1 and scattered parts of Ch. 2). “chain of being”. However, the people and events mentioned have Aristotle thought of as unchanging and Wikipedia entries. reflecting a divine order. 336-2 1 336-2 2

Carl Linnaeus: father of : father of modern modern taxonomy

Linnaeus is credited with developing the binomial Linnaeus recognized that individuals within a system, in which each species name Linnaeus Linnaeus 1707-1778 species are capable of interbreeding, while 1707-1778 has two parts individuals in different species could not interbreed. name + specific epithet = species name Linnaeus believed in the ‘balance of ’, with each pepo = cultivated pumpkin species having a place in the divine plan. Species do sapiens = modern not change or go extinct. Later in life, Linnaeus acknowledged that new species Linnaeus also saw species as nested within broader could be formed by hybridization (by crossing groups, e.g. families include many genera, genera include many species, etc. different species) 336-2 3 336-2 4 Linnaeus the famous George Louis Leclerc, professor Compte de Buffon

Linnaeus was an interesting and somewhat Buffon was a French mathematician and eccentric man. naturalist who influenced Lamarck and Darwin. Buffon believed that biological diversity could He spent his academic career in at the University of Buffon be accounted for by material processes operating , but as time went on, he spent most of his 1707-1788 time at Hammarby (his summer cottage 16 km outside in nature. He believed the Linnaean reflected , Uppsala). There he taught classes and led walks with change over time. through the surrounding natural areas. His process: new species form when migrate new environments then cause changes to the species

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Erasmus Darwin: organisms Jean-Baptiste Lamarck: a adapt to their environment of evolutionary change

“Organic life beneath the shoreless waves Lamarck was a French naturalist Lamarck Was born and nurs’d in ocean’s pearly caves; E. Darwin He believed that organisms progress from simple 1744-1829 through more complicated forms. Simple forms First forms minute, unseen by spheric glass, 1731-1802 of life were seen as constantly originating Move on the mud, or pierce the watery mass; through These, as successive generations bloom, Lamarck suggested a mechanism (2 ‘laws’)for New powers acquire and larger limbs assume; evolutionary change: Whence countless groups of vegetation spring, 1. Use or disuse of a structure leads to its development or diminishment (within the And breathing realms of fin and feet and wing.” lifespan of an individual) The Temple of Nature (1802) 2. These acquired characters could then be passed on to offspring. 336-2 7 336-2 8 (from , 1809) Thomas Malthus: Principle of : Geologist and Overproduction Supporter of Darwin

Lyell was an English geologist and contemporary of Malthus was an English clergyman, demographer and political Malthus and Alfred Russell Wallace. Both Lyell economist who had a major influence 1766-1834 were heavily influenced by Lyell’s “Principles of 1797-1875 on both Darwin and Wallace. ”. Lyell visited Mount Etna in Sicily. He saw the He wrote an essay on the Principle of Population in 1797: crater had been built up by numerous small • Most organisms (including ) produce more offspring than can possibly survive eruptions, and understood that geological events • Even when resources are plentiful, populations tend to continue were always changing the shape of the Earth. growing until they outstrip their food supply Lyell also observed mollusks, similar to • Once resources become scarce, populations experience a struggle modern species, and in noting the number of layers for existence, in which (for humans) poverty, disease and famine in sedimentary rock, he inferred that the Earth ensue. must be very old.

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Charles Lyell: Geologist and Charles Darwin Supporter of Darwin Darwin was a man of independent means, who was The idea that the Earth was constantly changing, able to devote himself to his passion: . but without progress or development. His father wanted him to be a doctor, then a This idea of constant change, the constant action clergyman, but eventually allowed young Charles to of natural forces (), influenced participate in an expedition as a ship’s naturalist. Darwin many naturalists and was important to the 1809-1882 development of Darwin’s thinking about how the mechanism of evolution might work. The voyage However, Lyall initially thought of the living world of the as created, though he later became a strong Beagle, proponent of evolution (after reading Darwin’s 1831-1836 book).

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The voyage of the Beagle, 1831- , 1831- 1836. 1836.

Many observations Why do lead Darwin to different species pose challenging tend to occur in questions: areas separated Why are Rheas so by boundaries similar to (e.g. oceans)? ?

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e.g. Galapagos finches: a group "When I see these Islands in sight of each other, and of 14 species possessed of but a scanty stock on animals, tenanted by that differ in these , but slightly differing in structure and filling the same place in Nature, I must suspect they are only habitat and food varieties....If there is the slightest foundation for these choice. remarks the of Archipelagoes - will be well worth examining; for such would undermine the stability of Species." (1836) 336-2 15 336-2 16 Work on the Charles Darwin Galapagos finches continues to the Back in Britain, Darwin developed his theory of natural selection. present day - as

you will see in a Darwin recognized several critical facts: few weeks Variability exists within species Variant traits may be inherited (Darwin didn’t know how) through your Malthus’s Principle of Overproduction implies that many individuals must die or fail to reproduce. tutorial reading of Individuals slightly better suited to their environment must be more a paper by P. and likely to survive. Therefore, some variants will be preserved over time more than others. R. Grant. The composition of populations must change over time. !Evolution by natural selection.

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Charles Darwin Alfred Russell Wallace

Darwin on of species Wallace was a working naturalist. In 1858, sent a letter to Darwin describing As natural selection acts his independent discovery of natural on geographically isolated selection. Wallace 1823-1913 populations, they become increasingly different from Like Darwin, Wallace traveled around the world observing each other. This leads to and . Like Darwin, he’d read Lyell the formation of first and Malthus, and eventually realized that: varieties within a species, “[the] self-acting process [of natural selection] would then separate species, necessarily improve the , because in every generation then genera, etc., in an the inferior would inevitably be killed off and the superior ever-branching process. would remain - that is, the fittest would survive.”

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Charles Lyell and Joseph Hooker quickly arranged for 1. Populations change over time = evolution happens. Darwin's and Wallace's views to be co-presented at the meetings of the Linnaean Society in London in 1858. 2. All species are related through common ancestry = the connects living and extinct species. The next year (1859), Darwin published The Origin of Species by Means of Natural Selection. The depth and 3. Evolution happens through the action of natural breadth of Darwin's book, developed over twenty years of selection. thought and research, revolutionized .

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Darwin the man

Darwin continued to work on • Austrian scientists and a Catholic (Augustinian) natural history and evolution priest, born near Vienna in July 1822 (died 1884). in groups from pigeons to • Educated in physics and math at the University of Vienna • Lived and worked in Brno, at the abbey of St. Thomas. orchids. He wrote many • Studied patterns of inheritance using garden and books and articles. other . • Was a contemporary of Charles Darwin (1809-1882). He shunned the public eye • The significance of Mendel’s work was not recognized by and continued to work the scientific community until after his and the quietly on his estate outside rediscovery of his work in 1900 by Correns and DeVries. London until his death in 1882, at the age of 73. 336-2 23 336-2 24 Mendel’s Experimental System: Mendel’s unique contributions Garden peas, Pisum sativum

Annual plants, easy to grow, • The study of large numbers of progeny (allows capable of self-fertilizing and the effects of chance to be minimized). cross-fertilizing, variable in a • The use of more than one generation of crosses number of traits. to understand patterns. • The use of reciprocal crosses to see if the sex Mendel’s experiments yielded of the parent affects patterns of inheritance. the principles of inheritance: • The use of test crosses to determine the Segregation, and independent genotype of a parent in a cross. assortment.

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Linking Mendelian and When traits don’t behave Meiosis according to Mendel’s laws

Mendel’s work was not appreciated until its rediscovery in 1900. Three years later, in • Mendel’s studies focused on traits with relatively simple 1903, Sutton and Boveri linked Mendel’s patterns of inheritance. This was critical to establishing results to the behaviour of in the fundamental rules of . meiosis, formulating the theory • There are many other traits that could have been of inheritance. measured on Mendel’s plants. Some of these would not have yielded clearly interpretable patterns. • For example, leaf length, total mass, number of on the stems... These traits don’t fall into clear categories. Instead they show continuous variation and are called quantitative traits. 336-2 27 336-2 28 Sir (1890-1962): Linking quantitative traits Conclusions variation and mendelian genetics • Scientific inquiry occurs in a particular • In 1918, Fisher showed that a large number of Mendelian social/ historical context. The formulation factors (genes) influencing a trait would cause a nearly of the theory of evolution by natural continuous distribution of trait values. Therefore, mendelian genetics can lead to an approximately normal distribution selection by Darwin and Wallace represented a natural progression from the ideas and foundations of their predecessors.

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