Aristotle. Carolus Linnaeus. Carolus Linnaeus. Carolus Linnaeus. Greek philosopher. Examined natural world for evidence of divine order

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1 Greek philosopher Scala naturae ( Chain of Being ) Hierarchical arrangement of forms Species arranged linearly along a scale: God ManMammals Aristotle BC Examined natural world for evidence of divine order Egg-laying animals Insects PlantsNon-living matter Formed the basis for the western belief in a fixity of species, each of which has a typical form Carolus Linnaeus AD The father of modern taxonomy Classified organisms according to a binomial system, giving each a specific and a generic name, e.g. Homo sapiens Genus species Proposed a nested system of relationships (as opposed to the Scala naturae) Carolus Linnaeus AD The father of modern taxonomy The modernized Linnaean system groups organisms into: Kingdom Phylum Class Order Family Genus Species Humans Animalia Chordata Mammalia Primates Hominidae Homo sapiens Carolus Linnaeus AD The father of modern taxonomy Recognized fundamental difference between interbreeding organisms (within a species) non-interbreeding organisms (different species) Believed in balance of nature Each species has its place in a divine plan Species would not change or go extinct Eventually acknowledged limited formation of new species by hybridization

2 Comte de Buffon AD Dégéneration Believed that the origin of life & species followed material processes Looked for evidence in the physical & biological world Believed Linnean hierarchy reflected common descent (dégéneration), with divergence over time. Physical environment (somehow) changes organic particles New species form when animals migrate New environment then causes change to the species Change only happen within families: each family conforms to an internal mold. Species can change over time but are limited to their original mold. Erasmus Darwin AD Grandfather British philosopher, naturalist & physician Wrote Zoonomia: Or The Laws of Organic Life Believed organisms constantly attempted to improve themselves by adapting to their environment Transformism or transmutation All of life consists of one living filament connecting all living forms to a common ancestor Erasmus Darwin AD Organic life beneath the shoreless waves Was born and nurs d in ocean s pearly caves; First forms minute, unseen by spheric glass, Move on the mud, or pierce the watery mass; These, as successive generations bloom, New powers acquire and larger limbs assume; Whence countless groups of vegetation spring, And breathing realms of fin and feet and wing. The Temple of Nature (1802) No real mechanism for this transformism Jean-Baptiste Lamarck AD Inheritance of acquired characters French professional naturalist Theory of transformism! Organisms progress through a hierarchy of ever-moreadvanced forms (Scala naturae in reverse?) "Nature, in producing in succession every species of animal, and beginning with the least perfect or simplest to end her work with the most perfect, has gradually complicated their structure."! At the base of this hierarchy, simple organisms constantly arise by spontaneous generation

3 Jean-Baptiste Lamarck AD Inheritance of acquired characters Suggested a mechanism for this organic progression in Philosophie zoologique (1809): First law: Use or disuse of a structure leads to its development or diminishment Second law: These acquired characters can be passed on to offspring Principle of overproduction English clergyman Thomas Malthus AD Major influence on Darwin & Wallace An Essay on the Principle of Population (1797) Most organisms produce far more offspring than can possibly survive Even when resources are plentiful, populations tend to grow geometrically until they outstrip their food supply Poverty, disease, and famine are inevitable, leading to a struggle for existence. English geologist Charles Lyell AD Uniformitarianism His Principles of Geology was a major influence on Darwin & Wallace Believed earth is constantly changing Processes that molded earth s surface can be understood by modern-day events Uniformitarianism: earth is subject to gradual, continuous change But without progress or development Earth remains at a steady state Charles Lyell AD Uniformitarianism Lyell applied his views to the living world. Initially he believed that some members of all classes of organisms existed throughout the history of the earth. What had changed was the abundance and location of species as well as the exact form of each species. [S]pecies have a real existence in nature, and that each was endowed, at the time of its creation, with the attributes and organization by which it is now distinguished.

4 The Voyage of the Beagle ( ) The Man An English gentleman of private means Was able to focus on his life s work: the development of the theory of evolution by natural selection Read Lyell s Principles of Geology while on board (and correctly applied the principle of uniformitarianism to the formation of coral reefs) Developed an appreciation of biogeographical patterns Biogeography on the Beagle Noticed that two similar species often coexisted in a boundary zone neither one better adapted than the other These species must compete with each other Rheas - a flightless South American bird Rhea americana (common rhea) Pterocnemia pennata (Darwin s rhea) Biogeography on the Beagle Why do different groups of organisms live in areas separated by barriers (like the ocean)? Why are the rhea and the ostrich so different, even though they have similar lifestyles under similar circumstances? Would a creator be limited by boundaries to migration?

5 Biogeography on the Beagle Why do different groups of organisms live in areas separated by barriers (like the ocean)? Biogeography on the Beagle Why do different groups of organisms live in areas separated by barriers (like the ocean)? On the Galapagos Islands, Darwin was told that even islands that were very close together had giant tortoises that were distinct from one another Dr. Robert Rothman "When I see these Islands in sight of each other, and possessed of but a scanty stock on animals, tenanted by these birds, but slightly differing in structure and filling the same place in Nature, I must suspect they are only varieties...if there is the slightest foundation for these remarks the zoology of Archipelagoes - will be well worth examining; for such facts would undermine the stability of Species." (1836)

6 Back in Britain: The theory of natural selection Darwin recognized several critical facts: Variability exists within species Variant traits may be inherited (Darwin didn t know how) Malthus s Principle of Overproduction implies that many individuals must die or fail to reproduce Individuals slightly better suited to their environment must be more likely to survive Therefore, some variants will be preserved over time more than others. The composition of populations must change over time!evolution by natural selection. The origin of species As natural selection acts on geographically isolated populations, they become increasingly different from each other This leads to the formation of first varieties within a species, then separate species, then genera, etc., in an everbranching process. Alfred R. Wallace AD Evolution made public Natural selection co-discovered English professional naturalist In 1858, sent a letter to Darwin describing his independent discovery of natural selection Like Darwin, travelled around the world observing biodiversity and biogeography Like Darwin, he d read Lyell and Malthus, and eventually realized that [the] self-acting process [of natural selection] 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. Charles Lyell and Joseph Hooker quickly arranged for Darwin's and Wallace's views to be co-presented at the meetings of the Linnean Society in London in The next year, Darwin published The Origin of Species by Means of Natural Selection. The depth and breadth of Darwin's book, developed over twenty years of thought and research, revolutionized science.

7 Gregor Mendel AD Mendelian genetics The greatest weakness of the theory of natural selection was lack of knowledge of how inheritance worked Mendel s work (re-discovered in 1900 by Carl Correns & Hugo de Vries) clarified the laws of inheritance (at least for discrete traits like pea color) Gregor Mendel AD Mendelian genetics The greatest weakness of the theory of natural selection was lack of knowledge of how inheritance worked Mendel s rules explain why offspring tend to resemble their parents. Show that variation is not lost over time due to reproduction alone Still unclear whether these rules apply to continuously varying traits (height, weight, etc.) R. A. Fisher AD Image credits Uniting Mendelian and quantitative genetics In 1918, Fisher showed that a large number of Mendelian factors (genes) influencing a trait would cause a nearly continuous distribution of trait values Mendelian genetics can lead to an approximately normal distribution Aristotle: admissions/text/process.html Linnaeus: Buffon: Erasmus Darwin: science.ntu.ac.uk/erasmus.html Lamarck: Malthus: homepages.caverock.net.nz/~kh/bobperson.html Lyell: athene.as.arizona.edu/~lclose/teaching/nats102/lyell.gif : Beagle map: Rhea: Ostrich: Finches: Tortoise: Wallace: Mendel: Correns: de Vries: Fisher:

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