Developing the Theory of Evolution
Evolution is the core theme of biology Nothing in biology makes sense except in the light of evolution Theodosius Dobzhansky
Pre-Darwin Naturalists of the 1700s were pre-occupied with naming new species accepted a limited time scale assumed the fixity of species used newly invented microscopes and telescope to look at embryos and stars recognized that fossils existed of animals unknown in their explorations
Plato (427-347 BC) Stated that variations in plant and animal populations as being imperfect representations of ideal forms Only the perfect forms of organisms were real: idealism, essentialism philosophy
Aristotle (384-322 BC) - Plato s student Believed all living forms could be arranged on a scale of increasing complexity scala naturae (scale of nature), with no vacancies and no means to improve on this ladder of life. species are fixed, permanent, and do not evolve (Stability of Species)
Natural Theology: based on Judeo-Christian culture (old testament) Argued that adaptations in organisms were planned by the creator. - each and every species designed for a particular purpose Forms today s Intelligent design theory
Thomas Malthus published his Essay on the Principles of Population - survival of the fittest shows the tendency of life to multiply faster than its food supply, which leads to a struggle for existence The Economist Malthus explained population growth to Darwin Populations breed rapidly But populations don t grow unchecked (Limiting Factors) Organisms need to breed to maintain their species This with his observations, he could see now how variations could arise within species.
Thinkers of the 19 th Century European colonialism leads to discovery that the number of species is very large. Maybe species can change after all? Although this was discussed in numerous circles, it was contrary to religious teachings and dismissed as heresy.
Georges Cuvier (1769-1832): Founder of Paleontology (the study of fossils) Opposed evolution Thought that boundaries between fossil layers corresponded to catastrophic events such as Noah s flood or droughts Developed the theory of catastrophism
The oldest fossils are in the oldest strata
James Hutton:(1726-1797) Scottish Geologist In 1795 suggested Gradualism - profound change is the cumulative product of a slow but continuous process. He looked at a present day process like erosion by water and believed that these processes operating over millions of years could have created the geologic features we see today.
Charles Lyell (1797-1875): Uniformitarianism An embellishment on Hutton s gradualism, geological processes are so uniform that their rates and effects must balance out through time Suggested the Earth was hundreds of millions of years old. Darwin took only three books with him on the Beagle. One was Lyell s book Principles of Geology
Jean Baptiste Lamarck (1744-1829) - The Inheritance of Acquired Characteristics - environmental pressures require animals to strive (unconsciously) toward higher branching pathways of perfection - Believed that evolution responded to organisms felt needs i.e. use and disuse : examples: biceps of blacksmith, giraffes neck - inheritance of acquired characteristics: modifications acquired during a lifetime can be passed on to offspring - Although wrong, his thinking was visionary. (Environment)
Erasmus Darwin (1731-1802) Charles Darwin s grandfather observed adaptations of all kinds including protective coloration noted intricate web of ecological relationships among different forms of life estimated the antiquity of the earth at millions of ages recognized that through a certain similitude on the features of nature that the whole is one family of one parent believed in acquired heritable characteristics
Natural Selection Charles Darwin (1809-1882) originally intended to study medicine at Edinburgh; later went to Cambridge left to go as a naturalist on the voyage of the Beagle in 1831 to South America Darwin Video
In 1831 he left on a 5 year voyage on board the Beagle to survey the coast of South America. He stopped off at the Galapagos Islands for five weeks where the diversity of the plants and animals amazed him.
Darwin saw variation within species on the different Islands. But didn t fully understand what he saw till he returned to England
Darwin s Finches
Natural Selection Darwin reached England in 1836 met Charles Lyell talked with stock breeders and dabbled in breeding himself read Malthus in October 1838 was a friend of Alfred Russel Wallace (1823-1913) who arrived at the theory of natural selection at the same time presented his views with Wallace before publication of On the Origin of Species
Natural Selection Charles Darwin published On the Origin of Species by Means of Natural Selection on November 24, 1859 It was an overnight best-seller
Comparison of Lamarck s Theory with that of Darwin
Darwin s Theory of Natural Selection All organisms exhibit variability All organisms reproduce more offspring than survive Therefore, it must be that: Those individual variants best fitted to their environments survive Those less well fitted fail to reproduce The characteristics thus favored by selective pressure are passed on to the next generation
The End
Evidence for Evolution Evidence Available to Darwin Fossils Taxonomy Comparative Anatomy Comparative Embryology Biogeography
Fossils Fossils are remains or imprints of past life preserved in sediments occur in layers (strata) many no longer occur others resemble modern species
Strata layers in Rocks
Fossilized remains of a bird like dinosaur Archeopteryx
Fossil trilobite
Fossils in Amber
Fossil Jellyfish
Fossil Evidence for Evolution Fossils distributed consistently throughout strata of same age Order of fossil appearance shows more complex forms appearing after simpler forms Recent fossils (new strata) most closely resemble modern organisms
Evidence for Evolution Evidence Available to Darwin Fossils Taxonomy Comparative Anatomy Comparative Embryology Biogeography
Taxonomy Hierarchical classification structure developed by Linnaeus Implies that species can be grouped together based on their relatedness Bears with bears, bees with other bees A family tree can be made implying descent
Related species of Ursus
Family Tree of Bears
Evidence for Evolution Evidence Available to Darwin Fossils Taxonomy Comparative Anatomy Comparative Embryology Biogeography
Comparative Anatomy Compares anatomical structures from different organisms Similar structures in two or more species are called homologous structures Homologous structures may perform different tasks in different organisms
Homologous forelimbs
Family Tree of the Horse (Equus)
Evidence for Evolution Evidence Available to Darwin Fossils Taxonomy Comparative Anatomy Comparative Embryology Biogeography
Comparative Embryology Embryos (young stage of organisms are compared) Show similar features due to shared ancestry All vertebrates have tails gill-like branchial arches
Evidence for Evolution Evidence Available to Darwin Fossils Taxonomy Comparative Anatomy Comparative Embryology Biogeography
Biogeography Distribution of species Many related species occur across the earth Isolated areas (islands, Australia) often have unique species Biogeography explained by continental drift of plates and speciation
Map of Oceanic Crust Ages in the Atlantic
Map of Earthquake Epicenters, 1980-1990
Molecular Biology Not available to Darwin in 1800 s Includes comparisons of protein sequences DNA sequences cytochrome c chloroplast genomes (plants only) Used to developed phylogenetic trees (hypothesized relationships)