History of Evolution

Slide 1: History of Evolutionary Theory Anaximander to Austrian Monks

Slide 2: The Evolutionary Model  Evolution is based on two models of population change  Mutation—Change In DNA Structure—involves the creation of new life forms  Natural selection involves environmental pressures that favor, restrict, or eliminate life forms  Other factors may favor population change: gene flow (migration) or genetic drift (changes as the product of chance

Slide 3: Overview of Evolutionary Change  First, we look at the history of evolutionary thought from the Greek philosophers to the Darwinist model  Then we look at the mechanisms of evolutionary change  Biological, Molecular, and Population Genetics  Natural Selection  Other Mechanisms of Population Change  Speciation and Taxonomy

Slide 4: Overview of Evolution of Evolutionary Thought  History of Evolutionary Concepts  Greek Precursors  17th Century Theologians  18th Century Catastrophists  18th Century Uniformitarians  Uniformitarianism of Hutton and Lyell  Darwin and Wallace  Gregor Mandel  Key concepts in evolutionary history  Essentialism/Chain of Being  Natural Selection/Mutation

Slide 5: Early Theorists: The Classical Greeks  Anaximander: (6th Century BC)  Argued that men arose from fishes, setting the stage of  He relied on reasoning, not supernatural explanations  Plato and Aristotle: Set the stage for two models of existence  Essentialism, or the ideal type of biological lifeforms  Great Chain of Being, which placed all lifeforms in a hierarchical system of existence from lowest to highest.

Slide 6: Early Models: Essentialism  Essentialism: The ideal reality against which the perceived reality is com pared and contrasted  Plato (above) was the first to come up with the ideal entity (including the human), against which the perceived entity was compared  Aristotle (below) also accepted the idea of a perfect universe, but did not accept the dichotomy that Plato posited. Rather, he saw the essential as the properties of each lifeform and other entities.  Greek gods and goddesses represented the ideal human male and female forms, as reflected in sculpture and other representational art.  Any deviation from the essential reflected some defect in any lifeform, animal or plant.

Slide 7: Early Models: The Great Chain of Being  A hierarchy of entities from the simplest to most complex anticipated the later rise of taxonomy; Karl von Linné (discussed below) drew on this model.  In this view, the human race was the most complex and perfect of all living forms  Humans, however, were below the divine beings (including demons in the model depicted here.

Slide 8: Catastrophism  Earth’s history is product of sudden change  Example: Creation of Earth in six days (upper left), including Adam  Example: Flood (Noah’s Ark), which eliminated all life except Noah’s family and the male and female animals he allowed into the ark  Catastrophism does have some basis of reality: an asteroid that struck the earth 65 million years ago (lower left) nearly destroyed all life

Slide 9: Early Theorists: 17th Century Catastrophists  James Ussher (1581-1656): Argued that humankind created noon, Oct. 23, 4004;(Upper left)  He based his calculations on biblical history and astronomy  Nicholas Steno (1638-1686):  Stratigraphy—sediments deposited by water in a sequence  Robert Hooke (1635-1703)  Described fossils (mineralized remains of lifeforms)  Recognized them as of extinct or early formative creatures  He also described the cell as the basic unit of life and invented the microscope  Adaptation: creatures changed as earth changed  All three explained history of earth as a catastrophic creation.

Slide 10: Early Theorists: 18th Century Catastrophists  Carolus Linnaeus (Carl Linné; 1707-1778)  Inventor of taxonomy—classification of lifeforms based on similarities and differences (Sample taxonomy next slide)  Viewed system as divinely ordained  He also classified human races as being of separate species with their own personality traits  Georges Cuvier (1769-1832)  Developed the science of comparative anatomy  Compared the Anatomy of present lifeforms with those of the fossils forms  Catastrophism: He concluded that the lifeforms of the world changed but they did not evolve

Slide 11: Carolus Linnaeus (Linné)

Slide 12: Early Theorists: 18th Century Uniformitarians  Uniformitarianism: Processes occur at same rate through time—present and past  Georges-Louis Leclerc (Comte de Buffon; 1707- 1788)  He observed that the tides and currents of seas are uniform through time  He concluded that the earth had to be older than 6000 years  James Hutton (1726-1797): Discovered uniformity in 3 processes:  Deposit of strata under oceans  Uplifting seabeds to above sea level by volcanic action  Land erosion by water, wind, and decay  He too concluded that the earth had to be older than 6000 years

Slide 13: Uniformitarianism According to Charles Lyell  Charles Lyell (1797-1875)  Espoused extreme form of uniformitarianism by denying catastrophism (Principles of Geology)  Three aspects hold up today  Geological processes of past are the same as today  Stratigraphy serves to reconstruct history of the earth  Immense amount of time necessary for geological processes to effect change in the landscape  Age of earth: The current estimate is 4.5 billion years

Slide 14: Counterevidence to Lyell’s Model  Five global catastrophes are known to have occurred.  Example: collision of asteroid with earth 65 m.y.a. wiped out 75% of world’s marine species)  Mississippi Delta is less than 100,000 years old—and has been shrinking since 3400 BCE

Slide 15: Evolutionary Theories: Acquired Characteristics  Jean-Baptiste de Lamarck (1744-1829)  Traits acquired in organism’s lifetime  Acquired Characteristics:  Are passed down to offspring  Product of adaptation to changing environment  Progress from simple to complex organisms  Example: elongation of giraffes’ necks to get at leaves of taller trees  Shortcoming:  No example to support theory; natural selection coupled with mutation better explain the lengthening of giraffes’ necks  Counterexamples abound; for example, generations of docking sheep' ’ tails in rural s Spain did not eliminate them.

Slide 16: Evolutionary Theories: Natural Selection  Natural selection Defined:  Evolutionary change by  Differential reproductive success of individuals  within a species (group of organism able to reproduce fertile offspring)  Through successful adaptation to an environment

Slide 17: Charles Darwin (1809-1882) Origin of Species  Charles Darwin (above) observed that pigeons, dogs, and horses were subjected to artificial selection in order to improve their breeding  On Galapagos Islands in 1832, Darwin observed that 14 species of finches adapted in different niches descented from a common ancestor (next slide)  He conceived the idea of natural selection and after years of dithering finally published his conclusions in The Origin of Species in 1859  Alfred Russel Wallace (below) drew the same conclusions—but Darwin published the results first  (Wallace made a bad career move: he sent his results to Darwin asking for comments. Oops!)

Slide 18: Charles Darwin and Natural Selection

Slide 19: Natural Selection: Definition and Implications  Variations are already present when selection occurs  Natural selection has no particular direction— change is random  Therefore, not all evolution is from the simple to the complex  Species can and do become extinct  New species can and do arise (Darwin had no way of explaining how the originated, however.)  Reproductive isolation makes for new species  New species fill new niches, as the finches showed  Thus, dark-winged moths filled a new environment in a soot-darkened coal-fired steel city; birds did not pick them off  The dark colored pepper moth is to the lower part of the photo

Slide 20: Evolutionary Theories: Genetics  It was up to the Austrian monk Gregor Mendel to discover the principle that would lead to the explanation how species originated.  He experimented with peas in monastery garden  In so doing, he found that smooth and wrinkled peas when combined produced offspring resembling their parents  Nothing but smooth peas appeared in generation 2  A ratio of 3 smooth peas to one wrinkled pea appeared in generation 3  The experiments provided the hereditary foundation for “origin” of species: mutation or genetic change

Slide 21: Gregor Mendel and Genetics  Mendel experimented with six other traits: color of peas, texture of pea pods, color of flowers  He found the same outcomes over three generations  The traits were each determined by variants (alleles) of a pair of genes.  Mendelian traits were thereby discovered  Later, it would be discovered that multiple genes could determine a single trait, such as eye and skin color

Slide 22: Molecular Genetics  The final step to understanding origins of species came with the discovery by James Watson (left) and Francis Crick (right) of a double helix molecule that determine traits of all species  Called DNA, they found that mutations could change the traits of a species—any species of a plant or animal.  Details of this process are discussed in the next set of slides.

Slide 23: Conclusion  Trends in history of evolutionary thought have been reviewed  Creationism to evolutionary models of change  Catastrophism to uniformitarianism  Essentialism to natural selection  Chain of being to variation by random mutation  Evidence fits evolutionary change better than model of creation  How evolutionary change occurs is covered in the next sets of slides.