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Ch. 14 Principles of Evolution. What is a species?. There really isn’t a good definition for species, so we need to come up with a working one. A species is a group of organisms whose offspring can interbreed. Evolution of Evolutionary Thought.
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What is a species? • There really isn’t a good definition for species, so we need to come up with a working one. • A species is a group of organisms whose offspring can interbreed.
Evolution of Evolutionary Thought • Original thought was that all organisms were created simultaneously by God and that they remain fixed and unchanging from the moment of creation. • This idea was expressed by many ancient Greek philosophers.
Evolution of Evolutionary Thought • Plato (427-347 B.C.) • Proposed that each object on Earth was merely a temporary reflection of its divinely inspired “ideal form” • Aristotle (384-322 BC) • Categorized all organisms into a linear hierarchy that he called the “ladder of Nature”
Evolution of Evolutionary Thought • The ideas of Plato and Aristotle provided the basis for unchanging organism. • This view reigned unchallenged for nearly 2000 years.
Evolution of Evolutionary Thought • Until the 1700’s, Creationism was the accepted theory. • 1) Each species was created individually by God. • 2) Earth was the center of the universe. • 3) Man stood as the pinnacle of creation.
Georges Louis LeClerc, “Buffon” (1707 – 1788) • Suggested that the original Creatoin resulted in a relatively small number of founding species, and that some modern species had evolved through natural processes.
William Smith (1769 – 1839) • Surveyor, noticed that certain fossils were always found in the same layers of rock. • He also noticed that fossils and rock layers were in a consistent organization: Younger fossils/rocks near the surface, older fossils/rocks deeper.
Georges Cuvier (1769 – 1832) • Cuvier proposed the theory of Catastrophism. • Hypothesized that a vast supply of species was created initially. Successive catastrophes (Ex. Great Flood) produced layers of rock and destroyed many species, fossilizing some of their remains. • Modern organisms were ones that survived
James Hutton (1726 -1797) & Charles Lyell (1797-1875) • Developed uniformitarianism • Contemplated the forces of wind, water, earthquakes, and volcanism. • Said the layers of sediment normally drit to the bottoms of rivers and lakes • Slow, natural processes alone produced layers of rock thousands of feet thick. • Therefore, the Earth must be old.
Jean Baptiste Lamarck (1744 – 1829) • 1st to propose a mechanism for evolution “Inheritance of Acquired Characteristics” • The bodies of living organisms are modified through the use or disuse of different parts. • Modifications are then inherited by offspring. • Why modification? • Stated that all organisms have an inherant drive for perfection.
Lamarck Example • Ancestral giraffes tried to gain access to additional food by stretching upward to feed on leaves. • This resulted in their necks becoming slightly longer. Their offspring would inherit these longer necks, then stretch their own necks farther, etc., etc., until we get our modern giraffes.
Lamarck • Lamarck’s mechanism does not work. • We know that acquired characteristics are not passed to offspring. (Ex. Scars) • Lifting weights doesn’t make your children have larger muscles, dying your hair doesn’t give your children the new hair color.
Alfred Wallace (1823-1913) • Came to the same conclusion as Darwin. • Presented/Described the same mechanism for evolution in similar papers that were presented to the Linnaean Society in London in 1858.
Charles Darwin (1809-1882) • Developed the Theory of Evolution and proposed a mechanism for how it worked. • Darwin published his book On the Origin of Speciesby Means of Natural Selection in 1859. • Life’s varitey arose through descent with modification
Natural Selection • Observation 1: A natural population, has the potential to grow rapidly because organisms produce far more offspring than are required to replace themselves. • Observation 2: The number of individuals in a population tends to remain relatively constant.
Natural Selection • Conclusion 1: More organisms must be born than survive. Organisms compete to survive and reproduce. • Observation 3: Individuals differ from one another in many respects, including ability to obtain resources, withstand environmental extremes, and escape predators.
Natural Selection • Conclusion 2: These differences help determine which individuals survive and reproduce. This process, by which those individuals whose traits are most advantageous leave a larger number of offspring, is known as natural selection.
Natural Selection • Observation 4: At least some of the variation in traits that affect survival and reproduction is due to differences that may be passed from parent to offspring. • Conclusion 3: Individuals that are best suited to their environment leave more offspring, the traits are passed to a larger proportion of the individuals in the next generations.
Evidence For Evolution • Fossils • Comparative Anatomy • Comparative Embryology • Molecular Biology
Fossils • Transitional forms of animals show forms of evolutionary change. • We can see changes that have occurred over time. • Can connect modern species with past organisms.
Comparative Anatomy • Comparing similarities between the structures of organisms. • 3 types of structures • Homologous Structures • Analogous Structures • Vestigial Structures
Homologous Structures • Structures that are internally similar, but differ in their function. • Example: Human arm, Dog forarm, Dolphin fin, Bat Wing • Homologous structures show divergent evolution. Organisms shared a common ancestor, hence the similarities in the structures.
Analagous Structures • These are structures that perform the same function and look the same, but internally are different. • Ex. Whale fin, Penguin Wing, Shark Fin • These structures show Convergent Evolution. Selective pressures from the environment have brought about similarities in the structures.
Vestigial Structures • These are structures that are present in an organism but no longer have a use. These structures are also normally found in related organisms and are useful. • Ex. Pelvic bones in whales and certain snakes (have no legs, therefore they do not need pelvic bones). Molar teeth in Vampire Bats.
Comparative Embryology • The study of looking at how embryos of different species develop and looking at the similarities between them. • Ex. Gill slits develop in human embryos as well as many other embryos. • Comparative embryology helps to show that two organisms shared a common ancestor.
Molecular Biology • Looking at the nucleotide sequence of DNA or the amino acid sequences of protein. • The more alike the sequences are, the more closely related the two organisms. The less alike they are, the less closely related the two organisms are.
