Outline. Evolution: Evidence, Selection and Adaptation. Key Concepts: One of the key words of our modern time is Evolution

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1 Evolution: Evidence, Selection and Adaptation One of the key words of our modern time is Evolution u 1. Key concepts Outline u 2. Early Beliefs, and New Discoveries u 3. Darwin developed the theory of evolution u based on his observations and other evidence a. Darwin s observations b. Factors that influenced Darwin s thinking u 4. Natural selection: A mechanism of evolution u 5. Conclusions Key Concepts: Evolutionary theories gave early scholars new ways to interpret the occurrences in the world Today, biological evolution is interpreted as heritable changes Darwin and Wallace explained evolution on the basis of Natural Selection The traits that characterize a population can change over time

2 Early Beliefs, and New Discoveries Aristotle believed that each kind of organism was distinct from all the rest Chain of Being - fourteenth century (A chain of Being was seen to extend from the lowest forms of life to humans. Biogeography until the fifteenth century, naturalists were not aware that the world is much bigger than Europe, a few scholars began to examine the world distribution of organisms Comparative Anatomy eighteenth Fossils from the late 1600s on geologists added to the growing confusion. Chain of Being (1579) A Flurry of New Theories Lamarck Theory of Inheritance of Acquired Characteristic Darwin Voyage of the Beagle

3 Lamarck s Theories According to Lamarck's theory, life created long ago in a simple state gradually improved. For example, the ancestor of giraffes could have been a short-necked animal. Pressed by the need to find food, the animal stretched its neck, which permanently lengthened. This acquired characteristic (a long neck) was then passed on to the giraffe's offspring. Lamarck inferred, correctly, that environment is a factor in evolution. Lamarck s Theories Charles Darwin [ ] called evolution Descent with modification

4 Darwin s s Voyage At age 22, Charles Darwin began a five-year, round-the-world voyage aboard the Beagle He collected and examined the species that inhabited the regions the ship visited EQUATOR Galapagos Islands Darwin s s observations Prevailing ideas about species: they did not change or interbreed Darwin s evidence for change came from: 1. his observations of living organisms 2. geologic evidence and fossil record 3. theories of population growth Darwin s s observations What the evidence showed: Relationship between living and fossil organisms (distinct yet similar) Among living organisms: distinct yet similar organisms occur in Similar climates S. Africa, Chile, Australia Isolated populations of same species species often change slightly due to geographical isolation Island v. mainland populations Island species often resembles to mainland species

5 Darwin s s Theory Takes Form Armadillo 10 pounds Glyptodont fossil from S. A. (2 tons!) Three Species Native to Three Geographic Realms Rhea of S. America Ostrich of Africa Emu of Australia Darwin s s Theory Takes Form Variations in traits Survival Reproduction Four finch species from the Galapagos Islands

6 Galapagos Islands today Factors that influenced Darwin s s thinking Geology: as Earth changed, so did types of fossil organisms in rock strata Population studies: many organisms are produced; only a few survive to reproduce [Thomas Malthus ( ) Essay on Disease, Famine, and Population Size] Artificial breeding experiments: humans select desirable traits in plants and animals; so does nature Natural selection: A mechanism of evolution Darwin s explanation for species diversity: Nature selects organisms which have inheritable traits (adaptations) suited to their environment which allow them to survive to reproductive age Survivors then breed and pass on these characteristics to their offspring

7 Variation in a Snail Species Shell color and banding patterns differ due to different alleles for the genes for that trait Adaptation and Natural Selection Mutation (Lethal mutation, Neutral mutation, Good mutation) no purpose, no direction Fitness Adaptation to the environment Natural Selection Result of differences in survival and reproduction among individuals that differ in heritable traits An example of natural selection: Darwin s s finches Showed relatively rapid evolution: Ancestral finches from mainland reached islands, underwent adaptive radiation and populated many diverse habitats Ancestral species became groups of closely related yet diverse populations

8 An example of natural selection: Darwin s s finches Natural Selection Selection can increase the frequency of a trait in a population Environment may favor a trait over another Alfred Wallace Developed same theory as Darwin Origin of Species Darwin Evidence for the Theory of Evolution In Conclusion The Theory of Evolution by Natural Selection states More offspring are produces than the environment can support Variant forms of a trait may be more or less adaptive under environmental conditions An adaptive trait allowed organisms to survive and reproduce more frequently. The frequency of that adaptive trait increases in a population

9 In Conclusion Comparative anatomy, biogeography, fossils, and a lot of other evidence showed changes in lines of descent Natural Selection results in modification of traits and can bring about the evolution of a new species