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Chapter 22

Chapter 22 . Descent with Modification: A Darwinian View of Life. 22.1 – The darwinian revolution challenged traditional views of a young earth inhabited by unchanging species . Historical Setting – Earlier views 1) Scala naturae (Aristotle 384-322 BC)

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Chapter 22

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  1. Chapter 22 Descent with Modification: A Darwinian View of Life

  2. 22.1 – The darwinian revolution challenged traditional views of a young earth inhabited by unchanging species • Historical Setting – Earlier views • 1) Scala naturae (Aristotle 384-322 BC) • Life-forms could be arranged on a scale of increasing complexity • 2) Old Testament • Perfect species were individually created by God

  3. 3) Carolus Linnaeus (1707-1778) • Grouped species into general categories based on the pattern of their creation • Taxonomy • Naming and classification • Binomial Nomenclature • 2 part naming system that includes Genus species

  4. Historical setting (contd.) • 4) Georges Cuvier(1769-1832) • Opposed evolution • Advocated catastrophism – the events in the past happened suddenly and by different mechanisms then today • 5) Charles Lyell (1797-1875) • Uniformitarianism • Earth’s processes have not changed – Earth must be OLD • Darwin studied his work

  5. 6) Jean-Baptiste de Lamarck (1744-1829) • Early evolution: • 1) use and disuse • 2) inheritance of acquired characteristics

  6. 22.2 – Descent with modification by natural selection explains the adaptations of organisms and the unity & diversity of life • Darwin’s voyage on the HMS BEAGLE from 1831-1836 was the time that he developed his theory of evolution by natural selection • Darwin’s idea focused on natural selection vs. Lamarck’s idea focused on inheritance of acquired traits

  7. Natural selection describes how adaptations arise: • Adaptation = characteristics that enhance organisms’ ability to survive & reproduce in specific environments • Example: desert foxes have big ears, arctic foxes have small ears • Natural selection = process in which individuals that have heritable characteristics survive & reproduce at a higher rate than others individuals • Over time, NS can increase the match between organisms & environment • NS may result in adaptations to new conditions, potentially giving rise to new species

  8. Artificial selection • The process by which species are modified by humans • Example: selective breeding for milk or meat production, etc • Individuals do not evolve. POPULATIONS evolve

  9. Origin of Species published in 1859 • Darwin developed two main ideas: • Descent with modification explains life”s unity and diversity • Natural selection is a cause of adaptive evolution

  10. Tree of life Branches represent diversity

  11. Darwin describe four observations of nature and drew 2 conclusions from these • Observation #1: Members of a population often vary greatly in their traits • Observation #2: Traits are inherited from parents to offspring • Observation #3: All species are capable of producing more offspring than the environment can support • Observation #4: Due to lack of food or other resources, many of these offspring do not survive

  12. Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals • Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations

  13. Summary of natural selection • Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals • Natural selection increases the adaptation of organisms to their environment over time • If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

  14. 22.3 Evolutionary evidence

  15. Direct observations • 1) Intense predation of wild guppies results in more drably colored mates • 2) Evolution of drug-resistant viruses and antibiotic-resistant bacteria

  16. The fossil record • Traces of organisms from the past • Commonly found in sedimentary rock • Paleontology = the study of fossils • Fossils show evolutionary changes that have occurred over time & the origin of major new groups of organisms

  17. Homology & Convergent Evolution • 1) Homology • Characteristics in related species can have similarities even with different functions • 2) Homologous Structures • Anatomical sign of evolution • Examples – forelimbs of mammals that are now used for various purposes • Flying in bats • Swimming in whales • Once used for walking

  18. 3) Embryonic homologies • Comparison of early stages of animal development reveals homologies in embryos that are not present in adults • All vertebrate embryos have a post-anal tail & pharyngeal pouches

  19. Vestigial organs • Structures of marginal importance • Remnants of structures that were useful in ancestors • Remnants of pelvis & leg bones in snakes

  20. 5) Molecular homologies • Shared characteristics on the molecular level • All life forms use DNA & RNA • 6) Convergent evolution • Explains why distantly related species can resemble one another • Has taken place when two organisms developed similarities as they adapted to similar environmental challenges • Known as analogous • “Similar problem, similar solution”

  21. Homologous = evidence of relationAnalogous = similar function & solution

  22. Biogeography • The geographic distribution of species • 1) species in a discrete geographic area tend to be more closely related to each other • South American desert animals are more closely related to local animals in other habitats than they are to the desert animals of Asia

  23. 2) Continental drift • The movement of the tectonic plates • The break-up of Pangaea • Explains the relation of species on different continents

  24. 3) Endemic species • Found at a certain geographic location and nowhere else • Marine iguanas are endemic to the Galapagos • 4) Darwin’s theory of evolution through natural selection explains the succession of forms in the fossil record • Transitional fossils have been found that link ancient organisms to modern ones

  25. summary • 1) Evolution is change in species over time • 2) Heritable variations exist within a population • 3) These variations can result in differential reproductive success • 4) Over generations, this can result in changes in the genetic composition of the population • INDIVIDUALS DO NOT EVOLVE – POPULATIONS DO

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