• Basic idea: “Descent with modification, change in genetic composition over time from generation to generation”
  • Specific: the process by which frequency of heritable traits in population changes from one generation to the next
  • A population is evolving if their allele frequencies are changing
    • Model for evolution: survival and reproduction

Evolution: Earlier Theories

  1. Use and disuse: describe how body parts of organisms can develop with increased usage while unused parts weaken → idea was correct like among athletes

Inheritance of acquired characteristics: described how body features acquired during an  organism’s lifetime (ex: muscle bulk) could be passed onto offspring → idea was incorrect bcuz only genetic material of cells can be passed on

  1. Catastrophism: The reason for different fossils in different strata of rocks was because of mass extinction events (true)
  • Strata: layers of rock

Evidence for Evolution

  1. Paleontology: provides fossils of extinct species → changes in species and formation of new species can be studied
  • Fossils removed from successive layers of sediment (deeper = older) show gradual changes alternating with rapid changes
    • Large, rapid changes produce new species
  • Age of fossils determined using C-14 dating; older = less C-14
  1. Biogeography: the study of the distribution of species → reveal that unrelated species in different regions in the world look like when found in similar environments
  • Ex: rabbits did not exist in Australia until introduce by humans → native Australian wallaby resembles rabbit both in structure and habit
  1. Embryology: reveals similar stages in development among related species → similarities establish evolutionary relationships
  • Gill sites, arches, and tails are found in mammal embryos
  1. Comparative Anatomy: describes two kinds of structure used to establish evolutionary relationships among species + there are heritable variations among individuals
  1. Homologous Structures (homologies): body parts that resemble one another in different species because have evolved from a common ancestor
  • Anatomy may by modified for survival in specific environments→ homologous structures may look different, but will resemble one another in pattern (Similar structure, diff function)
  • Forelimbs of cats, bats, whales, and humans are homologous bcuz evolved from common mammal
  • Vestigial Structures: body parts that used to serve function in common ancestor but not anymore
    • Ex: remnants of limbs in snakes, hindlimbs in whales, and wings of flightless birds
  • More recent homologous characteristics shared by smaller group
  1. Analogous structure (analogies): body parts that resemble one another in different species, not because evolved from common ancestor, but because evolved independently as adaptations to similar environment (similar structure and function)
  • Ex: fins and body shapes of sharks, penguins, whales, and poiposies bcuz are adapted to swimming
  • Results from Convergent Evolution: when similar environmental pressures and natural selection produce similar traits in unrelated organisms
    • Homoplasy: trait species share due to convergent evolution
  1. Molecular Biology: examines nucleotide and amino acid sequences of DNA and proteins from diff species
  • Closely related species share higher % of sequences than distantly related species
    • More than 98% of sequences in humans and chimpanzees are identical
      • Shows how morphology is not only way

                             Distantly related species have different DNA bases and lengths bcuz of  deletions & insertions

  • Molecular data more accurate/reliable bcuz directly shows genetic makeup
  • Bcuz of redundancy of the genetic code, gene bases in different species can differ slightly and produce same protein
  • Use base sequences NOT base-pair percentages to infer relatedness