8.3 Patterns of Evolution

• Convergent Evolution


  Evolution whereby unrelated species independently evolve similar traits to occupy similar ecological niches (food sources, biomes, etc.)
• Divergent Evolution


  A mechanism of macroevolution where many species evolve from a common ancestor over a long period of time
• Divergent Evolution


  • Cats, dogs, humans, whales, and bats arose from a common ancestor as indicated by similar (homologous) bone structure
• These structures, however, have evolved to serve different functions (e.g. swimming, flying, etc.)
• Adaptive Radiation


  Mechanism of microevolution where a single species rapidly (relative to divergence) evolves into many new, distinct species (macroevolution)
• Adaptive Radiation


  • Often occurs with changes in the environment that make new resources available or alter biotic interactions (e.g. predation/parasitism)
• Coevolution


  A process in which two or more species reciprocally affect each other's evolution through natural selection
• Coevolving species may become increasingly dependent on each other
• Coevolution


  • The Madagascar long spurred orchid is pollinated by the hawk moth whose tongue is 30 cm long!
• Macroevolution


  Large-scale evolutionary changes (species formation and extinction)
• Microevolution


  Small scale changes within a population (mutation, natural selection)
• Abiogenesis


  The idea that life arose from non-living things more than 3.5 billion years ago
• The first life-forms were very simple and gradually became more complex
• Experiments attempt to create the environment that may have existed on Earth billions of years ago
• Possible Explanations for Abiogenesis


  • Organic molecules (e.g. amino acids, hydrocarbon chains) can form under natural conditions (building blocks of life)
  • Some RNA molecules are capable of replicating themselves, independent of any other cell components (precursor to self-replicating cells)
• All organisms from each of the 6 kingdoms evolved from one original cell (prokaryote)
• Eukaryotic organisms formed through endosymbiosis


  1. Certain prokaryotic cells were internalized into an ancestral cell

  2. Became mitochondria or chloroplasts

  3. Adding to the complexity of life forms
• Proteobacteria were engulfed by the ancestral eukaryotic cell and would later become known as mitochondria in all eukaryotes
• Cyanobacteria (photosynthetic bacteria) were engulfed by a "more" recent ancestor and would later become chloroplasts in some eukaryotes
• Mitochondria and chloroplasts


  • Can replicate within the cell (like bacteria can)
  • Have double membranes (due to engulfment)
  • DNA sequences and ribosomes found in chloroplast and mitochondria are similar to that of bacteria
• Cambrian Explosion


  The rapid evolution of most major animal phyla that took place during the Cambrian period (start of the Paleozoic era), 542 mya
• Prior to the Paleozoic Era, most organisms were simple single-celled organisms
• Increases in diversity are interrupted by mass extinction events (rapid and widespread decreases in biodiversity)
• ~251 mya, more than 90% of known marine species were eradicated
• Caused by cataclysmic events like tectonic movements, volcanoes, rapid climate change
• An asteroid moving at ~160,000 km/hr hit the Earth, creating a crater 10km deep and 200 km in diameter
• Energy released by the impact would have created super-heated air, Tsunamis 120m high, Dust and smoke blocked sunlight for months→ cold temperatures, Wiped out non-avian dinosaurs
• Cladistics

  A method of determining evolutionary relationships (phylogeny) based on the presence or absence of recently evolved traits
• Derived Trait


  A recently evolved trait
• Synapomorphy


  A derived trait shared by two or more species or groups. Groups with synapomorphies are thought to be more closely related
• Synapomorphies


  • Feathers in all birds
  • Hair in most mammals (except whales)
• Not all similar traits are evidence of relatedness. Traits that evolved independently must be considered separate traits (e.g. bipedalism in humans and birds)
• Evolutionary loss of a trait may be a more recently derived trait
• Evolutionary loss of traits


  • Salamanders and howler monkeys have long tails, but apes do not
• Understanding the pace of evolution allows us to judge how species will respond to climate change and other human-influenced impacts on the environment
• Evolution can occur suddenly - e.g. a single mutation causing polyploidy* can give rise to a new species
• Evolution can occur gradually over millions of years - e.g. evolution of the giraffe's long neck
• Theory of Gradualism


  Species gradually become more distinctive as they evolve
• Large evolutionary changes are due to accumulation of many small changes
• Fossil species represent changing transitional forms