Evolution and natural selection

• Charles Darwin


  Proposed evolution by natural selection in his book, On the Origin of Species

  
• Alfred Russel Wallace


  Proposed evolution by natural selection independently of Darwin
• Darwin


  • Born into a wealthy English family in 1809
  • Became obsessed with natural history and joined a two-year sailing expedition
  • Abandoned his own medical education
• Wallace


  • Born into a working-class British family in 1823
  • Became obsessed with natural history and aspired to travel the world
  • Trained originally to be a land surveyor
• Both men set off on expeditions to places in the world previously unfamiliar to them
• Adaptations


  Inherited characteristics of organisms that enhance their survival and reproduction in a specific environment
• Both men were struck by amazing examples of adaptations in a wide diversity of organisms (mockingbirds, finches, tortoises)
• Evolution by natural selection (or "descent with modification")


  The process where individuals that are well suited to their environment tend to leave more offspring than others, and over time favorable traits accumulate in the population
• Individuals in a population vary in their heritable characteristics
• Organisms produce more offspring than the environment can support
• Individuals that are well suited to their environment tend to leave more offspring than others
• Over time, favorable traits accumulate in the population
• Natural selection


  A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits
• Evidence for evolution by natural selection

  • Artificial selection
  • Direct observation
  • Fossil record
  • Comparative anatomy
  • Biogeography
• Direct observation


  • Populations of soapberry bugs with shorter mouthparts
  • Populations of peppered moths becoming darker
  • Populations of anoles with longer limbs and larger toepads
• Artificial selection


  The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits
• Artificial selection for particular parts of the wild mustard plant have produced many common vegetables we eat today
• Artificial selection for particular traits has led to the diversification of dog breeds from a single common ancestor—the wolf
• Transitional fossils help show gradual evolutionary change, including in our own recent evolutionary history
• Homology


  Similarity in characteristics resulting from shared ancestry
• Homologous structures


  Structures in different species that are similar because of common ancestry; these similar structures may or may not have similar functions
• Vertebrate forelimbs—although used for many different functions—are structured from homologous bones
• The shared genetic code in all organisms is a homology, and comparisons of our genomes reveal homologous traits all throughout
• Vestigial structures


  A feature of an organism that is a historical remnant of a structure that served a function in the organism's ancestors
• Vestigial structures


  • Vestigial eyes in a subterranean salamander
  • Vestigial legs ("spurs") in a snake
• Convergent evolution


  The evolution of similar features in independent evolutionary lineages
• Convergent evolution


  • Insect wings
  • Bird wings
• Convergent evolution of warning colorations in poisonous frogs
• Biogeography


  The scientific study of the past and present geographic distributions of species
• The distributions of species—both extinct and extant—can teach us about the location and timing of evolutionary events
• Because of this evidence (and so much more), we refer to evolution by natural selection as a scientific theory
• Hypothesis


  Proposed explanation for a phenomenon
• Theory


  Well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment