Natural Selection Notes

Adaptability—ability of an organism to change to better survive in its environment

Environment—the physical, biological, and chemical factors that affect an organism where it lives

     Habitat—set of environmental conditions where an organism naturally lives

*the environment can influence the traits that are expressed by an organism*

 

Charles Darwin—19th century (1800s); natural scientist

  • Asked some important questions:
    • “Why are organisms different?”
    • “Why are organisms the same?”
    • “Why are there so many different types of animals?”
  • discovered idea of natural selection—one of science’s most important concepts

 

Natural Selection (or “Survival of the Fittest”)

  • individuals in a species, with genes that are the best suited to survive changes in the environment, are the ones that live and reproduce
    • the one with genetic advantages is most likely to live and pass on its genes
      • increases the presence of the better genes in the species, until eventually it becomes a characteristic of that species

1859: Charles Darwin published “On the Origin of Species by Means of Natural Selection”

  • based on over 20 years of research, starting with a 5 year trip on the HMS Beagle
  • visited Galapagos Islands, where most famous/important research was done
  • chain of 16 volcanic islands near the equator, west of South America
  • isolated, so many species are found nowhere else on Earth
    • Darwin observed that the same animal was different on each island:

    Galapagos Iguanas:

    On one island:

    iguana spent most of its time in the ocean, swimming and diving for seaweed

     (Marine Iguanas)

    On another island:

    iguanas lived on land and ate cactus

    (Land Iguanas)

     

    Giant Tortoises (so big 2 people could ride them)

    • giant tortoises found only in the Galapagos; only about 200 remain today
    • traits helped them find food/survive in different environments
    tortoises on islands with plants near the ground had rounded shells and shorter necks tortoises on islands with tall shrubs had longer necks and shells that bent upwards

     

    Darwin’s Finches

    • most studied species on Galapagos

    • Darwin didn’t originally realize they were finches and related
    • each island has its own version
    • beaks differed in size and shape, and matched the food resources on the birds’ islands
    • all came from the same finch ancestor, and adapted to eat seeds that existed on each home island

    **Natural Selection leads to evolution of a species**

     

    Evolution—change in inheritable traits over successive generations (ultimately developing new species)