Evolution Methods

Evolution: changes in a species over time, leading to new species

**Theory of Evolution by Natural Selection: inherited traits of a population change over time as the best adapted organisms survive and reproduce, passing on the good traits**

Natural selection occurs when:

  • There is some variation in the inherited traits of organisms in a species
  • Some traits give individuals an advantage over others in surviving and reproducing
  • The individuals with those traits will be more likely to reproduce and pass on traits

 

Other methods of evolution

Speciation: development of a new species

  • only occurs if 2 branches of a species become unable to produce viable offspring

                        (viable = able to survive and reproduce)

Geographic Isolation (or Allopatric Speciation): groups of the same species become geographically isolated for long periods, and become different species

  • separated by mountain ranges, canyons, bodies of water, deserts, etc
    • Example: Squirrels separated by the Grand Canyon
      • Albert Squirrel (on the South Rim)—white bellies and dark tails
      • Kaibab Squirrel (on the North Rim)—black bellies and white tails

*started as one squirrel species, until two populations ended up on opposite sides as the canyon formed; now they’re two separate species that can’t mate

 

Sympatric Speciation: one species evolves into two different species without being separated geographically, generally due to behavioral differences

  • Reproductive Isolation: 2 populations of a species stop mating with each other
    • have different mating locations, mating times, or mating rituals
    • over thousands of years, each population evolves in a different direction

Example: different groups of orcas hunt different species, eat different food, sing different songs, and have different social interactions

**in time, may evolve into different species

 

Species diversity: the number of different species in an area (millions in the world)

  • as environments change, organisms must constantly adapt to those changes
  • high diversity increases the chance that some species will survive
    • Example: asteroid killed dinosaurs, but mammals survived