Origin of New Species

The Origin of New Species #

• ecological isolation (physical barriers)
• reproductive isolation
  • different mating schedule
  • different sexual behaviors
  • mechanical differences
• incompatible gametes
• hybrid inviability: fertilization possible but zygotes do not survive
• hybrid sterility: hybrid species can breed but offspring cannot

isolation creates new species

Gene Selection #

• isolated populations will evolve differently (genetic drift)
• more separation ⇒ more incompatibility ⇒ less breeding ⇒ new species

Adaptive Radiation #

• when subpopulations adapt to new ecological niches differently

• 3 circumstances:

  1. no similar/competing species
  2. new environment
     • mass extinction
     • migration
  3. species is generalized
     • already has multiple skills/features and can easily survive

• already has multiple skills/features and can easily survive in new environments

  • example: humans

Darwinian Gradualism #

• the tree of evolution
• lots of little branches diverge, but main branch slowly, gradually changes to new species (microevolution)
• challenged by modern fossil record
  • species are stable for a long time, then suddenly change
  • not gradual change, but macroevolution/punctuated equilibrium
  • natural selection is like an “editor” of species, while genetic drift/flow/mutation are the “writers”

Review #

• Mutation is only new variation
• Gene flow/drift mix variation
• Natural selection shapes variation
• Segregation, independent assortment allow for new combinations