Natural selection

Directional selection - Directional selection can cause a shift due to environmental changes, different traits have better survival ( decreasing variation) causing a shift in their survival and traits

Disruptive selection - extreme phenotypes are more prevalent instead of middle phenotypes causing the creation of new species due to barriers and isolating genotypes.

Stabilizing selection - removes extreme variation causing less variation that can lead to extinction if organisms are not  able to adapt to any environmental changes.

Speciation

Anagesis - the accumulation of changes in one species that leads to another

Cladogenesis -  the building of one or more species from ancestral species that continue to exist

Genetic Drift

• Genetic drift is a random event that removes alleles, unpredictable that can cause evolution occur (only worlds for small populations)

• Bottleneck effect -  An event that can occur that filters out organism in a randomized order ( typically natural disaster)

• Founder effect - the loss of genetic variation that occurs when a new population is established by 

  Postzygotic

  Developmental isolation

  • Fertilization can occur however embryonic development is irregular, and aborted

  Hybrid inability

  • Hybrid can be conceived and birthed but inevitably cannot reach reproductive age

  Hybrid sterility

  • Hybrid is able to survive to reproductive age, but are sterile and unable to reproduce

  Hybrid elimination

  • Selective hybrid elimination, occurs when sympatric speciation occurs but both species can hybridize (cross breed) and their offspring can reproduce