Evolution

• Reproductively isolated


  The inability of species to breed and produce fertile offspring
• Selection


  The process in which a variant is more advantageous under certain selective pressures, enhancing its chance of survival and reproduction
• Speciation


  Process of formation of new species
• Stratigraphic method


  The method of obtaining the relative age of an object by its position within a given sequence of rock strata
• Sympatric speciation


  Speciation that occurs between two populations that have no geographical barrier between them
• Trace fossils


  Preserved evidence of the activities of organisms, such as footprints, toothmarks, tracks, burrows and coprolites
• Transitional fossil


  The fossilised remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group(s)
• Variation


  Differences exhibited among members of a population owing to the action of genes
• genetic drift 


  random changes, unpredictable in direction, in allele frequencies from one generation to the next owing to the action of chance events
• gene flow


  the movement of alleles between interbreeding popluations
• prezygotic isolation examples

  Temporal

  Mechanical

  Behavioural

  Habitual

  Geographical
• Homologous structures


  similar features in organisms with the same ancestor. eg: mammal forearm
• physical agent selective pressures


  climate change, food shortage, shelter availability
• natural selection

  when allele frequencies change in a population gene pool due selection pressures creating selective advantage for particular phenotypes
• biological fitness


  reproductive sucess