Forces of Evolution

• macroevolution


  the process by which new species are formed from pre-existing species over a long period of time
• microevolution


  changes in the genetic constitution of a population between generations
• evolution is characterised by change
• migration


  movement of an individual between populations
• migrations means the movement of the individuals alleles and genes
• gene flow


  movement of genes between populations
• forms of gene flow include pollen, seeds, and between species
• gene flow always involves the exchange of genetic material
• gene flow between populations maintain species integrity
• lack of gene flow leads to speciation
• speciation


  group of organisms with potential to interbreed and produce viable offspring
• speciation needs both isolation and divergence of a population
• selective is based off of relative fitness
• relative fitness 


  contribution an individual makes to the gene pool of the next generation relative to the contributors of other individuals
• directional selection


  selection against one of the extremes
• directional selection pushes the mean in one direction
• stabilising selection


  selection against both extremes, stabilising everything around the mean
• disruptive selection


  selection against the mean pushing them towards the extremes, lead to speciation
• sexual selection


  individuals with certain characteristics are more likely to obtain mates
• sexual selection leads to sexual dimorphism
• intrasexual selection


  individuals of one sex compete with another for mates of the opposite sex
• intrasexual selection leads to competition or display
• intersexual selection


  individuals of one sex are choosing who they mate with
• intersexual selection is usually done with female choosing male
• diploidy means that some variation are hidden
• balancing selection


  selection maintains multiple forms
• heteozygous has advantages
• selection does not occur with epigenetics
• selection works on variation at that time
• selection is limited by historical constraints
• adaptations are often compromises
• random selection


  selection just by chance, often the result of human activity