<sod>  
 Typically, an analysis begins by collecting information on certain features of all the organisms in question, and then deciding which versions were present in their common ancestor (''plesiomorphies'') and which have been derived since (''apomorphies'').  Usually this is done by considering some ''outgroup'' of organisms we know are not too closely related to any of the organisms in question.  Only apomorphies are of any use in characterising cladistic divisions.
 
Next, different possible cladograms are drawn up and evaluated.  Clades are typically drawn so that they can have as many synapomorphies as possible.  The idea is that a sufficiently large number of characteristics should be large enough to overwhelm any examples of [[convergent evolution]].  In other words, there are many ways in which plants and animals, etc., may evolve features that resemble each other because of environmental conditions.  A well-known type of convergent evolution is insect mimicry, in which some insects that are edible come to superficially resemble other insects that are inedible, and so escape being eaten.
 
 In practice, neutral features like exact ''ultrastructure'' (a term for extremely fine structure, microscopic or molecular composition of cellular structure) tend to do just that, to provide evidence for real relationships even when the appearance of organisms makes it otherwise difficult.  When equivalent possibilities turn up, one is usually chosen based on the principle of ''parsimony'': the most compact arrangement is likely the best (a variation of [[Occam's razor]]).  Another approach, particularly useful in molecular evolution, is [[maximum likelihood]], which selects the optimal cladogram that has the highest likelihood based on a specific probability model of changes.
 
 <eod> <sod> 
 Typically, an analysis begins by collecting information on certain features of all the organisms in question, and then deciding which versions were present in their common ancestor (''plesiomorphies'') and which have been derived since (''apomorphies'').  Usually this is done by considering some ''outgroup'' of organisms we know are not too closely related to any of the organisms in question.  Only apomorphies are of any use in characterising cladistic divisions.
 
Next, different possible cladograms are drawn up and evaluated.  Clades are typically drawn so that they can have as many synapomorphies as possible.  The idea is that a sufficiently large number of characteristics should be large enough to overwhelm any examples of [[convergent evolution]].  In other words, there are many ways in which plants and animals, etc., may evolve features that resemble each other because of environmental conditions.  A well-known type of convergent evolution is the evolution of wings. Though the wings of birds and insects may superficially resemble one another and serve the same function, both evolved independently. 
 
 In practice, neutral features like exact ''ultrastructure'' (a term for extremely fine structure, microscopic or molecular composition of cellular structure) tend to do just that, to provide evidence for real relationships even when the appearance of organisms makes it otherwise difficult.  When equivalent possibilities turn up, one is usually chosen based on the principle of ''parsimony'': the most compact arrangement is likely the best (a variation of [[Occam's razor]]).  Another approach, particularly useful in molecular evolution, is [[maximum likelihood]], which selects the optimal cladogram that has the highest likelihood based on a specific probability model of changes.
 
 <eod>