The phenomena of convergent evolution, parallel evolution, and evolutionary reversals ( collectively termed " homoplasy " ) are evolutionary forces that may disrupt the effectiveness of the maximum parsimony method of inferring phylogenetic relationships.
32.
The trees which maximize the concave function of homoplasy resolve character conflict in favour of the characters which have more homology ( less homoplpasy ) and imply that the average weight for the characters is as high as possible.
33.
However, homoplasy is often not evident from inspection of the character itself ( as in DNA sequence, for example ), and is then detected by its incongruence ( unparsimonious distribution ) on a most-parsimonious cladogram.
34.
The retention index ( RI ) was proposed as an improvement of the CI " for certain applications " This metric also purports to measure of the amount of homoplasy, but also measures how well synapomorphies explain the tree.
35.
A value of 1 indicates no homoplasy; 0 represents as much homoplasy as there would be in a fully random dataset, and negative values indicate more homoplasy still ( and tend only to occur in contrived examples ).
36.
A value of 1 indicates no homoplasy; 0 represents as much homoplasy as there would be in a fully random dataset, and negative values indicate more homoplasy still ( and tend only to occur in contrived examples ).
37.
A value of 1 indicates no homoplasy; 0 represents as much homoplasy as there would be in a fully random dataset, and negative values indicate more homoplasy still ( and tend only to occur in contrived examples ).
38.
The remaining similarities between birds and alvarezsaurs, like the keeled sterna, are another case of homoplasy; where the derived alvarezsaurids developed birdlike characters through convergent evolution, rather than inheriting them from a common ancestor with birds.
39.
In some cases, repeated analyses are run, with characters reweighted in inverse proportion to the degree of homoplasy discovered in the previous analysis ( termed successive weighting ); this is another technique that might be considered circular reasoning.
40.
However, pronounced conflict in distance data, which represents an amalgamation of many characters, is less likely due to error or homoplasy unless the data are strongly biased, and is thus more likely to be a result of reticulation.
