Long branch attraction

The frequency of true LBA is unclear and often debated,[1][2][3] and some authors view it as untestable and therefore irrelevant to empirical phylogenetic inference.

[4] Although often viewed as a failing of parsimony-based methodology, LBA could in principle result from a variety of scenarios and be inferred under multiple analytical paradigms.

LBA was first recognized as problematic when analyzing discrete morphological character sets under parsimony criteria, however Maximum Likelihood analyses of DNA or protein sequences are also susceptible.

A simple hypothetical example can be found in Felsenstein 1978 where it is demonstrated that for certain unknown "true" trees, some methods can show bias for grouping long branches, ultimately resulting in the inference of a false sister relationship.

These problems may be minimized by using methods that correct for multiple substitutions at the same site, by adding taxa related to those with the long branches that add additional true synapomorphies to the data, or by using alternative slower evolving traits (e.g. more conservative gene regions).

The result of LBA in evolutionary analyses is that rapidly evolving lineages may be inferred to be sister taxa, regardless of their true relationships.

[8] Of course, when dealing with empirical data in phylogenetic studies of actual organisms, we never know the topology of the true tree, and the more parsimonious (AC) or (BD) might well be the correct hypothesis.