Despite their care to code the best qualitative characters in sufficient numbers, the researchers could obtain no perfect phylogenies for some groups, such as Germanic and Albanian within Indo-European. They reasoned that a significant number of characters, which could not be explained by genetic descent from the group's calculated ancestor, were borrowed. Presumably, if the wave model, which explained borrowing, were a complete explanation of the group's characters, no phylogeny at all could be found for it. If both models were partially effective, then a tree would exist, but it would need to be supplemented by non-genetic explanations. The researchers therefore modified the software and method to include the possibility of borrowing.