Weighting against homoplasy improves phylogenetic analysis of morphological data sets
Article first published online: 13 MAR 2008
© The Willi Hennig Society 2008
Volume 24, Issue 5, pages 758–773, October 2008
How to Cite
Goloboff, P. A., Carpenter, J. M., Arias, J. S. and Esquivel, D. R. M. (2008), Weighting against homoplasy improves phylogenetic analysis of morphological data sets. Cladistics, 24: 758–773. doi: 10.1111/j.1096-0031.2008.00209.x
- Issue published online: 29 SEP 2008
- Article first published online: 13 MAR 2008
- Accepted 10 December 2007
The problem of character weighting in cladistic analysis is revisited. The finding that, in large molecular data sets, removal of third positions (with more homoplasy) decreases the number of well supported groups has been interpreted by some authors as indicating that weighting methods are unjustified. Two arguments against that interpretation are advanced. Characters that collectively determine few well-supported groups may be highly reliable when taken individually (as shown by specific examples), so that inferring greater reliability for sets of characters that lead to an increase in jackknife frequencies may not always be warranted. But even if changes in jackknife frequencies can be used to infer reliability, we demonstrate that jackknife frequencies in large molecular data sets are actually improved when downweighting characters according to their homoplasy but using properly rescaled functions (instead of the very strong standard functions, or the extreme of inclusion/exclusion); this further weakens the argument that downweighting homoplastic characters is undesirable. Last, we show that downweighting characters according to their homoplasy (using standard homoplasy-weighting methods) on 70 morphological data sets (with 50–170 taxa), produces clear increases in jackknife frequencies. The results obtained under homoplasy weighting also appear more stable than results under equal weights: adding either taxa or characters, when weighting against homoplasy, produced results more similar to original analyses (i.e., with larger numbers of groups that continue being supported after addition of taxa or characters), with similar or lower error rates (i.e., proportion of groups recovered that subsequently turn out to be incorrect). Therefore, the same argument that had been advanced against homoplasy weighting in the case of large molecular data sets is an argument in favor of such weighting in the case of morphological data sets.
© The Willi Hennig Society 2008.