INVESTIGADORES
MIRANDE Juan Marcos
congresos y reuniones científicas
Título:
On weighting characters differently in different parts of the cladogram
Autor/es:
GOLOBOFF, PABLO A.; MIRANDE, JUAN MARCOS; ARIAS, J. SALVADOR
Lugar:
San Javier, Tucumán
Reunión:
Congreso; A summit of cladistics. 27th Annual Meeting of the Willi Hennig Society and VIII Reunión Argentina de Cladística y Biogeografía; 2008
Institución organizadora:
Willi Hennig Society
Resumen:
One commonly heard criticism of weighting methods such as successive or implied weighting is that they assume uniformity of weights throughout the cladogram. A variant of the same criticism is that current weighting methods rely on the dubious assumption that instances of homoplasy in distant clades are as relevant as instances of homoplasy in more closely related clades. While the assumption of uniformity can hardly be part of a relevant criticism of weighting (sinceequal weighting also assumes it), developing a method which does not assume it may be desirable. Although it is of course possible to run separate analyses, compart- mentalizing the data and using different weights for each part of the tree, the ideal method should consider all the evidence simultaneously and provide a globally optimal solution to the problem. This paper describes a modification of the method of auto-weighted optimization (Goloboff, 1997) to downweight the cost of each character-state transformation according to the number and distance of other transformations between the same states. The method was experimentally implemented, and tested with simulations to confirm that it performs as expected. However, hypothetical examples show that such type of weighting cannot be considered to be a form of parsimony—that is, a form of the criterion that compares trees based on the degree to which similarities can be explained as resulting from common ancestry. If perhaps realistic, the variable-weights criterion necessarily implies that other additional considerations—possibly in conflict with parsimony—come into play. Apparently such undesirable consequences would be a necessary part of any method which weights characters differentially in different parts of the tree. Therefore, uniformity of weights throughout the cladogram seems to be a sine qua non requirement of the parsimony criterion, and parsimony-based weighting methods cannot be criticized for assuming uniformity of weights.