Which is more useful in understanding an organism's development into its current form, phylogeny or cladistics?

Phylogeny and cladistics are both important methods used in biology to understand the evolutionary relationships and development of organisms, but they serve slightly different purposes.

Phylogeny refers to the evolutionary history and the relationships between species. It aims to reconstruct the ancestry of groups of organisms and represents these relationships as a phylogenetic tree, often based on morphological or genetic data. Understanding the phylogeny of an organism can provide insight into its development because it helps to trace the lineage of the organism and clarify how certain traits have emerged over time through evolutionary processes.

Cladistics, on the other hand, is a method within phylogenetics that classifies organisms based on shared derived characteristics (synapomorphies) that come from their most recent common ancestor. Instead of just depicting lineage like a family tree, cladistics aims to group organisms into clades, which are branches on the tree of life where each clade represents an organism and all of its descendants. In other words, cladistics is a way of organizing the phylogenetic relationships in a way that reflects how species or groups of species branched off from common ancestors.

To determine which is more useful for understanding an organism's development into its current form is to recognize that they are actually complementary:

Phylogeny provides the broader evolutionary context of an organism, showing not just where it fits within the diversity of life but also how it might have evolved in terms of its physical and genetic traits.

Cladistics offers a framework for classifying the organism within that context, honing in on specific traits that have evolved and the points at which significant evolutionary changes have occurred.

Therefore, the most comprehensive understanding of an organism's development comes from using both phylogenetic and cladistic information together, as they provide a detailed picture of the organism's evolutionary history and its position in the tree of life.