cladistique

Cladistique is a method of classifying organisms based on shared derived characteristics, known as synapomorphies. This approach seeks to reconstruct the evolutionary relationships between groups of organisms, or clades, by identifying common ancestors. A clade is defined as a group that includes a common ancestor and all of its descendants.

The core principle of cladistics is that groups of organisms should be classified based on their evolutionary history rather than solely on outward similarities, which can sometimes be misleading due to convergent evolution. Convergent evolution occurs when unrelated organisms develop similar traits independently due to similar environmental pressures.

In cladistic analysis, scientists construct phylogenetic trees, also called cladograms, which are branching diagrams that visually represent the hypothesized evolutionary relationships. These trees are built by analyzing a range of data, including morphological, genetic, and behavioral traits. The branching points on the tree represent hypothetical common ancestors, and the branches represent lineages.

The objective is to create classifications that accurately reflect evolutionary descent. This means that a valid taxonomic group, according to cladistics, must be monophyletic, meaning it includes an ancestor and all of its descendants. Groups that do not meet this criterion, such as paraphyletic or polyphyletic groups, are generally considered problematic in cladistic classification.