This new classification system was developed by German entomologist Willi Hennig in the 1960s. It purports to trace lines of evolutionary descent, but the branches are discovered through a formal process of identifying what groups of creatures share a lot of features in common and what groups exhibit distinct new departures from those ancestral traits. Each shared character state is considered a potential piece of evidence for grouping organisms together. This system now is conducted by computers working on large datasets. Initially however there was a lot of opposition to this system.
In 1979, the British Museum of Natural History used a cladistic analysis to present dinosaur relationships. The next year the museum used a similar approach to present “Man’s Place in Evolution.” At that time there were a lot of scientists who said the branching pattern told them nothing about evolution. In a letter to Nature, British paleontologist Beverly Halstead (Nature 292, July 30, 1981) declared that in the cladistic display on man, the museum was “crudely distorting the evidence.” [p. 403] He further insisted that “the Hennigian or classical cladistics is antagonistic to the gradualist type of evolution.” He blamed colleague Colin Patterson and others for using cladistics to show evolution in a poor light. Dr. Patterson retorted that “much of neo-Darwinism, or the synthetic theory [evolution], may be empty rhetoric.” [p 404 cited in letter]. However now cladistics is almost exclusively used to look for evolutionary relationships among organisms.
For example, in 1997 some biologists looked at a group of animals with a specific pattern of embryonic development (protostomes). Among these animals they discovered a group that have in common a specific molecular structure for a large component of ribosomal RNA and these organisms also uniquely share the feature of growing by molting an exoskeleton. Thus, they declared that all these organisms are a clade or a group with shared ancestry from which they diverged over time. The group is called the ecdysozoa and it consists of very tiny nematodes (tiny round worms with almost no differentiation into tissues and organs) and arthropods which are extremely complex with jointed appendages including wings, large compound eyes and astonishing diversity. Many of the nematodes are parasites found in people and larger animals. These two groups of animals could scarcely be less alike!!! Some people initially objected to the grouping of these two kinds of animal in a common exclusive line of descent. Apparently however this clade is well accepted today.
According to current cladistic systems of classification higher plants and green algae are clustered together in a clade called Archaeplastida. This group excludes Coccolith algae which are responsible for huge chalk deposits, algae with plastid pigment colours other than green, and also Euglena (which are green) but exhibit other features not common to the large group. And the clade Opisthokonta includes all many-celled (metazoan) animals. This group excludes amoebas and a few obscure motile single cells. Formerly fungi were grouped with plants. Now they are mostly grouped with animals. (See protozoan for detailed discussion of this taxonomy)
The practice of cladistics involves a lot of new terminology. For example: homoplasy is the term for a shared character that did not arise from a common ancestor. A more common word for this phenomenon is convergence. Synapomorphy is another common term. It refers to a trait that is present in an ancestral population and is shared exclusively by its evolutionary descendants.
Cladistic lines of descent can be sensitive to what data are included in a dataset for analysis. Thus, different authorities may promote different phylogenetic (evolutionary) trees. Whether the differences actually reflect anything about fitness or not, is not really considered a relevant question. At least former systems based on appearance and function were logical and easier to compare different organisms. It is obvious that the answers one obtains, depend on the system of analysis which one uses.
Creationists use similar computer programs to identify “discontinuities”, that is major breaks in relationships between groups or the created kinds. Often the discontinuities are identified at the family level or lower.