Cladistic taxonomy: weird spinoff of Darwinism
Here are some good reasons for teaching Darwinism:
(1) Being familiar with Darwinism is part of being an educated person because it is widely accepted among scientists.
(2) For scientists, knowing Darwinism is necessary for understanding cladistic taxonomy and some scientific papers.
One reference says about cladistic taxonomy,
The Linnaean system is still used in some branches of biology. But in other branches, and particularly in vertebrate paleontology, it is rapidly being replaced by a system referred to as cladistics or phylogenetic systematics. Cladistics was invented by the German entomologist Hennig in the 1950s, but the basic methods of cladistics were devised in the 19th century by philologists attempting to reconstruct the histories and interrelationships of European languages.
Another reference says,
The basic idea behind cladistics is that members of a group share a common evolutionary history, and are "closely related," more so to members of the same group than to other organisms. These groups are recognized by sharing unique features which were not present in distant ancestors. These shared derived characteristics are called synapomorphies.
Note that it is not enough for organisms to share characteristics, in fact two organisms may share a great many characteristics and not be considered members of the same group. For example, consider a jellyfish, starfish, and a human; which two are most closely related? The jellyfish and starfish both live in the water, have radial symmetry, and are invertebrates, so you might suppose that they belong together in a group. This would not reflect evolutionary relationships, however, since the starfish and human are actually more closely related. It is not just the presence of shared characteristics which is important, but the presence of shared derived characteristics. In the example above, all three characteristics are believed to have been present in the common ancestor of all animals, and so are trivial for determining relationships, since all three organisms in question belong to the group "animals." While humans are different from the other two organisms, they differ only in characteristics which arose newly in an ancestor which is not shared with the other two.(emphasis in original)
So a starfish is more related to humans than to jellyfish? Is this the sort of stuff they are talking about when they say that "nothing in biology makes sense except in the light of evolution"?
Of course, there is some arbitrariness in traditional Linnaean taxonomy as well. For example, it is somewhat arbitrary to regard bats and cetaceans as mammals with some avian and ichthyic features, respectively, rather than as birds and fish with mammalian features. But cladistic taxonomy carries the arbitrariness to a whole new level.
Labels: Evolution controversy (2 of 4)