EVOLUTIONARY RELATIONSHIPS AND TREE DIAGRAMS
There are following problems in the interpretations of the evolutionary tree diagrams:
1. Stowing relationship above the species: The evolutionary-tree diagrams clarify evolutionary relationships and timescales. But these show, relationships among levels of classification above the species. So they are often a source of misunderstanding.
2. Evolution at specie level: Evolution occurs in species groups (populations). It does not take place at higher taxonomic levels.Therefore, showing phyla or classes as ancestral is misleading.
3. Showing modern representatives: Some phyla or classes are shown as ancestral.Modern representatives of these “ancestral phyla–. These have just as long an evolutionary history as animals in other taxonomic groups. These groups may have descended from the common ancestor.
4. Showing modern representatives at tip of branches: All modern representatives of any group of animals should be present at the rips of a “tree branch”. These may be very different from ancestral species. Zoologists use modern representatives for showing general characteristics of an ancestral species. But they never specify details of the ancestor’s structure, function. or ecology.
5. Ladder like progression: The evolutionary trees often show a ladder like progression of increasing complexity. But evolution has often resulted in reduced complexity and body forms that are evolutionary failures. Therefore, this is misleading.
6. Problem of extinction: In many cases, evolution does not produce phenotypes that survive in under conditions. Therefore. extinction occurs. Ihese are not shown in tree diagram.
7. Representation as inverted cone:The common phlogeny is represented as an inverted cone or a tree. This tree has a narrow trunk and many higher branches. It is also misleading. It shows that evolution is a continuous process. It increases diversification. The fossil records show that this is often wrong. For example, 20 to 30 groups of echinoderms (sea stars and their relatives) arc in the fossil record. But there are only five modern groups. This evolutionary lineage underwent rapid initial evolutionary diversification. After the initial diversification, extinctions occur. So there is no further diversification. Paleontologist Stephen J. Gould uses the term contingency (rapidly ) for rapid evolutionary explosion. It is followed by high likelihood of extinction.
Despite these problems, tree diagrams are used in the books. These diagrams give some information about the evolutionary stock.