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Classifications Based On Evolutionary Ancestry: An Overview of Cladistics

written by: Emma Lloyd • edited by: Donna Cosmato • updated: 8/26/2012

Have you ever heard of cladistics? It is a somewhat obscure field dealing with the evolution and classification of species that has some surprising applications in modern medicine.

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    What Is Cladistics?

    Cladistics is the study and classification of species based on their evolutionary ancestry. Unlike other classification systems, it focuses on the evolutionary relationships between species, rather than their current similarities.

    Cladistics analysis involves gathering data such as genome sequence and physical characteristics of the species under study, including aspects such as skeletal anatomy, biochemical information, and perhaps obvious physical characteristics such as color, patterns, or markings. Using this information, the research constructs a cladogram (also called a phylogenetic tree) which represents the possible evolutionary relationships between the various species being studied.

    Why is this useful? Why is it important to know how and when species evolved?

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    Real-Life Applications of Cladistics

    Biologists can use cladistics and cladograms to solve problems and make predictions that expand our knowledge of evolution or even solve current problems in medical science.

    One rather well-known example is how scientists used knowledge of evolutionary relationships, together with knowledge of physical characteristics of species, to determine the true evolutionary ancestors of whales.

    Previously it had been thought that the whale’s ancestors were carnivores known as mesochynids, which first appeared in the early Paleocene era (around 65 million years ago) and died out in the early Oligocene era (around 33 million years ago). However, a closers examination of the structure of the whale’s ankle has revealed that it is much more likely their closest evolutionary ancestors were not mesochynids, but rather that whales share their ancestors with hoofed animals such as camels, pigs, hippos, and ruminants. Ancestral whale species share with all of these animals a highly characteristic ankle structure called a "double pulley.”

    As a result of this evidence, many evolutionary scientists now doubt that whales are descended from mesochynids at all. Instead, they theorize that whales are descended from anthracotheres, a family of ungulates, which are the evolutionary ancestors of hippos and also bear some relationship to pigs. Another, stronger theory is that whales evolved from the ungulate family known as artiodactyls after a group of these land-based mammals gradually returned to the water.

    Cladistics is not only useful to researchers seeking to understand evolutionary relationships and processes. Recently, cladistics was used to locate a supply of a compound called Taxol, which is used in treating certain types of cancer. Scientists initially discovered Taxol in extractions from a tree called the Pacific yew. However, it proved expensive and difficult to get enough of the compound to make its use practical.

    Biologists used information about the evolutionary relationships between different species of yew trees to determine where a more easily obtainable source of Taxol might be found. They predicted that Taxol-like compounds would be found in close relatives of the Pacific yew, and their prediction was found to be true when the European yew was tested and found to contain a compound from which Taxol could be derived.

    Cladistics can be used to solve problems not only in biology, but in other disciplines and research areas, too. In a field known as historical linguistics, for example, the principles of cladistics can be used to determine how and when various languages have evolved.