Molecular Systematics
Molecular systematics is the use of molecular genetics to study the evolution of relationships among individuals and species. The goal of systematic studies is to provide insight into the history of groups of organisms and the evolutionary processes that create diversity among species.
For thousands of years, naturalists have looked at the world and attempted to describe and explain biological diversity. This attempt to examineand classify is called systematics—a system for imposing order on the seeming chaos of nature. In 1758 Swedish naturalist Carolus Linnaeus devised a hierarchical classification system using two-part Latin names to categorize plants and animals. This system is still used today. Linnaeus was opposed to the theory of evolution, and his system was originally based on morphological features of structure and form. However, evolutionists rapidly adopted the Linnaean system and developed it into a classification based on phylogenetics, the evolutionary development of species. By 1866, German zoologist Ernst Haeckel had published a collection of detailed phylogenetic "trees" depicting what was then known about the evolutionary history of life.
Classes of macromolecules. Redrawn from Johnson, 1998.Interest in phylogeny waned over much of the nineteenth century, replaced by an emphasis on genetics, physiology, and geographic variances. That began to change with the work of botanist Walter Zimmerman in the 1940s, and German zoologist Willi Hennig, in the 1950s and 1960s. These scientists pioneered the definition of objective criteria for determining the shared genetic attributes of living and fossil organisms. A revolution in molecular biology took place in the 1960s. Methods for determining the molecular structure of proteins and amino acids allowed biologists to begin to estimate phylogenetic relationships. The exponential growth of molecular systematics in the late twentieth century is due to a combination of increased sophistication in molecular biology techniques, and computer advances in hardware and software that allow scientists to model large and complex data sets.
Molecular systematists use a variety of techniques to derive phylogenetic trees. Polymerase chain reaction (PCR) is used to investigate variations of DNA on a large scale. Gene amplification is also fundamental to new approaches to DNA fingerprinting. Scientists can use " molecular clocks " to predict both past and future molecular divergences in genes.This theory claims that molecular change is sufficiently constant to determine how current genetic lineages branch off from a common ancestor and to determine when the branching occurred. Genetic markers are used to make inferences about relationships between environment and morphology, as well as physiology and behavior.
The importance of phylogenetic trees, or estimates of evolutionary history, are that they allow biology to be predictive. Much as a chemist can use the periodic table of elements to predict chemical reactions, biologists can use phylogenetic trees to analyze biological variation and make predictions about behavior, morphology, and physiology, as well as biomolecular structure and other biological attributes.
The applications of molecular systematics in medicine are particularly important. The ability to predict the course of evolution allows scientists to track epidemic pathogens, research zootonic viruses (animal viruses that are transmissible to humans), understand the evolution of pharmaceuticals and drug resistance, and make predictions about emerging diseases. For example, phylogenetic studies of a form of influenza called influenza A have revealed reliable evolutionary behavior that can be used to predict how the viruses that cause influenza will evolve. This allows scientists to prepare vaccines for future strains in advance. Research into when simian immunodeficiency virus began to be transmitted to humans is vital to understanding how the transmission occurred and perhaps to prevent future zootonic transmissions.
Phylogeny is also an integral part of interpreting any coevolutionary relationships such as host and parasite. In the example of the coevolution of insects and their host plants, the plants evolve chemical defenses against the insects, who then evolve resistances to the chemicals. Because there are a limited number of chemical defenses available to the plants, researchers looked at whether insects are more likely to stay with the same plant as it evolves, or to switch to plants that contain chemicals to which they are already adapted. Studies of beetle phylogeny shows a closer match to plant chemistry than to plant phylogeny, indicating that the beetles have learned to switch plants as the host evolves new defenses.
Behavioral ecologists use phylogeny to reconstruct the evolution of behaviors. Molecular data can clarify the connections between animals previously thought to be unrelated. For example, flying foxes (Pteropus, also known as fruit bats), in contrast to other bats, have been shown to share significant features of brain organization with primates. These shared features lead scientists to believe that wings and flying evolved independently in these two lineages.
Evolution is not something that just happened in the past. It can be observed in the present and used to predict the future, by employing molecular systematics to compare data across genes, individuals, populations, and species.
Bibliography
Hillis, David M. Molecular Systematics. Sunderland, MA: Sinauer Associates, Inc., 1996.
Johnson, George B. Biology: Visualizing Life. New York: Holt, Rinehart and Winston, Inc. 1998.
This is the complete article, containing 822 words
(approx. 3 pages at 300 words per page).
