These examples demonstrate the practical side of phylogenetics. Knowing how different species are related, which species are likely to have inherited which traits, and the patterns of evolution behind the biodiversity we see around us today can help us understand and solve real world problems. As Theodosius Dobzhanksy famously said, “Nothing in biology makes sense except in the light of evolution.”16 Because phylogenies are representations of evolutionary history, they shed light on a wide range of issues within biology. Beyond solving practical problems, evolutionary trees have become an essential tool of modern biological research. You can’t open a scientific journal on genetics, cancer biology, forest ecology, or pretty much any other biological topic without coming across an evolutionary tree. These research problems simply don’t make sense except when they are viewed in the light of evolutionary history. Moreover, phylogenetics helps us satisfy our natural human curiosity. As we look at the natural world around us, evolutionary trees can help us answer the many questions that come to mind: How did the camel get its hump? Why are there so many kinds of beetles? And how did we humans get to be here anyway? To answer any of these questions and many more, scientists and just plain curious folks turn to evolutionary trees.
In school, many of us learned the ranks of biological classification with a handy mnemonic: King (Kingdom), Phillip (Phylum), Came (Class), Over (Order), From (Family), Great (Genus), Spain (Species). This nested hierarchy was developed by Carl Linnaeus in the 18th century and aimed to reflect a divine plan for nature. But times have changed. Today, biologists aim for their classification of life to reflect its evolutionary history. Clearly, phylogenetics has a central role in this endeavor. The idea is that a taxon should be classified and named according to the branch it occupies on the tree of life and that only clades (i.e., complete branches of the tree of life) should given names. This approach is helpful to biologists because a lineage’s evolutionary history factors into all aspects of its biology. It also means that when scientists discover new evidence and revise their hypotheses about the phylogeny of a group of organisms, the names of some of those organisms may have to be changed. When a new species is classified today, it is still (often) assigned a kingdom, phylum, class, and so on, but these have now been redefined so that they refer to particular branches of the tree of life. In addition, species will belong to many clades (which may be named) that fall somewhere in between the seven levels of the Linnaean ranks, providing a more accurate representation of the many levels of diversity of life on Earth. To learn more about phylogenetic classification, visit Evolution 101.
Feeling lost? Review tree basics with the primer.
Find out more about practical applications of evolutionary trees.
General articles about practical applications of phylogenetics:
Applications in conservation:
Applications in medicine:
- Tracking SARS back to its source — using trees to find the source of a new disease
- HIV's not so ancient history — using trees to learn about the situation that allowed HIV to infect humans
- Spreading disease on evolutionary timescales — using trees to investigate the origins of human malaria
- Phylogeny Friday — using trees to identify the source of an HIV outbreak, from ScienceBlogs
Applications in criminal justice:
- Evolutionary evidence takes the stand — using trees to defend health workers accused of infecting children with HIV
- Evolutionary trees help to convict men who knowingly infected women with HIV— using trees to identify the source of HIV infections, from the blog Not Exactly Rocket Science
- Guilty sequence — using trees to convict a doctor who infected his girlfriend with HIV, from Genome News Network
Applications in classification:
Scientific papers about applications of evolutionary trees:
- Ou, C.-Y., C.A. Ciesielski, G. Myers, C.I. Bandea, C.-C. Luo, B.T.M. Korber, … and Epidemiologic Investigation Group. 1992. Molecular epidemiology of HIV transmission in a dental practice. Science 256:1165-1171.
- Hillis, D.M., and J.P. Huelsenbeck. 1994. Support for dental HIV transmission. Nature 369:24-25.
- Willis, C.G., B. Ruhfel, R.B. Primack, A.J. Miller-Rushing, and C.C. Davis. 2008. Phylogenetic patterns of species loss in Thoreau's woods are driven by climate change. Proceedings of the National Academy of Sciences 105:17029-17033.
16 Dobzhansky, T. 1973. Nothing in biology makes sense except in the light of evolution. American Biology Teacher 35:125-129.