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All in the Family
Test your skills at judging who's who on the tree of life while you learn about the tools and methods of cladistics. |
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Gene Genealogy
This figure illustrates how the alleles of a specific gene in an ancestral species are related to one another. After the ancestral species splits into two daughter species, which in turn give rise to more new species, the most closely related alleles may not end up in the most closely related species. Thus the "gene tree" and the "species tree" may show different branching patterns. |
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Phylogeny: Why Classify?
This graphic illustrates two different approaches to classifying organisms: the phenetic, or classical, approach, which emphasizes structural similarity, and the cladistic, or evolutionary, view, which seeks to group organisms with their closest relatives. |
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Molecular Clocks: Proteins that Evolve at Different Rates
Four different proteins from humans and horses are compared in this graphic and article, and the reasons each protein evolves at its own characteristic rate are discussed. Each protein is useful for measuring evolutionary change over a different time scale. |
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Molecular Evolution: Neutral Drift
This table compares amino acid sequences in cytochrome-c proteins from 20 different species. These differences can be explained by natural selection or by "neutral drift." Cytochrome-c is found in all aerobic cells, from yeast to multicellular organisms. From the number of differences between species we can infer the degree to which they are related. |
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Relationships of Living Species: Calibrating Molecular Clocks
This graphic and article illustrate how comparing hemoglobin from different living species led to the discovery of molecular clocks, and how these clocks can be calibrated with dates from the fossil record. |
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Tree of Life
This diagram and excerpt from Evolution: The Triumph of an Idea by Carl Zimmer illustrate the most recent version of the tree of life -- not a mighty oak with humans at the crown, but a much-branched bush. |
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An Essay on Taxonomy and the Genus Pelusios
This brief article, which originally appeared in Reptile & Amphibian Magazine, explains how taxonomic classification can actually benefit the organisms being classified. Hosted by the University of North Carolina, Chapel Hill. |
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Biodiversity: 21 Species that were
This account by the curator of insects at the Milwaukee Public Museum reveals how difficult and important taxonomic classification is to the study of biodiversity. |
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Biological Diversity: Classification
This site presents a clear-cut and well-illustrated overview of the goals and methods of systematics, including traditional, cladistic, and phenetic ways of classifying. Hosted by Estrella Mountain Community College. |
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Classified!
This site outlines the materials and procedures for an elementary-level activity in which buttons, peanuts, and leaves are classified. The activity provides a simple way to introduce a complex concept to a young audience. Hosted by the Franklin Institute Online. |
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GenBank Taxonomy: Is a Rabbit a Fish?
For advanced students of evolution, this site provides guidance for searching the GenBank for a particular taxon. GenBank has gene sequence information for more than 15,000 species, now organized phylogenetically. Hosted by the National Center for Biotechnology Information. |
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Is it "So Long, Linnaeus"?
Written for those interested in contemporary studies of evolution, this article describes a somewhat radical movement to do away with the Linnaean classification system and taxonomic rankings in favor of a new system based on cladistic relationships. Hosted by findarticles.com. |
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Journey into Phylogenetic Systematics
This site thoroughly and clearly presents the purpose, methodology, and implications of cladistic systematics, which seeks to organize living things by their evolutionary relationships. Also included is an exceptionally useful glossary of phylogenetic terms. Hosted by the University of California Museum of Paleontology. |
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Molecular Biology and Primate Phylogenetics
This activity teaches high school students and above how to infer evolutionary relationships among primates by comparing molecular and anatomical characters. All required materials, except visuals of primate gross anatomy, are included on the site. Hosted by Access Excellence. |
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Molecular Systematics and Conservation Genetics
This site provides answers to many questions concerning the molecular approach to inferring phylogenetic relationships between organisms and includes a list of projects at the Centre for Biodiversity and Conservation. Hosted by the Royal Ontario Museum. |
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NCBI Taxonomy Homepage
For advanced students of evolution, this site contains a database for more than 15,000 species, listed by common and scientific names. Users can get taxonomic classification information, see available molecular information, review relevant primary literature references, and run queries for nucleotide, protein, or genome sequences. Hosted by the National Center for Biotechnology Information. |
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PHYLIP: Phylogenetic Inference Software
This site allows users to download PHYLIP, a free software package that infers evolutionary relationships between taxa using one of a variety of inference methods. PHYLIP is available in several formats and is recommended for advanced students of evolution. |
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Phylogeny Programs
For advanced students of evolution, this site contains a comprehensive list of all known phylogenetics software. It is compiled and updated bi-annually by Joe Felsenstein, creator of PHYLIP phylogenetic inference software, at the University of Washington. |
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Recent African origin of modern humans revealed
This full-text article presents the results of mitochondrial DNA sequencing in humans and great apes. Sequence analysis among groups indicates that humans and chimpanzees diverged only 4.9 million years ago, and supports the theory that the modern human species originated in Africa within the past 150,000 years. Hosted by the Proceedings of the National Academy of Sciences. |
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What is Systematics and why is it important?
This site clearly defines the field of systematics within the context of the biological sciences and describes the kinds of useful information systematic studies provide. Hosted by Ohio State University. |
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Willi Hennig Society: Education
This site for advanced students of evolution provides links to numerous resources, including books, software, and links to other sites. Hosted by the Willi Hennig Society. |
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Evolutionary Biology, 3rd ed.
An excellent college-level textbook for the serious student of modern evolutionary theory. Chapter 5 presents an overview of various classification methods, explains why cladistic analysis has become the phylogenetic method of choice, and discusses how homoplasic charactersc can complicate the analysis. By Douglas J. Futuyma [Sunderland, Mass.: Sinauer Associates, Inc., 1998]. |
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How Many Species are there on Earth?
For advanced students of evolution, this article synthesizes an enormous amount of information to suggest that the roughly 1.5 million described are only a small fraction of the total species currently living on Earth. By R.M. May [Science 241 (1988): 1441-1448]. |
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Hummingbird Species in the Transitional Zones
This segment from Evolution: "Darwin's Dangerous Idea" shows biologists Chris Schneider and Tom Smith studying hummingbirds and other animals in Ecuador. Their research is investigating the processes by which new species are formed. |
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An Origin of Species
Witness for yourself how a new species can evolve as you observe natural selection and adaptive radiation in action. |
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Evolving Ideas: How Does Evolution Really Work?
The process of evolution through natural selection is the focus of this video for high school students, which presents a field study of hummingbird speciation in Ecuador. |
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Isolating Mechanisms: Lacewing Songs
Hear the different songs of three lacewing flies, which serve as reproductive isolating mechanisms between species and determine mate choice. |
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Allopatric Speciation
These images depict Nancy Knowlton's work with snapping shrimp in Panama. Knowlton found that the closing of the isthmus -- dividing the Pacific Ocean from the Caribbean -- resulted in new species of shrimp. |
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Ring Species: Salamanders
This map shows the distribution of the Ensatina salamander on the Pacific coast of the United States, an example of the "ring species" phenomenon. |
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Tigons and Ligers
In captivity, lions and tigers occasionally interbreed, although they are different species and do not mate in the wild. These images of a lion, tiger, "tigon," and "liger" show the blend of physical characteristics seen in such hybrids, which are usually sterile. |
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Biodiversity
This site provides extensive links to information on ecology, different species, and genetic diversity. Hosted by the National Biological Information Infrastructure. |
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Isolating Mechanisms
This site provides clear explanations of how species isolation can occur. Hosted by University College London. |
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Phylogenetics Resources
Suitable for students of phylogenetic analysis, this site provides an exceptional list of meetings, journals, software, Web sites, and other resources. Hosted by the University of California Museum of Paleontology. |
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Pronunciation of Biological Latin
This site provides guidance for the proper pronunciation of scientific names of organisms. |
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Ring Species
This site provides a succinct description of what ring species are, using one of the best-documented examples -- herring gulls of the northern hemisphere. Hosted by the University of Colorado. |
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Scientific American Frontiers: Expedition Panama
This site includes a transcript of a PBS documentary that includes the story of Nancy Knowlton's research on the allopatric speciation of snapping shrimp. Users can also search the video archive for a clip from the show and hear the shrimp snap. Hosted by PBS. |
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Speciation
This site provides a clear explanation for how three basic evolutionary mechanisms -- sympatric, allopatric, and parapatric speciation -- work. Hosted by the University of Miami. |
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Species 2000
This ambitious project seeks to index all Earth's species and remains under construction as the contributing databases continue to input new species and descriptions. Hosted by BIOSIS UK. |
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Systematics, Taxonomy & Nomenclature
This site provides links to a vast array of zoology sites, suitable for audiences from students to professionals. This page presents just one set of those links, focused on the complex topic of biodiversity counts. Hosted by BIOSIS UK. |
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Taxonomy Resources
This site provides the list of all the taxonomic resources, including books, articles, and Web sites, used by GenBank's taxonomy group. Resources are organized by taxon. Hosted by the National Center for Biotechnology Information. |
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The Tree of Life
This is University of Arizona professor David Maddison's online version of the "tree of life." With more than 2,000 Web pages contributed by research biologists worldwide, this site contains information about the diversity of organisms on Earth, their histories, and their relationships to one another. |
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Animal Diversity, 2nd ed.
This college-level text begins with a clear overview of the underlying principles of phylogenetic classification of animals and presents in the subsequent chapters major animal phyla. By Cleveland P. Hickman, Larry S. Roberts, and Allan Larson [Dubuque, Iowa: McGraw Hill College Division, 2000]. |
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Biodiversity: The Fragile Web
This special issue focuses on the Earth's biodiversity, highlighting a few species and ecosystems of special interest, and presenting the reader with overwhelming evidence that humankind is causing a mass extinction of other species. Edited by William L. Allen [National Geographic, February 1999]. |
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Cichlids of the Rift Lakes
In this article, the author explains how the unusual level of diversity found among cichlid fishes in Lake Tanganyika challenges accepted hypotheses about the speed of speciation. By Melanie Stiasny and Axel Meyer [Scientific American, February 1999, 64]. |
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Diversity in Tropical Rain Forests and Coral Reefs
In this now-classic paper for advanced students of evolution, the author proposes that the high biodiversity of tropical rain forests and coral reefs has evolved because of an intermediate level of biological and physical disturbance in these ecosystems. By J.H. Connell [Science 199A (1978): 1302-1310]. |
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Endless Forms: Species and Speciation
This book contains up-to-date information about species concepts, speciation modes, reproductive isolating mechanisms, and hybridization. Edited by Daniel J. Howard and Stewart H. Berlocher [Cambridge: Oxford University Press, 1998]. |
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Evolutionary Biology, 3rd ed.
An excellent college-level textbook for the serious student of modern evolutionary theory. Chapter 15 explains the conceptual confusion behind definitions of "species" and provides thorough explanations of reproductive isolating mechanisms. Hybridization -- essentially the reverse of speciation -- is also discussed. By Douglas J. Futuyma [Sunderland, Mass.: Sinauer Associates, Inc., 1998].
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Genetics and Speciation
For advanced students of evolution, this review of molecular studies suggests that genetic analysis might provide the key to solve -- what Darwin himself called the "mystery of mysteries" -- speciation. By J.A. Coyne [Nature 355 (1992): 511-515]. |
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Hybrid Zones and the Evolutionary Process
For advanced students of evolution, this book is a collection of essays on species hybridization, the reverse of speciation, and includes animal and plant case studies. Edited by R.G. Harrison [New York: Oxford University Press, 1993]. |
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Molecular Clock Mirages
For advanced students of evolution, this article briefly reviews the molecular clock hypothesis and discusses four unsuccessful hypotheses attempting to explain why clock rates are so variable. By F.J. Ayala [Bioessays 21,1 (1999): 71-75]. |
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Molecular Systematics, 2nd ed.
For advanced students of evolution, this manual is an invaluable compendium of molecular techniques and clearly explains methods of obtaining and analyzing molecular data. Edited by David M. Hillis, Craig Moritz and Barbara K. Mable [Sunderland, Mass.: Sinauer Associates, Inc., 1996]. |
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Phylogenetic Systematics
For advanced students of evolution, this classic text launched the field of cladistics. By Willi Hennig [Translated by Davis D.D. & R. Zangerl. Urbana, Ill.: University of Illinois Press, 1966] |
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Plant Taxonomy
For advanced students of evolution, this volume clearly and technically explains theoretical concepts underlying systematic biology, incorporating a vast plant taxonomy literature. By Todd F. Stuessy [New York: Columbia University Press, 1990]. |
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Populations, Species, and Evolution
The abridged version of the classic 1963 text Animal Species and Evolution explains the biological species concept in the context of animal evolution. By Ernst Mayr [Cambridge: Belknap, Harvard University Press, 1970]. |
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Speciation and its Consequences
For advanced students of evolution, this collection of symposium papers covers a wide range of topics, from various species definitions to the theory and mechanisms of speciation. Observed speciation events are also described. Edited by E. Otte and J.A. Endler [Sunderland, Mass.: Sinauer Associates, Inc., 1989]. |
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Taxonomy of Taxonomists
For advanced students of evolution, this article argues that the current understanding of how many, and what types of species, are currently living on Earth are skewed by the biases of taxonomists who tend to study large organisms living in accessible places. By K.J. Gaston and R.M. May [Nature 356 (1992): 281-282]. |
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Variation and Evolution in Plants
This classic work explains classification of plant species, many of which do not conform to the biological species definition, and how speciation occurs among plants. By G. Ledyard Stebbins [New York: Columbia University Press, 1950]. |
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What's in a Name? Sometimes More than Meets the Eye
This article provides a humorous review of some of the more unusual, and often hidden-meaning-laden, scientific names assigned to newly discovered species. By Richard Conniff Richard [Smithsonian 27, no.9 (1996): 66-70]. |
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