Introduction

The Talk.Origins Archive contains a wealth of information on evolution and also addresses claims of creationists. Among the articles in this archive are introduction to evolutionary theory. It is long (for a web page), but provides a good supplement to the lecture and text material. Major themes in Evolution is another good overview provided by the National Academy of Sciences. This one has lots of illustrations that you can enlarge by clicking. Keep up with the latest evolution headlines. This page is part of the excellent Richard Dawkins site. A key element in Darwin's argument for evolution was the belief that the Earth was very old. To learn more about the age of the Earth and the different geological periods go to the University of California Museum of Paleontology exhibit on Geological Time.

"Nothing in biology makes sense except in light of evolution"

This quote by Theodosius Dobzhansky nicely emphasizes the role of evolution as the most important unifying principle in biology. When we look at nature we may first be struck by the diversity of life. But if we look deeper we begin to appreciate the unity of life as well. This unity reflects the common ancestry of all living things.

This excerpt from Evolution, Science and Society, a white paper written by evolutionary biologists, describes how evolutionary biology has helped answer questions in such disparate fields as molecular biology, developmental biology, physiology and neurobiology. Homologies are traits that are shared by different species because they were inherited from a common ancestor. Examples include the "universal" genetic code, vertebrate forelimbs and the vestigial whale pelvis. This site by Dr. Sally Otto gives a good overview of these and other examples, with illustrations. The distribution of species makes sense only from an evolutionary perspective.  How else to explain the fact that the species on oceanic islands usually resemble, but are different than, those on the nearest mainland. The Galápagos Islands, for example, are home to 13 endemic species of finches, all descended from the same common ancestor that arrived from Ecuador 600 miles to the east. In their Position on the Teaching of Evolution for Voices for Evolution the Biological Sciences Curriculum Study (BSCS) argue that " it is no longer possible to give a complete or even a coherent account of living things without the story of evolution."

History of Evolutionary Thought

Chronology of Evolutionary Thought from Plato to today. Charles G. Messing has put together a nice page on the history of evolutionary thought (starting with Aristotle's Scala Naturae) with numerous links. Carolus Linnaeus developed the modern hierarchical system of classification.  Although not an evolutionist himself, his system provided the foundation for modern evolutionary taxonomy.  William Paley (1743-1805) was a proponent of Natural Theology, the idea that one could infer the power and goodness of God by observing nature. This link gives a brief description of his views. Erasmus Darwin (1731-1802) was Charles' grandfather. He was an accomplished naturalist and argued for evolution before his grandson was even born. Thomas Malthus (1766-1834) was an economist concerned with human overpopulation. His book, Essay on the Principle of Population (1798), had a major impact on Darwin. Lamarck is sometimes not given sufficient credit for his contribution to evolutionary thought. This site helps set the record straight. Alfred Russel Wallace (1823 - 1913) developed the theory of natural selection independently of Darwin.  Here is another Wallace page. Thomas H. Huxley (1824-1895) was called "Darwin's bulldog" because of his fierce defense of evolutionary theory. He was also a brilliant scientist in his own right.

Charles Darwin
Charles Robert Darwin was an interesting character, as you can see in this short biography. Charles F. Urbanowicz has written a much longer biography with particular emphasis on the "human side" of Darwin. See what started all the fuss; read On the Origin of Species on-line (then go out and buy yourself a copy; every biologist should have one). The text is also available on the Secular Web. Darwin spent most of his adult life at Down House, his country home in Downe near London. This is now open to the public, but if you can't visit at least download a picture of his famous "sand walk" where he did much of his thinking.  Use it as your Windows wallpaper for inspiration.
One of the most memorable places Darwin visited while aboard the HMS Beagle was the Galápagos archipelago. There are several sites on the web that have photographs of the flora and fauna of the islands as well as other information on research and tourism:      The Charles Darwin Research Station      The Wildlife of the Galápagos Islands      Virtual Galápagos

Evidence for Evolution

The fossil record provides direct evidence that life has evolved on this planet. This is referred to as historical evolution (to distinguish it from theories about the mechanisms of evolution) and is considered by most biologists to be an established fact. One line of evidence for historical evolution is the presence of transitional fossils such as those that demonstrate a link between terrestrial mammals and  whales or sea cows. These are sometimes referred to as "missing links" though, of course, once discovered this is a misnomer. One beautiful example of a transitional fossil is Archaeopteryx lithographica, which has both dinosaur and avian features. Chris Nedin has a great site that will answer many of your questions about why Archaeopteryx is so special. Vestigial structures provide clues about a species' evolutionary past. Examples include the vestigial pelvic bones found in modern whales and the tiny hind legs of a fossil snake. (Or is it still a lizard?)

Mechanisms of Evolutionary Change
In the mid-nineteenth century when Darwin and Wallace worked out their theory of natural selection they knew nothing about modern genetics. It was left to those who followed to incorporate genetics and other related concepts into evolutionary theory. This is referred to as the Modern Synthesis.
Next to natural selection, the most important mechanism of evolutionary change is genetic drift, the random fluctuation of allele frequencies. The cheetah is an example of a species with very low genetic diversity, apparently because it passed through a population bottleneck 10,000 years ago or less. This is one form of genetic drift.
Computer simulations are a great way to learn how evolution works. PBS has a couple of online simulations of natural selection. Dr. Rebecca Irwin at the University of Tennessee also has on-line natural selection and genetic drift simulations but without graphics. Try using these simulations to answer the following questions:      Natural Selection Model How does the allele frequency change if you set W(AA)=2, W(Aa)=1.5, and W(aa)=1.0?  (W is the absolute fitness of each genotype.) What if the heterozygote (Aa) has the highest fitness?      Genetic Drift Model (first set the initial allele frequency, p(A), to 0.5) If you repeat the simulation 10 times is the same allele always eliminated? If the size of the population is increased do alleles disappear faster or slower, on average? What do you think would happen if the population size was increased to 5,000? 100,000? Infinity?
Convergent evolution occurs when two species independently evolve similar traits, usually as adaptations to similar habitats or ecological niches. There are many examples of convergence between the marsupial mammals of Australia and placental mammals. Compare, for example, the sugar glider and the flying squirrel, or the marsupial and placental moles. The echidna (a monotreme mammal) is convergent with the porcupine and hedgehog, The University of California Museum of Paleontology has a good site on the convergent evolution of flight in pterosaurs, birds and bats.

Limits to Natural Selection
The ability of species to adapt to their environment is limited since natural selection acts by modifying pre-existing structures. This is referred to as the Panda Principle after the title of an essay written by S. J. Gould in Natural History Magazine. One of the articles in the Talk.Origin Archive, Evidence for Jury-Rigged Design in Nature, addresses the role of historical constraints in evolution. By the way, poor design in nature provides good, albeit indirect, evidence for historical evolution.
The power of natural selection is also limited by the fact that even as a species adapts to its environment, the environment keeps changing. This is especially true for the biotic environment which consists of competitors, parasites, etc. that are also evolving. This principle is called the Red Queen Hypothesis after Lewis Carroll's character in Through the Looking Glass . Another discussion of this hypothesis points out that a co-evolutionary arms-race can actually lead to a decrease in absolute fitness.	Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!

Common Misconceptions about Evolution

I discuss several common misconceptions about evolution in lecture. In a Talk.Origins Archive article Mark Issac lists some additional misconceptions, including the dusty Creationist straw-man, the second law of thermodynamics. A far more insidious view is that natural selection provides some sort of moral or ethical guide for human behavior. This belief is sometimes manifested as Social Darwinism. This just goes to show that a little knowledge, in this case about evolution, can indeed be a dangerous thing. (see also the Talk.Origins Archive article on Evolution and Philosophy.)

Sexual Selection

The Importance of Being Flashy, an article in International Wildlife, gives a fairy good summary of current research on sexual selection, if you can overlook the blatant anthropomorphism. One hypothesis for the evolution of elaborate sexual displays and ornamentation is the handicap principle. A study of sperm competition in zebra finches shows that the male that inseminates a female last fathers most of the offspring. This article from Science Daily introduces the concept of perceptual bias and how it may affect the course of sexual selection, perhaps triggering runaway selection. The extinct Irish elk (actually a deer) had huge antlers. It is likely that these evolved as a result of runaway sexual selection. There is no evidence, however, that the oversized antlers themselves contributed to the species' demise.

The Origin of New Species

Normally we would expect speciation to occur too slowly to be observed in nature. However, there have been some cases of rapid speciation which have been compiled and described by John Boxhom. Punctuated Equilibrium is a mode of speciation proposed by Niles Eldredge and Stephen Jay Gould in 1972. Donald Prothero has written a review of the theory and the controversy surrounding it. The Hawaiian Islands are more than 2,500 miles from the nearest mainland and provide some of the most spectacular cases of species diversification in the world. For example, a recent search of the Bishop Museum insect database for Hawaiian Drosophila (fruit flies) turned up 353 species! Pictures of a few of these flies can be found on the Museum's Diptera Page.

The Fossil Record

• Taxonomy, Transitional Forms, and the Fossil Record by Keith Miller is a bit long, but well worth a look. It gives a good overview of how the fossil record is interpreted and some of the problems involved. He uses lots of pictures to illustrate important evolutionary trends.
• Life first arose on this planet around 3.5 billion years ago. Very gradually single celled creatures evolved into simple multicellular designs (sponges, worms, jellyfish, etc.)  Then at the beginning of the Cambrian period , about 1/2 billion years ago, there was a sudden increase in the number and complexity of species. Within several tens of millions of years, in what is called the "Cambrian Explosion," almost all the major phyla had appeared.
• The Burgess Shale site in the Canadian Rockies provides an intriguing glimpse into the fauna of the Cambrian, which included the aptly named Hallucigenia shown at right. Some of the Burgess Shale species are apparently unrelated to any living forms.
• For a complete introduction to all the geological periods go to the University of California Museum of Paleontology exhibit.
• The trilobites were a very diverse group of marine arthropods, now extinct, that first appeared in the Cambrian period.
• The Mesozoic era is sometimes referred to as the "Age of Dinosaurs." For more information on these magnificent creatures go to my Links page.
• Bones and shells are not the only types of fossils. Some of the most remarkable fossils, because even the soft body parts are preserved, are entombed in fossilized tree resin, also known as amber.
• Radiometric dating is a method for determining the absolute age of fossils.
• Ichnology is the study of trace fossils, which include everything from dinosaur tracks and worm burrows to coprolites (fossilized feces).

Human Evolution

• One of the best sites dealing with human evolution is The Long Foreground: Human Prehistory, a teaching module produced at Washington State University.
• The Origins of Humankind web site is a good source for information on human evolution including news articles on recent discoveries.
• One hot debate going on right now concerns the question of how Homo sapiens arose from H. erectus (sorry for the pun). There is the original multiregional model and the newer monogenesis ("out-of-Africa") model. The latter seems to be supported by molecular (DNA) evidence. For more information, read these articles from Genetics in Practice, Archaeology magazine (part 1, part 2), the BBC and  Scientific American.
• There is an extensive document on Fossil Hominids on the Talk.Origins Archive which also addresses some of the Creationist claims about human evolution
• The Human Prehistory Site provides a brief survey spanning the appearance of Australopithecines up to a few thousand years ago.

Laboratory Exercises
In the first lab exercise of the semester you developed a classification and evolutionary tree of Caminalcules. For a more detailed discussion of this approach take a Journey into Phylogenetic Systematics. (I also have a page devoted to Caminalcules and other examples of "alternate evolution.")
The third lab deals with the evolution of flight. The University of California Museum of Paleontology has an informative site on the physics and evolution of vertebrate flight.

Additional Reading

Hot off the Press: Two online services, Science News and Science Daily often cover stories related to evolutionary biology. The Talk.Origins Archive explores the Evolution/Creationist controversy and much more. This is a great site! Read what the Pope has to say about evolutionary theory (he supports it). For more articles on reconciling science and religion go to the Evolution Resources page sponsored by the AAAS Program of Dialogue Between Science and Religion. (AAAS is the American Association for the Advancement of Science, a prestigious professional organization.) There are often heated debates among evolutionary biologists on a variety of theoretical issues. One of the more entertaining of these debates is an ongoing dispute between two accomplished researchers, Stephen J. Gould and Richard Dawkins. Recently, Gould wrote an essays in the New York Times Book Review slamming a book by Daniel Dennett (Darwin's Dangerous Idea). In the review he also took a swipe at Dawkins. Dawkins, gives as good as he gets as can be seen in his review of a book by Gould. A lot of links to this ongoing debate can be found on John Catalano's site and are well worth exploring for the student interested in the human side of science. (Although some creationists believe that any disagreements among evolutionists must somehow validate their position, nothing could be further from the truth. Debate and disagreement is an important element in scientific advance, though in this case I think it has gotten personal.) The Scopes "Monkey" Trial in 1925 is a famous episode in the ongoing battle between biologists and creationists. In 1960 it was turned into the movie Inherit the Wind with Spencer Tracy and Frederic March. One of the great mysteries about evolution on Earth is how it all began. This article from American Scientist discusses the beginnings of life on Earth. Generally, when we think about evolution we think of life on Earth. But what about life elsewhere in the Cosmos? Currently there is tremendous interest in the possibility of life on Mars. The implications for evolutionary theory are staggering. Currently the best evidence for Martian life comes from meteorites but this evidence is hotly debated. It will probably take a manned mission to Mars to settle the issue.