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For Further Reading

Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life.

Reference for: Chapter 12, The Foundations of Evolutionary Theory

Haldane, J. B. S. 1932. The Causes of Evolution. Longman: UK.

Reference for: Chapter 12, The Foundations of Evolutionary Theory

 

*Long, John A. 1995. The Rise of Fishes: 500 Million Years of Evolution. John Hopkins University Press: MD

This lavish overview of the evolution of fishes is not the most detailed but its illustrations and photographs give a rich sense of the evidence on which our understanding of fish evolution is based. It makes a highly readable reference for students and a terrific desk reference for instructors called upon to teach aspects of fish evolution.

Reference for: Chapter 12, Spotlight 12.1

*Raup, David. 1991. Extinction: Bad Genes or Bad Luck? W.W. Norton: NY

This “little” book summarizes the evidence for five major extinctions in the geologic records and their causes. It’s a highly readable and engaging account that will quickly bring the reader up to date on this fascinating topic.

Reference for: Chapter 12, The Foundations of Evolutionary Theory

 

*Stott, Rebecca. 2003. Darwin and the Barnacle: The Story of One Tiny Creature and History’s Most Spectacular Scientific Breakthrough. Norton: NY

This book brings to the forefront Darwin’s painstaking and highly important work on barnacles. It might be argued that Darwin formulated his ideas about evolution and natural selection from studying barnacles. Although this is a “storybook”, in the sense that it weaves a narrative about Darwin’s barnacle work, it does illuminate this important and little known work in an engaging and instructive manner.

Reference for: Chapter 12, The Foundations of Evolutionary Theory

*Carroll, Sean B. 2006. The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution. W. W. Norton: NY

The evolutionary record is contained in the DNA of organisms. It is a history that we can finally begin to read.

 

 

*Coyne, Jerry A., and H. Allen Orr. 2004. Speciation. Sinauer Associates: MA.

Coyne and Orr have written a textbook covering all aspects of speciation, emphasizing modern research on this topic.

 

*Ellis, Richard. 2001. Aquagenesis: The Origin and Evolution of Life in the Sea. Viking Penguin Books: NY

Ellis is a masterful storyteller and illustrator. There are better books on this subject but if you like Ellis way of weaving facts, this book should please you.

 

*Fortey, Richard. 1997. Life: A Natural History of the First Four Billion Years of Life on Earth. Vintage Books: NY

Fortey narrates the history of life on Earth, citing his own work and the research of other scientists to piece together the puzzles of how life evolved.

 

*Fortey, Richard. 2000. Trilobite! Eyewitness to Evolution. Alfred A. Knopf: NY

All you ever wanted to know about trilobites in an engaging, delightful prose.

*Gould, Stephen Jay. 1989. Wonderful Life: The Burgess Shale and the Nature of History. W. W. Norton: NY

Stephen Jay Gould delights some and irritates others but he always manages to inspire thoughtful reflection on a topic. In this book, he discusses in great detail the Burgess Shale and how it paints a picture of the “progression” of evolution unlike what is commonly perceived. Gould sees evolution not only as “survival of the fittest” but also as “survival of the lucky.”

*Gould, Stephen Jay. 2001. The Book of Life: An Illustrated History of the Evolution of Life on Earth. W.W. Norton: IA

*Gould, Stephen Jay. 2002. The Structure of Evolutionary Theory. Belknap Press of Harvard University Press: MA

This immense volume details Gould’s provocative and often controversial views on the evolution of life on Earth. To his credit, Gould is typically entertaining, and this book reads like a good novel. Unfortunately, you have to read a lot of it if you are generally unfamiliar with his ideas or the nuances of evolution. Nonetheless, it’s an essential reference for a biologist’s library.

*Hull, David L. 2001. Science and Selection: Essays on Biological Evolution and the Philosophy of Science. Cambridge University Press: UK

Hull’s essays educate and entertain and get the reader to thinking more deeply about science and its effects on humanity. His essays on evolution are a big help to those who need a refresher or those who require greater ammunition in the verbal wars with antievolutionists.

*Johnson, Kirk R., and Richard K. Stucky. 1995. Prehistoric Journey: A History of Life on Earth. Roberts Rinehart Publishers: CO.

Based on dioramas at the Denver Museum of Natural History, this delightfully illustrated book traces the history of life from microbes to mammals, with an emphasis on dinosaurs. Its brevity notwithstanding, this book does a great job of providing the fossil evidence on which the scientific interpretation of the history of life is based.

*Kirschner, Marc W. and John C. Gerhart. 2005. The Plausibility of Life: Resolving Darwin’s Dilemma. Yale University Press: CT

Kirscner and Gerhart tackle the origins of new species and evolutionary complexity.

*Knoll, Andrew. 2003. Life on a Young Planet: The First Three Billion Years of Evolution on Earth. Princeton University Press: NJ

This is an outstanding book on the evolution of Earth and its biota. Knoll is one of the pioneers in the field of geobiology and his up-to-date scientific account of the field makes this an excellent reference and an entertaining read. Knoll exposes the controversies and examines the evidence that surrounding them. Most narratives don’t make good reference books but Knoll’s is an exception. If you are trying to choose between “histories of life on Earth”, pick this one.

*Larson, Edward J. 2004. Evolution: The Remarkable History of a Scientific Theory. Modern Library: NY

This book sketches the development of evolutionary theory. It’s primarily written for general audiences and so loses some of the detail required for students and instructors.

*Margulis, Lynn, and Dorion Sagan. 1986. Microcosmos: Four Billion Years of Microbial Evolution. Simon and Schuster: NY.

A provocative hypothesis about the interdependency of higher organisms and bacteria.

*Margulis, Lynn. 1998. The Symbiotic Planet: A New Look at Evolution. Weidenfeld & Nicolson: UK

Margulis is not one to shy away from controversy. Her endosymbiotic hypothesis was met with great skepticism originally but is now widely accepted. In this book, she applies her principles of symbiosis to the full range of life and its communities, including Earth.

*Margulis, Lynn, and Michael F. Dolan. 2002. Early Life: Evolution of the PreCambrian Earth, 2nd Edition. Jones and Bartlett: MA

*Mayr, Ernst. 1982. The Growth of Biological Thought: Diversity, Evolution, and Inheritance. Belknap Press of Harvard University Press: MA

Professor Sean thinks this is one of the most important books ever written. It defends the place of biology in science and retells the history of evolutionary thinking from pre- to neo-Darwinism. At more than 900 pages, it’s an intimidating volume, but Mayr’s prose and his way of explaining concepts makes this book a delight to read. You will only want to read several pages of it at a time as Mayr provokes deep reverie with every page. But you will have a more comprehensive and deeper understanding of evolution upon reading this book than is possible with just about any other book.

*Mayr, Ernst. 2001. What Evolution Is. Basic Books: NY

Any book by Ernst Mayr is worth reading, according to Professor Sean. This book provides a solid foundation for different aspects of evolution and evolutionary processes.

*Weiner, Jonathan. 1994. The Beak of the Finch. Vintage Books: NY

This Pulitzer Prize-winning book has become a textbook for learning about evolution.

*Zimmer, Carl. 1998. At the Water’s Edge: Fish With Fingers, Whales With Legs, and How Life Came Ashore but Then Went Back to Sea. Simon and Schuster: NY

An excellent narrative on macroevolution.

*Zimmer, Carl. 2001. Evolution: The Triumph of an Idea. HarperCollins: NY

This is the companion book to the Evolution video series by PBS.

*Moorehead, Alan. 1969. Darwin and the Beagle. Harper & Row: NY

This “old” book is notable for its abundant photos, illustrations and drawings, many of which are full page and stunning, and for its highly readable and intimate account of Charles Darwin’s voyage aboard HMS Beagle. It’s not as dense with information as other books on Darwin but it captures the spirit of his curiosity and scientific reasoning.

Reference for: Chapter 12, The Foundations of Evolutionary Theory

The Endless Voyage: Building Blocks, Water World and Survivors (written by W. S. Chamberlin) (Episodes 18, 19 and 21). 2002 (VHS and DVD). Intelecom.

Professor Sean appeared in several of the episodes of this series and helped develop learning activities to support it. While some episodes are better than others, The Endless Voyage provides one of the most complete and up-to-date series on oceanography available

: : Encyclopedia of the Sea : :
Chapter Two Image

Cetaceans: A Case Study in Macroevolution by Sean Chamberlin

The study of evolution—the change in species over time—involves many aspects beyond the scope of my treatment here. However, the cetaceans offer an ideal example in the study of how the vertebrate body plan was modified from a terrestrial form to an aquatic one. Rapid advances in our knowledge of cetaceans, spurred in part by new fossil finds in Pakistan, India and elsewhere, have provided scientists with “one of the best documented examples of macroevolution in mammals” (Thewissen and Bajpai 2001).

Macroevolution, the evolution of higher-order taxa above the species level, helps to explain trends in evolution that occurred as a result of changes in the global environment, brought about by shifts in climate (with tectonic, biological or astronomical causes, among others), catastrophic events (such as mass eruptions or meteorite impacts) or other causes. Microevolution, the evolution of new species, represents an important part of macroevolutionary processes and modern ecological theory encompasses both (see Mayr 2001; Gould 2002). The global scale events that drive macroevolution may eliminate entire groups of species (higher-order taxa) and provide new habitat that may be exploited by surviving species, i.e., new ecological opportunity (Schluter 2000). The success with which an organism exploits this new environment and diversifies into many species is called adaptive radiation. More formally adaptive radiation may be defined as “the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage.” Fundamentally, it explains how a single ancestor diversifies into a number of species in a diverse environment. For instructors and inquiring minds interested in learning more on these topics, we suggest Ernst Mayr’s What Evolution Is (2001) or the National Science Teacher Association publication Evolution in Perspective (2003).

The exploitation of a shallow marine habitat by a land mammal and its transition to a fully aquatic animal that rapidly diversified throughout the world ocean in response to shifts in climate describes the macroevolution of cetaceans. A brief discussion of this evolutionary history provides insights into how small changes in the body plan of an organism—often brought about by small changes to a single gene or set of genes—can lead to different functions and enable an organism to exploit otherwise unavailable resources. Cetaceans are highly modified mammals but they are mammals nonetheless. The fossil record and a host of other evidence now offer a fairly complete picture of their transition.

Until 2001, scientists held two hypotheses regarding the ancestry of cetaceans. Palaeontological evidence suggested that they came from a wolf-like, mesonychian ancestor, a relative of hooved ungulates like the cow. DNA data supported an origin from an ariodactyl ancestor, an even-toed ungulate like the deer or hippopotamus. Combining morphological, protein and DNA data and adding results from studies of newly discovered cetacean skeletons called pakicetids, scientists now agree that ariodactyls are the base ancestor. However, their relatedness to hippopotamids is not direct. Thewissen suggest that cetaceans and hippos may have shared the same “grandmother” but additional research will be needed to establish these relationships unequivocally (e.g. Thewissen et al., 1998, 2001). Establishing phylogenetic relationships within the Cetacea will also require additional studies. (Berta and Sumich 1999; see also Gatsey et al., 1996).

Nevertheless, modern fossil and molecular evidence allow us to trace the stages in the evolution of early cetaceans, perhaps better than any other animal (Thewissen and Bajpai 2001). The very first fossil cetaceans, called archaeocetes (“ancient whales”) or, on occasion, “experimental Eocene whales” (Thewissen and Williams 2002), appear about 50 million years ago in Pakistan and India, where cetaceans are thought to have evolved in the Tethys seaway. The “experimental” qualifier of these animals stems from the observation that a variety of morphological characteristics typified these animals, serving to provide diverse modes of feeding and behavior in a relatively stable habitat. However, as their habitat was transformed by tectonic, atmospheric and other global processes, most of these experiments went extinct. As Thewissen (1998) puts it: “Cetaceans originated when a Paleogene land mammal underwent a dramatic shift in biological attributes in order to accommodate an enormous shift in habitat.”

These first cetaceans were not aquatic; rather, they walked on all fours and merely spent a great deal of time wading in water. With time, evolution (for reasons speculated below) continued to favor animals adapted for an aquatic life and the cetaceans developed a more “whale-like” posture. The ambulocetidae, a group of early cetaceans—similar to the crocodiles in their habit of waiting in water and ambushing prey on shore—flourished in the Eocene about 49 million years ago. By the late Eocene, approximately 35 to 41 million years ago, the advanced archaeocetes, the basilosaurids and dorudontids, whose fossils are abundant in the eastern United States, had invaded the ocean. With a toothed upper and lower jaw, a horizontally flattened tail and nostrils on top of its head, these whales most closely resemble the modern whales. Though they went extinct at the start of the Oligocene, 34 million years ago, they left behind two very important descendants: the Odontocetes and the Mysticetes.

Cetaceans quickly radiated (diversified into different species) throughout the world ocean about 28–33 million years ago. What is perhaps most remarkable about this feat is how the cetacean body transformed from a terrestrial existence to an aquatic one. Scientists consider cetaceans to be the most highly derived (exhibiting the greatest number of changes) among all mammals. Their skull telescoped—elongated in the anterior-posterior and lateral directions—to accommodate their dorsally migrating nostrils that eventually became their blowhole, the opening through which they breathe. Breathing through the top of their head, as it were, enabled cetaceans to spend less time at the surface, perhaps to avoid predators, and to conserve energy by reducing drag associated with surface swimming. Elongation of the skull and shortening of the neck streamlined their body, further enhancing their hydrodynamic abilities. Evolution of a horizontally flattened tail, called a fluke, provided a highly efficient hydrofoil for propulsion. Loss of the hindlimbs and modification of the forelimbs into flippers for steering completed the morphological transformation to a wholly aquatic life.

The transition to the ocean also required modification of the cetacean sensory system. The limited visual and olfactory environment of the ocean—relative to terrestrial environments—led to complex modifications of the lower jaw and inner ear to accommodate underwater hearing. Sound travels underwater about 4.5 times the speed of sound in air, attenuates much less rapidly than light and travels far more quickly than chemical cues, so hearing has increased greater importance in the ocean. At the same time, limitations imposed by swimming in three dimensions, diving (and equilibrium of the ear) and reliance on echolocation, communication and mating led to additional specializations, many of which are still poorly known. As emphasized on the Paleos web site, the “ear” functions for more than just sensing sound; it also functions in balance and detecting acceleration. These simultaneous demands on the auditory system of cetaceans complicate their evolution and make them more difficult to study. Nonetheless, the study of cetacean hearing has gained prominence in the 21st century. The proposal to use acoustics for measuring rates of ocean warming (acoustic thermometry) and the Navy’s desire to use low-frequency active sonar (LFAS) have prompted outcries over their potential negative effects on cetaceans, including disruption of their hearing. Thus, our study of cetacean hearing takes on added dimensions for interpreting this modern debate.

The ear flaps, or pinnae, of cetaceans are absent, presumably to reduce drag. Ear canals may be present in some species and these are nearly always filled. The air-filled canal between the ear and ear drum—like that found in humans and most other mammals—is absent in cetaceans. Moreover, their ear drum and inner ear bones, while resembling other mammals, are enclosed in a discrete and specialized “foam-filled” bony space separate from the skull, called a tympanoperiotic complex. The ear drum is not a thin membrane but instead consists of a cord-like structure called a tympanic (or tympanoperiotic) bone connected by ossicles (bony structures) to the inner ear. The inner ear contains all the elements common to the human inner ear, including the semicircular canals, which are much more compact and reduced in size relative to the size of the animal. In fact, the semicircular canal of the blue whale—an animal that reaches lengths of 100 feet—is about the same size as the human semicircular canal (Stokstad 2003). Scientists hypothesize that the “shrinking” of the semicircular canal in cetaceans allows them to perform highly acrobatic maneuvers underwater without losing their balance. In humans, the equivalent movements make us dizzy and/or sick. The lower jaw of cetaceans—at least the toothed ones—also functions in hearing by acting as a conduit or channel for ultrasonic, high frequency sounds used in echolocation (e.g. Aroyan 2001). The use of the lower jaw in sound reception, called mandibular hearing, is not unique to cetaceans but may be used by other vertebrates as well.

A number of physiological adaptations also accompanied the evolution of cetaceans into the ocean, including salt-and-water balance or osmoregulation. Osmoregulation concerns the proper maintenance of salts and water in the body and involves a number of processes, including loss of water through breathing, sweating, urination, defecation, crying (lacrimation) or lactation and gaining of water and salts through drinking or eating. In cetaceans, it appears that the primary means by which they maintain water balance is through diet and metabolic production of water in digestion (Ortiz 2001) but by no means are studies conclusive or comprehensive for all cetaceans. Physiological measurements on large animals who live underwater are understandably difficult. Although scientists are uncertain how cetaceans osmoregulate, they can from the fossil record determine at what stage in their evolution osmoregulation became important. Because freshwater and saltwater differ in their oxygen isotope ratios, scientists hypothesized that the bones of fossil cetaceans may hold clues regarding the source of water ingested by these animals. An analysis of the oxygen isotope ratios of the teeth of several cetacean fossils revealed the timing and transition of these animals to a marine environment in the middle Eocene (e.g. Roe et al., 1998). The application of stable isotopes to understanding the physiology of ancient marine organisms provides an additional tool for understanding the evolution of these animals, their diets and the climate in which they lived (e.g. Kohn 1996).

Thermoregulation in cetaceans involves a rete mirabilia system similar to that we discussed for tuna and other scromboid fishes. These countercurrent heat exchangers (CCHE) conserve heat with a network of thin-walled veins surrounding arteries such that cooler venus blood from the animal’s periphery is warmed by the arterial blood. The CCHE also function to cool the temperature-sensitive reproductive organs of the animals which have evolved to their internal position presumably in response to selective pressure for streamlining. The male testes of cetaceans—wedged between the locomotor muscles of the animal where may they experience overheating—require cooling to prevent overheating and maintain sperm production. The CCHE becomes particularly important for animals who remain submerged for long periods of time, like the sperm whale. The CCHE of sperm whales is one of the most highly developed of all cetaceans with rete mirabilia around the brain, spinal cord and nervous systems, as well as the spermaceti organ, which is thought to function in echolocation (Melnikov 1997).

A provocative hypothesis concerning the evolution of the CCHE in testicular cooling poses that this feature represents an arrested embryonic state, i.e. during development the testicles are prevented from descending in the manner typical of most mammals. The retention of embryonic or juvenile characteristics in adults is known as paedomorphosis, a type of development that may explain the evolution of certain adaptations in organisms (e.g. Pabst et al., 1998). Studies of gene regulatory processes in the embryogenesis and development promise to advance considerably our understanding of the mechanisms leading to adaptive radiation and evolution (e.g. Thewissen and Williams 2002). Identification of the genes responsible for the loss of pelvic fins in sticklebacks—a marine goby-like fish—provide one example (Shapiro et al. 2004).

Of course, cetaceans also maintain a high degree of insulating blubber whose lipid composition varies within and among species. These differences in blubber types led to preferential selection of some species over others by whalers. The lipid content of blubber determines the thermal conductivity of the animal: more heat is retained when the lipid concentration is higher. Thus, tropical species tend to have thinner blubber with a lower lipid concentration than temperate and cold-water species. Dolphins (and probably other cetaceans) may gain or lose blubber in response to colder or warmer conditions (see Berta and Sumich 1999 for further discussion).

Transformation of a land-based mammal to an aquatic one also demanded greater brain-power. The cetacean brain is second only to humans in degree of encephalization—a measure of the size of the brain versus the weight of the animal. Cetacean brains exhibit considerable differences from other mammals, including reduction of the olfactory and limbic lobes, as might be expected and enlargement of brain regions involved in auditory functions and enlargement and elaboration of the neocortex, involved in cognitive and behavioral activities. Given the diverse and advanced behaviors of dolphins, it may not be surprising that they exhibit highly developed brains. However, it is not as apparent what caused the development of such highly a highly sophisticated brain. To answer that, we must look at the environment in which cetaceans evolved and speculate on the selective pressures that may have shaped their evolution.

Note 1: Many aspects of evolution remain controversial, even among scientists, yet the occurrence of evolution on our planet is indisputable, at least among rational-minded people. An excellent overview of evolution and the evidence that supports it can be found at the Talk Origins web site, http://www.talkorigins.org/. See especially their FAQ.

Note 2: Many textbooks, web sites, and documentaries continue to promote the “wolf-ancestor” theory for the evolution of whales, an idea that appears rejected. However, as additional cetacean fossils are found and more complete genomic sequences are compared, the phylogenetic relationships among cetaceans may change. It is always advisable to check your sources and draw conclusions based on multiple authors, present company included.

Note 3: An excellent overview of the evolution of the jaw in vertebrates and its relationship to the development of the inner ear of mammals can be found in Gould’s Dinosaur in a Haystack (1995).