CONTENTS. Introduction 10

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2 CONTENTS Introduction 10 Chapter 1: understanding Evolution 19 The Evidence for Evolution 21 The Fossil Record 22 Structural Similarities 27 Embryonic Development and Vestiges 28 Biogeography 29 Molecular Biology 31 History of Evolutionary Theory 34 Early Ideas 34 Charles Darwin 37 Lamarckism 38 Modern Conceptions 41 Sir Joseph Dalton Hooker 42 The Cultural Impact of Evolutionary Theory 53 Scientific Acceptance and Extension to Other Disciplines 53 Religious Criticism and Acceptance 58 Intelligent Design and Its Critics 64 Chapter 2: the Process of Evolution 72 Evolution as a Genetic Function 72 Genetic Variation in Populations 74 The Origin of Genetic Variation: Mutations 79 Industrial Melanism 80 The Dynamics of Genetic Change 87 Genetic Equilibrium: The Hardy-Weinberg Law 87 The Processes of Gene-Frequency Change

3 The Operation of Natural Selection in Populations 95 Natural Selection as a Process of Genetic Change 95 Analogy 105 Homology 106 Types of Selection 108 Chapter 3: species and speciation 121 The Origin of Species 123 Reproductive Isolation 124 A Model of Speciation 129 Geographic Speciation 132 Adaptive Radiation 135 Quantum Speciation 138 Polyploidy 139 Genetic Differentiation During Speciation 141 Patterns and Rates of Species Evolution 145 Evolution Within a Lineage and by Lineage Splitting 146 Convergent and Parallel Evolution 148 Gradual and Punctuational Evolution 152 Diversity and Extinction 158 Evolution and Development 162 Chapter 4: Reconstruction of Evolutionary history 166 DNA and Protein as Informational Macromolecules 167 Evolutionary Trees 169 Distance Methods 170 Maximum Parsimony Methods 174 Maximum Likelihood Methods 176 Evaluation of Evolutionary Trees

4 Molecular Evolution 177 Molecular Phylogeny of Genes 177 Multiplicity and Rate Heterogeneity 180 The Molecular Clock of Evolution 183 The Neutrality Theory of Molecular Evolution 186 Chapter 5: notable Evolutionary thinkers 189 Charles Darwin 189 Early Life and Education 191 The Beagle Voyage 193 Evolution by Natural Selection: The London Years, The Squire Naturalist in Downe 202 On the Origin of Species 204 The Patriarch in His Home Laboratory 208 The Private Man and the Public Debate 210 Richard Dawkins 213 Theodosius Dobzhansky 217 Sir Julian Huxley 220 T.H. Huxley 221 Student Life 222 The Rattlesnake Voyage 223 Darwin s Bulldog 225 Power and Pope Huxley 227 The Old Lion 230 Jean-Baptiste Lamarck 232 Early Life and Career 233 Professorship at the National Museum of Natural History 234 The Inheritance of Acquired Characters 235 Ernst Mayr

5 George Gaylord Simpson 239 George Ledyard Stebbins, Jr. 242 Hugo de Vries 243 Alfred Russel Wallace 244 Early Life and Work 245 The Career of a Naturalist Chapter 6: Related Evolutionary Concepts 252 Acquired Character 252 Adaptation 252 Adaptive Radiation 255 Cephalization 256 Darwinism 256 Dispersion 257 Effective Population Size 260 Emergence 260 Extinction 262 Mass Extinction Events 263 Human-Induced Extinctions 265 Kin Selection 266 Mosaic Evolution 268 Natural Selection 268 Orthogenesis 270 Parallel Evolution 270 Polymorphism 271 Selection 271 Speciation 273 Species 274 Taxonomy 275 Speciation 276 Identifying and Cataloging Species 277 Glossary 279 for further Reading 281 Index

6 INTRODUCTION INTRODUCTION

7 7 Introduction 7 I n 2009, while the world celebrated the 200th anniversary of Charles Darwin s birth, scientists announced the discovery of the oldest fossilized skeleton of an ancestral human. The significance of the timing should be clear. Darwin, the 19th-century English naturalist and author of On the Origin of the Species, argued for the theory of evolution, going so far as to provide an accurate but incomplete scientific explanation for the process. And, it was the work of Darwin and those who came after him that formed the foundation for the modern theories of evolution. Earlier scientists, such as Swedish naturalist Carolus Linnaeus, had theorized that humans and great apes were related, basing this assumption on similarities in morphology and anatomy; however, after Darwin published his theories, the scientific community began searching for a direct missing link between apes and humans. Throughout history, human cultures have tried to develop explanations for the creation of the world and the diversity of plants and animals, including humans, that populate it. The ancient Greeks, for example, proposed that animals could be transformed from one species into another, or created as an amalgamation of parts from different animals, while traditional Judaic and Christian teachings attributed the origins of the various species of plants and animals to a single, omnipotent God. By the Middle Ages, some intellectuals theorized that organisms could change over time through natural processes; however, this school of thought was not widely accepted until much later. It was during the Enlightenment of the 18th century that ideas of change and progress began to take hold. While philosophers theorized about the progress of the human mind and spirit, naturalists turned their 11

8 7 New Thinking About Evolution 7 attention to the progress of the human body. Several years before Charles Darwin was even born, intellectuals had started to advance the notion that organisms could become adapted to their environments through the modification or eradication of organs or biological structures. The French naturalist Jean-Baptiste Lamarck championed this theory of the inheritance of acquired characteristics (also known as Lamarckism). And, while this concept was disproved by the 20th century, Lamarck s ideas did lead to the gradual acceptance of the theories of biological evolution, as well as spurring on future investigation. By Darwin s time, it was understood that the world operated according to a set of natural laws. The work of individuals like Copernicus, Galileo, and Newton established that the universe was governed by the laws of science. Darwin would apply similar laws to the natural world as well. During his five-year voyage aboard the HMS Beagle, Darwin would accumulate evidence to prove that evolution had occurred, that different organisms share a common ancestor, and that organisms change over time. To account for this third assertion that organisms change over time Darwin proposed the concept of natural selection. Natural selection, according to Darwin, is the process that aids in adaptation, preserving favourable variations and rejecting injurious variations. The ramifications of Darwin s ideas became clear. In fact, it was Darwin himself who stated that his theories of natural selection would be a light thrown on the origin of man and his history. The traditional belief that humans were the creation of a divine intelligence had to be reevaluated. If, as Darwin s theory of natural selection suggests, the organisms we see every day have changed or evolved over time, is the same true of humans? Did 12

9 7 Introduction 7 modern humans emerge from a lesser-developed species? What did our earliest ancestors look like? Since the similarities between humans and apes had already been recognized, could these two groups share a common ancestor? The hunt was on for the missing link. Three years before Darwin published On the Origin of the Species, Neanderthal man was discovered in Germany and sparked the development of paleoanthropology and the study of human evolution. The idea that humans could have evolved from lesser species was not only radical, but it was controversial, as well. Even men who had supported Darwin s theory of natural selection like British naturalist Alfred Russel Wallace and Scottish geologist Charles Lyell scoffed at the idea that the human brain could have developed through the process of natural selection. However, as more and more scientists joined the search for a human ancestor, the debate soon turned from whether humans were the product of natural selection to which modern human traits emerged first. The prevailing theory at the end of the 19th and the beginning of the 20th century was that the trait that makes us most human is the modern human brain. Therefore, efforts to unearth our earliest ancestors focused on discovering a specimen with a large brain. However, as new fossilized evidence was uncovered, it became clear that our ancestors developed a modern bipedal stance before they developed an enlarged modern brain. The scientific community was outraged. They were willing to accept that modern humans were the result of Darwinian natural selection, but they couldn t accept that our ancestors developed modern bodies before modern brains. In fact, this widely held bias led to one of the most famous hoaxes in the field of human evolution: Piltdown Man. 13

10 7 New Thinking About Evolution 7 Discovered in 1912, the Piltdown Man fossils consisted of fragments of a skull and jawbone that were found by workers in a gravel pit in Piltdown, England. The fragments were brought to English amateur archaeologist Charles Dawson, who heralded the find as evidence of a human ancestor with a modern human brain. Although looked upon with some skepticism from the start, Eoanthropus dawsoni (or Dawson s dawn man ) wasn t officially exposed as a fraud until 1953, when it was revealed to consist of parts of a modern human skull and the jawbones of an orangutan. Despite being a forgery, Piltdown Man has a place in the history of human evolutionary theory as indicative of one of the largest hurdles the field had to face. Hubris made it difficult for most people whether the public or the scientific community to accept that we had evolved from ancestors who did not possess a fully developed modern brain. The second half of the 20th century provided a bounty of fossil evidence among it Lucy in 1974 and Ardi in 1994 that our ancestors developed upright bipedalism long before an increased brain. Lucy was the name given to a roughly 40 percent complete skeleton of an Australopithecus afarensis discovered in Ethiopia in Providing further evidence that bipedalism preceded brain growth, Lucy had a skull size similar to that of apes but a skeleton that had developed to allow for bipedal locomotion. Lucy would reign as one of the earliest known human ancestors for more than twenty years, when an older specimen, Ardipithecus ramidus, was discovered. Ardipithecus ramidus or Ardi was discovered, like Lucy, in the Afar desert of Ethiopia. Not only was Ardi the oldest fossil skeleton of a human ancestor, living around 4.4 million years ago, but scientists also claim that this discovery should finally put to rest the popular belief that a missing link existed that possessed traits of both humans 14

11 7 Introduction 7 and modern apes. In fact, Ardi possessed modifications in her pelvis, legs, and feet that allowed her to move through the trees in a fashion similar to species that were far more primitive than chimpanzees and gorillas. What the previous episodes prove is that the study of evolutionary theory is, itself, a constantly evolving science. When Darwin s concept of natural selection was first introduced, even its proponents lacked a suitable explanation of exactly how the favourable variations could be passed from one generation to the next. Around the time that Darwin s On the Origin of the Species was published, an Augustinian monk in Austria-Hungary was experimenting with peas in the monastery garden. The monk, Gregor Mendel, used the results of his experiments to formulate the basic principles of the theory of heredity. According to Mendel s theories, biological inheritance occurs through particulate factors that are inherited from both parents; Mendel s particulate factors would eventually become known as genes. Not to discount the contributions of individuals like Mendel, perhaps the greatest contribution to the field of evolution since Darwin s initial theories would not come until That year, American geneticist and biophysicist James Watson and British biophysicist Francis Crick published an article that described the double helix structure of DNA (or deoxyribonucleic acid), the material responsible for genetic heredity. Watson and Crick s discovery opened whole new avenues of thought regarding evolutionary biology. Now, biologists knew not only how traits were inherited through genes but also the mechanism through which these genes were passed from one generation to the next DNA. At the end of the 20th century, new techniques were developed to fully exploit science s new understanding of DNA and evolution. Biologists could now, for example, 15

12 7 New Thinking About Evolution 7 explore genetic variation on a molecular level. This new molecular understanding of evolution led to the concept of the molecular clock. According to this theory, the amount of divergence between the DNA of two different species should create a reliable estimate of when those two species diverged from a common ancestor, allowing scientists to reconstruct the evolutionary history of a species. And, while scientists have since proven that the molecular clock theory is not exact, it continues to provide fairly reliable evidence into the 21st century. Perhaps the greatest boon to the study of evolution in the 21st century is the success of the Human Genome Project. The Human Genome Project was an international project with the primary goal to determine the sequence of chemical pairs that make up DNA and to identify and map the 20,000 to 25,000 genes that make up the human genome. The project began in 1990 and, after releasing a working draft in 2000, was completed in While the stated objective of the Human Genome Project was to understand the genetic makeup of human DNA, the project has also successfully mapped the genome of more than 20 other organisms, including the rat, the mosquito, the fruit fly, and the bacterium Escherichia coli. In the decades since Darwin s work was published, scientists have all but confirmed each of Darwin s theories. Most experts agree that it is no longer accurate to call Darwin s findings theory ; they have become an accepted part of the study of biology. While Darwin may have accurately theorized the basics of evolution, modern research has shown that evolution may, in fact, work in ways that Darwin and his contemporaries could never have imagined. Although earlier naturalists stated that natural selection occurred slowly over time, modern scientists have found that evolution 16

13 7 Introduction 7 may actually occur quite rapidly. The current school of thought best explains gaps in the fossil record, which 19th-century scientists took to indicate the existence of missing links between species. Modern science, however, claims that these gaps simply indicate places where evolution took a radical leap forward. Whether it occurs quickly or slowly, scientists know one thing for certain: evolution modifies existing structures by trial and error. This is why the skeletal structures of a chimpanzee s hand, a dolphin s fin, and a bat s wing are not radically different, since they all arose from a similar structure. Similarly, despite what proponents of creation science and intelligent design may argue, the human brain, though remarkable, could not have appeared on its own and must have developed from earlier, less-developed structures. 17