Why Study Fossils? thie hps catered times among ver ebrates. Birds and but pterosaurs, I grew up on the streets of New York City, such as the one in a family of modest means and little for- pictured,became mal education, but with a deep love of extinct with the di learning. Like many urban kids who be- nosaurs about 65 come naturalists, my inspiration came million years ago from a great museum-in particular, fre the magnificent dinosaurs on display at the American Museum of Natural History. As we all know from Jurassic Park and other urces,dinomania in young children (I was five when I saw my first dinosaur)is not rare-but nearly all children lose the Stephen Jay Gould passion, and the desire to become a pale Harvard University ontologist becomes a transient moment between policeman and fireman in a chro- nology of intended professions. But I per- geological time, occur by a natural process by studying modern organisms. But history sisted and became a professional paleontol- of evolutionary transformation-"descent is complex and unpredictable--and prine ogist, a student of life's history as revealed with modification, "in Darwins words. I ples of evolution(like natural selection) by the evidence of fossils(though I ended was thrilled to learn that humans had arisen cannot specify the pathway that life's histo- up working on snails rather than dino- from apelike ancestors, who had themselves ry has actually followed. Paleontology holds saurs. ). Why? evolved from the tiny mouselike mammals the archives of the pathway-the fossil I remained committed to paleontology that had lived in the time of dinosaurs and record of past life, with its fascinating histo- because I discovered, still as a child, the seemed then so inconspicuous, so unsuc- ry of mass extinctions, periods of rapi onder of one of the greatest transforming cessful, and so unpromising change, long episodes of stability, and con- ideas ever discovered by science: evolution. Now, at mid-career (I was born in 1941) stantly changing patterns of dominance and I learned that those dinosaurs, and all crea- I remain convinced that I made the right diversity. Humans represent just one tiny, tures that have ever lived, are bound to- choice, and committed to learn and convey, largely fortuitous, and late-arising twig on gether in a grand family tree of physical re- as much as I can as long as I can, about evo- the enormously arborescent bush of life changes of life, through billions of years in a great deal about the process of evolution all bushes y is the study of this grandest of Molecular Biology can even estimate the rates at which evolution is occurring Biochemical tools are now of major importance in efforts to in different groups of organisms reach a better understanding of how evolution occurs Within the last few years, for example, evolutionary biolo- Development gists have begun to"read"genes, much as you are reading Twentieth-century knowledge about growth and develop- this page. They have learned to recognize the order of the letters"of the long DNA molecules, which are present in ment further supports Darwin,s theory of evolution. Strik every living cell and which provide the genetic information ing similarities are seen in the developmental stages of nany organisms of different species. Human embryos, for for that organism. By comparing the sequences of"letters" example, go through a stage in which they possess the the dNA of different groups of animals or plants, we can same structures that give rise to the gills in fish, a tail, and specify the degree of relationship among the grou detailed ment of an organism (its ontogeny)often yields informa- more even a stage when the embryo has fur! Thus, the develop- family trees can then be constructed. The consistent pattern on about the evolutionary history of the species as a emerging from a growing mountain of data is one of pro- whole (its phylogeny) species showing more differences in their DNa than closely related ones, just as Darwin's theory predicts. By measuring Since darwin's time. new discoveries of the fossil the degree of difference in the genetic coding, and by inter- record, genetics, anatomy, and development all support preting the information available from the fossil record, we Darwin's theory 16 Part I The Origin of living things
Molecular Biology Biochemical tools are now of major importance in efforts to reach a better understanding of how evolution occurs. Within the last few years, for example, evolutionary biologists have begun to “read” genes, much as you are reading this page. They have learned to recognize the order of the “letters” of the long DNA molecules, which are present in every living cell and which provide the genetic information for that organism. By comparing the sequences of “letters” in the DNA of different groups of animals or plants, we can specify the degree of relationship among the groups more precisely than by any other means. In many cases, detailed family trees can then be constructed. The consistent pattern emerging from a growing mountain of data is one of progressive change over time, with more distantly related species showing more differences in their DNA than closely related ones, just as Darwin’s theory predicts. By measuring the degree of difference in the genetic coding, and by interpreting the information available from the fossil record, we can even estimate the rates at which evolution is occurring in different groups of organisms. Development Twentieth-century knowledge about growth and development further supports Darwin’s theory of evolution. Striking similarities are seen in the developmental stages of many organisms of different species. Human embryos, for example, go through a stage in which they possess the same structures that give rise to the gills in fish, a tail, and even a stage when the embryo has fur! Thus, the development of an organism (its ontogeny) often yields information about the evolutionary history of the species as a whole (its phylogeny). Since Darwin’s time, new discoveries of the fossil record, genetics, anatomy, and development all support Darwin’s theory. 16 Part I The Origin of Living Things by studying modern organisms. But history is complex and unpredictable—and principles of evolution (like natural selection) cannot specify the pathway that life’s history has actually followed. Paleontology holds the archives of the pathway—the fossil record of past life, with its fascinating history of mass extinctions, periods of rapid change, long episodes of stability, and constantly changing patterns of dominance and diversity. Humans represent just one tiny, largely fortuitous, and late-arising twig on the enormously arborescent bush of life. Paleontology is the study of this grandest of all bushes. geological time, occur by a natural process of evolutionary transformation—“descent with modification,” in Darwin’s words. I was thrilled to learn that humans had arisen from apelike ancestors, who had themselves evolved from the tiny mouselike mammals that had lived in the time of dinosaurs and seemed then so inconspicuous, so unsuccessful, and so unpromising. Now, at mid-career (I was born in 1941) I remain convinced that I made the right choice, and committed to learn and convey, as much as I can as long as I can, about evolution and the history of life. We can learn a great deal about the process of evolution I grew up on the streets of New York City, in a family of modest means and little formal education, but with a deep love of learning. Like many urban kids who become naturalists, my inspiration came from a great museum—in particular, from the magnificent dinosaurs on display at the American Museum of Natural History. As we all know from Jurassic Park and other sources, dinomania in young children (I was five when I saw my first dinosaur) is not rare—but nearly all children lose the passion, and the desire to become a paleontologist becomes a transient moment between policeman and fireman in a chronology of intended professions. But I persisted and became a professional paleontologist, a student of life’s history as revealed by the evidence of fossils (though I ended up working on snails rather than dinosaurs!). Why? I remained committed to paleontology because I discovered, still as a child, the wonder of one of the greatest transforming ideas ever discovered by science: evolution. I learned that those dinosaurs, and all creatures that have ever lived, are bound together in a grand family tree of physical relationships, and that the rich and fascinating changes of life, through billions of years in Why Study Fossils? Flight has evolved three separate times among vertebrates. Birds and bats are still with us, but pterosaurs, such as the one pictured, became extinct with the dinosaurs about 65 million years ago. Stephen Jay Gould Harvard University
1. 4 This book is organized to help you learn biology Core Principles you will examine evolution, the gradual change in popula of biolog tions from one generation to the next, which has led through natural selection to the biological diversity we see around us. Finally, at the community and ecosystem levels organizing principle has emerged: biological diversity re- you will study ecology, which deals with how organisms in- flects history, a record of success, failure, and change ex- teract with their environments and with one another to pro- tending back to a period soon after the formation of the earth. The explanation for this diversity, the theory of evo- earth lution by natural selection, will form the backbone of your study of biological science, just as the theory of the covalent Organisms bond is the backbone of chemistry, or the theory of quan- The second half of the book is devoted to an examination of that of tion is a thread that runs through everything you will learn organisms, the products of evolution. It is estimated that at in this book. east 5 million different kinds of plants, animals, and micro- organisms exist, and their diversity is incredible(figure 1. 13) Later in the book, we will take a particularly detailed look at Basic principles the vertebrates, the group of animals of which we are mem- The first half of this book is devoted to a description of the bers. We will consider the vertebrate body and how it func- basic principles of biology, introduced through a levels-of- tions, as this information is of greatest interest and impor organization framework(see figure 1.2). At the molecular, tance to most students troduced to cell biology. You will learn how cells are con- structed and how they grow, divide, and communicate.At As you proceed through this book, what you learn at one the organismal level, you will learn the principles of genetics, stage will give you the tools to understand the next. The hich deal with the way that individual traits are transmit core principle of biology is that biological diversity is the ted from one generation to the next. At the population level, esult of a long evolutionary journe Plantae Animalia Eubacteria FIGURE 1.13 The diversity of life. Biologists categorize all living things into six major groups called kingdoms: archaebacteria, Archaebacteria eubacteria, protists, fungi, pla Chapter 1 The Science of Biology 17
Chapter 1 The Science of Biology 17 Core Principles of Biology From centuries of biological observation and inquiry, one organizing principle has emerged: biological diversity reflects history, a record of success, failure, and change extending back to a period soon after the formation of the earth. The explanation for this diversity, the theory of evolution by natural selection, will form the backbone of your study of biological science, just as the theory of the covalent bond is the backbone of chemistry, or the theory of quantum mechanics is that of physics. Evolution by natural selection is a thread that runs through everything you will learn in this book. Basic Principles The first half of this book is devoted to a description of the basic principles of biology, introduced through a levels-oforganization framework (see figure 1.2). At the molecular, organellar, and cellular levels of organization, you will be introduced to cell biology. You will learn how cells are constructed and how they grow, divide, and communicate. At the organismal level, you will learn the principles of genetics, which deal with the way that individual traits are transmitted from one generation to the next. At the population level, you will examine evolution, the gradual change in populations from one generation to the next, which has led through natural selection to the biological diversity we see around us. Finally, at the community and ecosystem levels, you will study ecology, which deals with how organisms interact with their environments and with one another to produce the complex communities characteristic of life on earth. Organisms The second half of the book is devoted to an examination of organisms, the products of evolution. It is estimated that at least 5 million different kinds of plants, animals, and microorganisms exist, and their diversity is incredible (figure 1.13). Later in the book, we will take a particularly detailed look at the vertebrates, the group of animals of which we are members. We will consider the vertebrate body and how it functions, as this information is of greatest interest and importance to most students. As you proceed through this book, what you learn at one stage will give you the tools to understand the next. The core principle of biology is that biological diversity is the result of a long evolutionary journey. 1.4 This book is organized to help you learn biology. Plantae Animalia Fungi Eubacteria Archaebacteria Protista FIGURE 1.13 The diversity of life. Biologists categorize all living things into six major groups called kingdoms: archaebacteria, eubacteria, protists, fungi, plants, and animals
Chapter 1 http://www.mhhe.com/raven6ehttp://www.biocourse.com Questions Media resource 1.1 Biology is the science of life Living things are highly organized, whether as single 1. What are the characteristics Art Activity: Biological cells or as multicellular organisms, with several hie archical levels 1.2 Scientists form generalizations from observations Science is the determination of general principles 2. What is the difference be- Scientists on science from observation and tween deductive and inductive Why Paleontology Scientists select the best hypotheses by using easoning? What is a hypothesis? controlled experiments to eliminate alternative 3. What are variables? How are Probability and Hypothesis Testing in hypotheses that are inconsistent with observations control experiments used in test ing hypotheses a group of related hypotheses supported by a large body of evidence is called a theory. In science, a 4. How does a hypothesis theory represents what we are most sure about become a theory? At what point does a theory become accepted However, there are no absolute truths in science, and as an absolute truth, no longer even theories are accepted only conditionally subject to any uncertainty? Scientists conduct basic research, designed to gair 5. What is the difference nformation about natural phenomena in order to tween basic and a contribute to our overall body of knowledge, and research applied research, devoted Solv g specific problem th cations 1.3 Darwins theory of evolution illustrates how science works. One of the central theories of biology is Darwins 6. Describe the evidence that le theory that evolution occurs by natural selection. It Darwin to propose that evolu- ution states that certain individuals have heritable traits that tion occurs by means of natural Before dar allow them to produce more offspring in a given kind selection. What evidence Voyage of the Beagle of environment than other individuals lacking those gathered since the publication of The Process of Natural traits. Consequently, those traits will increase in Darwins theory has lent further Selection frequency through time support to the theory? Evidence for evolution 7. What is the difference be- Because environments differ in their requirements tween homologous and analo- it Research: The and opportunities, the traits favored by natural gous structures:Give an for medicinal election will vary in different environments. example of each This theory is supported by a wealth of evidence ac- 140 Years Without quired over more than a century of testing and Bird-Killing ca Making Better Bids 1. 4 This book is organized to help you learn biolog Biological diversity is the result of a long history of 8. Can you think of any alterna- evolutionary change. For this reason evolution is the tives to levels-of-organization as core of the science of bole ways of organizing the mass of Considered in terms of levels-of-organization, the information in biology cience of biology can be said to consist of subdisci- lines focusing on particular levels. Thus one speaks of molecular biology, cell biology, organismal biolo- gy, population biology, and community biology 18 Part I The Origin of Living Things
Chapter 1 Summary Questions Media Resources 1.1 Biology is the science of life. 18 Part I The Origin of Living Things • Living things are highly organized, whether as single cells or as multicellular organisms, with several hierarchical levels. 1. What are the characteristics of living things? 1.2 Scientists form generalizations from observations. • Science is the determination of general principles from observation and experimentation. • Scientists select the best hypotheses by using controlled experiments to eliminate alternative hypotheses that are inconsistent with observations. • A group of related hypotheses supported by a large body of evidence is called a theory. In science, a theory represents what we are most sure about. However, there are no absolute truths in science, and even theories are accepted only conditionally. • Scientists conduct basic research, designed to gain information about natural phenomena in order to contribute to our overall body of knowledge, and applied research, devoted to solving specific problems with practical applications. 2. What is the difference between deductive and inductive reasoning? What is a hypothesis? 3. What are variables? How are control experiments used in testing hypotheses? 4. How does a hypothesis become a theory? At what point does a theory become accepted as an absolute truth, no longer subject to any uncertainty? 5. What is the difference between basic and applied research? 6. Describe the evidence that led Darwin to propose that evolution occurs by means of natural selection. What evidence gathered since the publication of Darwin’s theory has lent further support to the theory? 7. What is the difference between homologous and analogous structures? Give an example of each. 8. Can you think of any alternatives to levels-of-organization as ways of organizing the mass of information in biology? • One of the central theories of biology is Darwin’s theory that evolution occurs by natural selection. It states that certain individuals have heritable traits that allow them to produce more offspring in a given kind of environment than other individuals lacking those traits. Consequently, those traits will increase in frequency through time. • Because environments differ in their requirements and opportunities, the traits favored by natural selection will vary in different environments. • This theory is supported by a wealth of evidence acquired over more than a century of testing and questioning. • Biological diversity is the result of a long history of evolutionary change. For this reason evolution is the core of the science of biology. • Considered in terms of levels-of-organization, the science of biology can be said to consist of subdisciplines focusing on particular levels. Thus one speaks of molecular biology, cell biology, organismal biology, population biology, and community biology. 1.3 Darwin’s theory of evolution illustrates how science works. 1.4 This book is organized to help you learn biology. • Art Activity: Biological organization • Scientists on Science: Why Paleonthology? • Experiments: Probability and Hypothesis Testing in Biology • Introduction to Evolution • Before Darwin • Voyage of the Beagle • Natural Selection • The Process of Natural Selection • Evidence for Evolution • Student Research: The Search for Medicinal Plants on Science Articles • 140 Years Without Darwin Are Enough • Bird-Killing Cats: Nature’s Way of Making Better Bids http://www.mhhe.com/raven6e http://www.biocourse.com
The nature of M olecules Concept Outline 2.1 Atoms are nature's building material Atoms. All substances are composed of tiny particles called toms, each a positively charged nucleus around which orbit negatve Electrons determine the Chemical behavior of atoms Electrons orbit the nucleus of an atom: the closer electron' s orbit to the nucleus. the lowe 2.2 The atoms of living things are among the smallest Kinds of Atoms. Of the 92 naturally occurring element only 11 occur in organisms in significant amounts 2. 3 Chemical bonds hold molecules together. Ionic Bonds Form Crystals. Atoms are linked together into molecules, joined by chemical bonds that result from forces like the attraction of opposite charges or the sharing of electrons Covalent Bonds build Stable molecules. Chemical bonds formed by the sharing of electrons can be very strong, FIGURE 2.1 and require much energy to break. Cells are made of molecules. Specific, often simple, combina tions of atoms yield an astonishing diversity of molecules within 2.4 Water is the cradle of life the cell, each with unique functional characteristics. Chemistry of Water. Water forms weak chemical associations that are responsible for much of the organization of living chemistry. Water Atoms Act Like Tiny Magnets. Because electrons bout 10 to 20 billion years ago, an enormous explo- are shared unequally by the hydrogen and oxygen atoms of sion likely marked the beginning of the universe water, a partial charge separation occurs. Each water atom With this explosion began the process of evolution, which acquires a positive and negative pole and is said to be"polar. eventually led to the origin and div versification of life on Water Clings to Polar Molecules. Because the opposite earth. When viewed from the perspective of 20 billion of polar molecules attract one another, water tends to cling to itself and other polar molecules and to years, life within our solar system is a recent development, exclude nonpolar molecules but to understand the origin of life, we need to consider Water Ionizes. Because its covalent bonds occasionally events that took place much earlier. The same processes break, water contains a low concentration of hydrogen(H+) hat led to the evolution of life were responsible for the Ind hydroxide(OH-)ions, the fragments of broken water evolution of molecules(figure 2.1). Thus, our study of life on earth begins with physics and chemistry. As chemical machines ourselves, we must understand chemistry to
19 2 The Nature of Molecules Concept Outline 2.1 Atoms are nature’s building material. Atoms. All substances are composed of tiny particles called atoms, each a positively charged nucleus around which orbit negative electrons. Electrons Determine the Chemical Behavior of Atoms. Electrons orbit the nucleus of an atom; the closer an electron’s orbit to the nucleus, the lower its energy level. 2.2 The atoms of living things are among the smallest. Kinds of Atoms. Of the 92 naturally occurring elements, only 11 occur in organisms in significant amounts. 2.3 Chemical bonds hold molecules together. Ionic Bonds Form Crystals. Atoms are linked together into molecules, joined by chemical bonds that result from forces like the attraction of opposite charges or the sharing of electrons. Covalent Bonds Build Stable Molecules. Chemical bonds formed by the sharing of electrons can be very strong, and require much energy to break. 2.4 Water is the cradle of life. Chemistry of Water. Water forms weak chemical associations that are responsible for much of the organization of living chemistry. Water Atoms Act Like Tiny Magnets. Because electrons are shared unequally by the hydrogen and oxygen atoms of water, a partial charge separation occurs. Each water atom acquires a positive and negative pole and is said to be “polar.” Water Clings to Polar Molecules. Because the opposite partial charges of polar molecules attract one another, water tends to cling to itself and other polar molecules and to exclude nonpolar molecules. Water Ionizes. Because its covalent bonds occasionally break, water contains a low concentration of hydrogen (H+) and hydroxide (OH–) ions, the fragments of broken water molecules. About 10 to 20 billion years ago, an enormous explosion likely marked the beginning of the universe. With this explosion began the process of evolution, which eventually led to the origin and diversification of life on earth. When viewed from the perspective of 20 billion years, life within our solar system is a recent development, but to understand the origin of life, we need to consider events that took place much earlier. The same processes that led to the evolution of life were responsible for the evolution of molecules (figure 2.1). Thus, our study of life on earth begins with physics and chemistry. As chemical machines ourselves, we must understand chemistry to begin to understand our origins. FIGURE 2.1 Cells are made of molecules. Specific, often simple, combinations of atoms yield an astonishing diversity of molecules within the cell, each with unique functional characteristics
2.1 Atoms are nature's building material. Atoms Any substance in the universe that has ass(see below)and occupies space defined as matter. All matter is com- osed of extremely small particles called atoms. Because of their siz atoms are difficult to study. Not until early in this century did scientists carry out the first experiments sug gesting what an atom is like. The Structure of atoms Objects as small as atoms can be “seen” only indirectly, by using very complex technology such as tunneling microcopy. We now know a great Oxyge deal about the complexities of atomic structure,but the simple view put 8 Neutrons forth in 1913 by the Danish physicist Niels Bohr provides a good starting point. Bohr proposed that every atom assesses an orbiting cloud of subatomic particles called electrons hizzing around a core like the plan- ets of a miniature solar system. At the Proton o Neutron Electron o center of each atom is a small,very dense nucleus formed of two other ve charge (No charge) (Negative charge) kinds of subatomic particles, protons FIGURE 2.2 Within the nucleus, the cluster of Basic structure of atoms. All atoms have a nucleus consisting of protons and neutrons, cept hydrogen, the smallest atom, which has only one proton and no neutrons in its protons and neutrons is held together nucleus. Oxygen, for example, has eight protons and eight neutrons in its nucleus. Electrons by a force that works only over short spin around the nucleus a far distance away from the nucleus subatomic distances. Each proton car- a positive (+) charge, and each electron carries a negative(-)ch Typically an atom has one electron for each proton. The number of protons(the atoms weigbt will be greater on the earth because the earths grav atomic number) determines the chemical character of the itational force is greater than the moons. The atomic atom,because it dictates the number of electrons orbiting mass of an atom is equal to the sum of the masses of its the nucleus which are available for chemical activity. Neu rotons and neutrons. Atoms that occur naturally on earth trons, as their name implies, possess no charge contain from 1 to 92 protons and up to 146 neutrons The mass of atoms and subatomic particles is measured Atomic mass in units called daltons. To give you an idea of just how small these units are. note that it takes 602 million million billion The terms mass and weight are often used interchangeably, (6.02 x 102)daltons to make 1 gram! A proton weighs ap- but they have slightly different meanings. Mass refers to the proximately 1 dalton(actually 1.009 daltons), as does a neu amount of a substance, while weigbt refers to the force tron(1.007 daltons). In contrast, electrons weigh only 18o of gravity exerts on a substance. Hence, an object has the a dalton, so their contribution to the overall mass of an atom same mass whether it is on the earth or the moon, but its is negligible. 20 Part i The Origin of Living things
weight will be greater on the earth because the earth’s gravitational force is greater than the moon’s. The atomic mass of an atom is equal to the sum of the masses of its protons and neutrons. Atoms that occur naturally on earth contain from 1 to 92 protons and up to 146 neutrons. The mass of atoms and subatomic particles is measured in units called daltons. To give you an idea of just how small these units are, note that it takes 602 million million billion (6.02 × 1023) daltons to make 1 gram! A proton weighs approximately 1 dalton (actually 1.009 daltons), as does a neutron (1.007 daltons). In contrast, electrons weigh only 1 1840 of a dalton, so their contribution to the overall mass of an atom is negligible. 20 Part I The Origin of Living Things Atoms Any substance in the universe that has mass (see below) and occupies space is defined as matter. All matter is composed of extremely small particles called atoms. Because of their size, atoms are difficult to study. Not until early in this century did scientists carry out the first experiments suggesting what an atom is like. The Structure of Atoms Objects as small as atoms can be “seen” only indirectly, by using very complex technology such as tunneling microcopy. We now know a great deal about the complexities of atomic structure, but the simple view put forth in 1913 by the Danish physicist Niels Bohr provides a good starting point. Bohr proposed that every atom possesses an orbiting cloud of tiny subatomic particles called electrons whizzing around a core like the planets of a miniature solar system. At the center of each atom is a small, very dense nucleus formed of two other kinds of subatomic particles, protons and neutrons (figure 2.2). Within the nucleus, the cluster of protons and neutrons is held together by a force that works only over short subatomic distances. Each proton carries a positive (+) charge, and each electron carries a negative (–) charge. Typically an atom has one electron for each proton. The number of protons (the atom’s atomic number) determines the chemical character of the atom, because it dictates the number of electrons orbiting the nucleus which are available for chemical activity. Neutrons, as their name implies, possess no charge. Atomic Mass The terms mass and weight are often used interchangeably, but they have slightly different meanings. Mass refers to the amount of a substance, while weight refers to the force gravity exerts on a substance. Hence, an object has the same mass whether it is on the earth or the moon, but its 2.1 Atoms are nature’s building material. FIGURE 2.2 Basic structure of atoms. All atoms have a nucleus consisting of protons and neutrons, except hydrogen, the smallest atom, which has only one proton and no neutrons in its nucleus. Oxygen, for example, has eight protons and eight neutrons in its nucleus. Electrons spin around the nucleus a far distance away from the nucleus. Proton (Positive charge) (No charge) (Negative charge) Neutron Electron Hydrogen 1 Proton 1 Electron Oxygen 8 Protons 8 Neutrons 8 Electrons