Biological Principles and the Science of Zoology

PART ONE CHAPTER Life: Biological Principles and the Science of Zoology Zoologist studying the behavior of yellow baboons (Papio cynocephalus) in the Amboseli Reserve, Kenya. The Uses of Principles We explore the animal world by actively applying important principles come from previous studies of the living world, of guiding principles to our investigations. Just as the exploration which animals are one part. of outer space is both guided and limited by available technolo- Principles of heredity, variation, and organic evolution guide gies, exploration of the animal world depends critically on our the study of life from the simplest unicellular forms to the most questions, methods, and principles. The body of knowledge that complex animals, fungi, and plants. Because life shares a common we call zoology makes sense only when the principles that we evolutionary origin, principles learned from the study of one group use to construct it are understood. often provide insights into other groups as well. By tracing the The principles of modern zoology trace their long history origins of our operating principles, we see that zoologists are not to many sources. Some principles come from laws of physics an island unto themselves but part of a larger scientific community. and chemistry, which all living systems obey. Others come We begin our study of zoology by searching broadly for our from the scientific method, which tells us that our hypothetical most basic principles and their diverse sources. These principles explanations of the animal world must guide us to gather data simultaneously guide our studies of animals and integrate those that potentially can refute these explanations. Many important studies into the broader context of human knowledge. PART ONE Introduction to Living Animals oology, the scientific study of animal life, builds on centu- a systematic way. This complex and exciting process builds on the ries of human observations of the animal world. Mytholo- contributions of thousands of zoologists working in all dimensions Zgies of nearly eveiy human culture reveal early attempts of the biosphere (Figure 1.1). We strive to explain how animal to solve the mysteries of animal life and its origin. Zoologists diversity originated and how animals perform the basic processes of now confront these same mysteries with the most advanced life that permit them to inhabit diverse environments. methods and technologies developed by all branches of sci- This chapter introduces the fundamental properties of ani- ence. We document the diversity of animal life and organize it in mal life, the methodological principles that govern their study, B l.i A few of the many dimensions of zoological research. A, Observing moray eels in Maui, Hawaii. B, Working with tranquilized polar bears. C, Banding mallard ducks. D, Observing Daphnia pulex (x150) microscopically. E, Separating growth stages of crab larvae at a marine laboratory. www.mhhe.com/hickrnanipzl5e CHAPTER I Life: Biological Principles and the Science of Zoology and two important theories that guide our research: (1) the among living forms. These properties, reviewed in the next theory of evolution, which is the central organizing principle of section, clearly identify their possessors as part of the unified biology, and (2) the chromosomal theory of inheritance, which historical entity called life. All such features characterize the explains heredity and variation in animals. These theories unify most highly evolved forms of life, such as those that compose our knowledge of the animal world. the animal kingdom. Because they are so important for mainte- nance and functioning of living forms that possess them, these properties persist through life's evolutionary history. FUNDAMENTAL PROPERTIES OF LIFE Does Life Have Defining Properties? General Properties of Living Systems Life's most outstanding general features include chemical unique- We begin with the difficult question, What is life? Although ness; complexity and hierarchical organization; reproduction many scientists have tried to define life, simple definitions are (heredity and variation); possession of a genetic program; metab- doomed to failure. When we try to give life a simple definition, olism; development; environmental interaction; and movement. we look for fixed properties that separate living from nonliving matter. However, the properties that life exhibits today 1. Chemical uniqueness. Living systems demonstrate a (pp. 3-8) are very different from those of the earliest living unique and complex molecular organization. Living sys- forms. The history of life shows extensive and ongoing change, tems assemble large molecules, called macromolecules, which we call evolution. As the genealogy of life progressed and that are far more complex than the small molecules of branched from the original living form to the millions of species nonliving matter. Assembly of macromolecules uses the alive today, new properties evolved and passed from parents to same kinds of atoms and chemical bonds that occur their offspring. Through this process, living systems have gener- in nonliving matter and obeys all fundamental laws of ated many spectacular features that have no counterparts in the chemistry; it is only the complex organizational structure nonliving world. Unexpected properties emerge on many dif- of these macromolecules that makes them unique. We ferent lineages in life's evolutionary history, producing the great recognize four major categories of biological macromol- organismal diversity observed today. ecules: nucleic acids, proteins, carbohydrates, and lipids We could try to define life by universal properties evident at (see Chapter 2). These categories differ in the structures its origin. Replication of molecules, for example, traces to life's of their component parts, the kinds of chemical bonds origin and is one of life's universal properties. Defining life in that link their subunits together, and their functions in this manner faces the major/problem that these are the proper- living systems. ties most likely to be shared by some nonliving forms. To study The general structures of these macromolecules evolved the origin of life, we must ask how organic molecules acquired and stabilized early in the history of life. With some modi- an ability for precise replication. But where do we draw the line fications, these same general structures occur in eveiy form between those replicative processes that characterize life and of life today. Proteins, for example, are built from 20 specific those that are merely general chemical reactions of the matter kinds of amino acid subunits linked together by peptide from which life arose? Replication of complex crystalline struc- bonds in a linear sequence (Figure 1.2). Additional bonds tures in nonliving chemical assemblages might be confused, for occurring between amino acids that are not adjacent to each example, with the replicative molecular properties associated other in the protein chain give the protein a complex, three- with life. If we define life using only the most advanced char- dimensional structure (see Figures 1.2 and 2.15). A typical acteristics of the highly evolved living systems observed today, protein contains several hundred amino acid subunits. De- the nonliving world would not intrude on our definition, but spite the stability of this basic protein structure, the ordering we would eliminate the early forms of life from which all others of the different amino acids in a protein molecule shows descended and which give life its historical unity. enormous variation. This variation underlies much of the Ultimately our definition of life must be based on the com- diversity that we observe among different kinds of living mon history of life on earth. Life's history of descent with modi- organisms. The nucleic acids, carbohydrates, and lipids like- fication gives it an identity and continuity that separates it from wise contain characteristic bonds that link variable sub- the nonliving world. We trace this common history backward units (see Chapter 2). This organization gives living systems through time from the diverse forms observed today and in the a common biochemical theme with great potential diversity. fossil record to their common ancestor that arose almost 5 billion 2. Complexity and hierarchical organization. Living years ago (see Chapter 2). All organisms forming part of this long systems demonstrate a unique and complex hierarchi- history of hereditary descent from life's common ancestor lie within cal organization. Nonliving matter is organized at least our concept of life. into atoms and molecules and often has a higher degree Although we cannot force life into a simple definition, we of organization as well. However, atoms and molecules can readily identify the living world through its history of com- are combined into patterns in the living world that do mon evolutionary descent. Many remarkable properties have not exist in nonliving matter. In living systems, we find arisen during life's history and appear in various combinations a hierarchy of levels that includes, in ascending order PART ONE Introduction to Living Animals Amino acid Amino acid • Amino acid B Figure 1.2 A computer simulation of the three-dimensional structure of the lysozyme protein (A), which is used by animals to destroy bacteria. The protein is a linear string of molecular subunits called amino acids, connected as shown in B, which fold in a three-dimensional pattern to form

Load more