Why should students be required to take a science course? The answer to this question is both complex and compelling whether you are a science major or not. Science is a human endeavor and achievement, as are art, music, and literature. While art, music, and literature suit our aesthetic needs, science and technology have successfully generated the means to satisfy our material needs. An educated person should understand the nature of science, its role in the development of our society, and something of the major scientific explanations of the natural world.
Science and scientific issues surround you. Environmental and health issues abound, ranging from AIDS, cancer, and sewage treatment to rainforest destruction, species extinctions, and global warming. The news media often report about the findings of science, but to scientists the reporting often seems inaccurate, superficial, or sensationalized. Sales pitches and advertisements tell us the results of what are held to be scientific studies testing new, improved products. "Scientifically conducted" surveys and polls are used to predict political elections and determine public opinions. Legislation drafted by our elected representatives is often based on, or sometimes completely ignores, the findings of scientific studies. Your tax dollars are used to support many types of basic and applied scientific research.
This is a scientific age, a situation that does not please everyone. Like it or not, science, and its close cousin technology, affect your everyday lives. Your way of life, your health, your standard of living, and that of your children and grandchildren, will be affected by many aspects of science and technology. Our use and misuse of the Earth's natural resources, the tremendous impact of human activities on our environment, and the continued increase of the human population will certainly change the way you live your lives. This textbook is not intended to be issue oriented, but understanding science and how it works is essential for you to understand many specific problems and issues facing our society. We attempt not to make value judgements, but to provide you the intellectual tools to understand and evaluate the science that surrounds you.
The motivation for writing this text grew out of discussions about what to teach first year students in what might be their only college-level biology course. Every biologist had a different opinion about what subjects were so important that they must be covered in a one semester course. To please everyone, the composite subject outline would look like an entire undergraduate curriculum in biology. Many introductory textbooks in biology, containing 1000 to 1500 pages, actually present a very comprehensive compilation of biological facts. Obviously a great deal of the traditional knowledge of biology must be omitted in a small textbook. How did we choose what to leave out?
A number of studies have addressed the problem of decreasing scientific literacy in our country, and a major contributor to the problem is an emphasis on rote memorization of factual information. Science has been taught as factual information without providing students with any knowledge of the process by which the information was acquired or of the conceptual framework that makes sense out of it. The correct question was not what to teach, but how to teach it.
This textbook emphasizes the conceptual framework, the theories, the explanations that make biological science a coherent, organized body of knowledge. No attempt is made to present a comprehensive body of factual information, and as an introductory text, only very important or essential terms are used. By reducing the number of terms and facts to be memorized, we hope to direct your attention to biological concepts. Factual information is presented primarily to illustrate or test predictions. In all cases there are many other examples that could have been used.
Learning concepts is more efficient than just memorizing facts. You can memorize and recite a 100 word poem much more easily than you could memorize a list of 100 unrelated words, simply because the interrelated meanings of the words in a poem make logical connections. We remember interconnected pieces of information much longer and much more easily than a similar number of isolated items. By concentrating on the concepts that interconnect and explain biological facts, we hope to present knowledge that you will retain longer, and that you can apply in the future to new and different situations.
What is science? What makes biology, chemistry, geology, or physics different from history, literature, or art? A dictionary will say that "science is a body of facts or truths systematically arranged and showing the operation of general laws." This definition probably reflects generally held perceptions of science, but nowhere in the dictionary definition is there any suggestion that science is a process. The application of this process in biology, chemistry, geology and physics makes them science. Such a fundamental misunderstanding about science has led to very poor decisions about how to teach science. Courses and textbooks ignoring the process, do not teach science.
Science is composed of two types of facts, which for convenience can be called Type I Facts and Type II Facts. A Type I Fact is an observed phenomenon or datum. These are absolutely true unless the observer made a mistake. Since Type I Facts have the potential to be repeated or made independently by different individuals, Type I Facts can be corrected and confirmed. Observing dancing fairies when you look through a microscope is not a Type I Fact unless other competent observers looking through the same microscope at the same specimen see the same thing. Well-verified Type I Facts come as close to absolute truth or certainty as anything can come.
Type II Facts are the explanatory concepts used to organize and explain Type I Facts. They are accepted as true because they have been extensively tested and not found to be false. If the discovery of Type I Facts is compared to making bricks, then Type II Facts can be compared to constructing a building from the bricks. You need bricks to make a building, but a building is much more useful than a disorganized pile of bricks.
You may not think it sounds very "scientific", but as shall be explained below, Type II Facts cannot be proven to be absolutely true. As a result, Type II Facts are considered conditional truths. Better explanations may be found and further scientific work may result in their modification. However, Type II Facts can be proven absolutely false, and consequently they may be wholly rejected. All Type II Facts that are accepted as true have survived numerous attempts to falsify them. The commonly held view that scientists attempt to prove that theories are true, actually is incorrect. As you shall see, only in falsification is there certainty.
In science a THEORY represents both a body of knowledge, the Type I Facts, and the explanatory concepts constructed to make sense out of them, the Type II Facts. In this text we will examine three major theories, the Cell Theory, the Theory of Heredity, and the Theory of Evolution. Are theories facts? Yes, in every operational way they are. However, theories are conditional facts or truths since we expect new ideas and new findings to be incorporated into the intellectual framework of our explanatory concepts. While major scientific theories are only considered conditional truths, they have been well verified and for this reason biologists and biology students may have a great deal of confidence that major theories will not be falsified completely.
How do scientists define or describe science? The following excerpts are typical of the working view of science as held by its practioners.
"...facts and theories are different things....Facts are the world's data. Theories are structures of ideas that explain and interpret facts. Facts do not go away when scientists debate rival theories to explain them... Moreover, `fact' does not mean `absolute certainty'...In science, `fact' can only mean `confirmed to such a degree that it would be perverse to withhold assent.' ...Philosopher Karl Popper has argued for decades that the primary criterion of science is the falsifiability of its theories. We can never prove absolutely, but we can falsify. A set of ideas that cannot, in principle, be falsified is not science." (Stephen Jay Gould, 1981).
"...scientific theories can never be proven absolutely...Science is not, therefore, truth--at best it is the unending search for truth. The conclusions reached by science are only contingent truths--truths contingent upon man's limited knowledge of himself and the world around him. Now, one may ask what good is a theory if it is not true? A theory is good because it is useful and it is fruitful of new knowledge. Scientific methods have explained more of the empirical world than any alternative approaches, including religion. Science allows man to work in the universe as no other system of knowledge does... Man's ability to act usefully from the predictions of a theory, however, depend upon his ability to test the predictions made by the theory. The process of testing...is more important than the theory itself...Thus, right or wrong, a testable theory always yields new information about the problem it claims to resolve....All good scientific theories work this way. Thus, although scientific truths are always contingent ones, the method by which they are advanced and tested ensures their improvement. In short, the power of scientific theories results from the fact that they are correctable. They may be tested. Whether the theory is right or wrong, these tests yield new information about the world. And, if the theory is wrong, then this new information can be used to invent a new and better theory. Thus, while scientific theories are never perfect, they become better and better with time." (Robert Root-Berstein & Donald McEachron, 1982).
"Science is the human search for a natural explanation of what the universe is: How it is constructed, how it came to be. The only rule of the scientific method is that we must discard any scientific statement if the evidence of our senses shows it is wrong. If there is one rule, one criterion that makes an idea scientific, it is that it must invoke naturalistic explanations for phenomena, and those explanations must be testable solely by the criteria of our five senses." (Niles Eldredge, 1982).
A better definition of science than that usually found in dictionaries is "a human process whose objective is to gain an understanding of the Universe through the use of the hypothetic- deductive method (described below)."
Science ultimately is based upon unproven and unprovable assumptions about the nature of the Universe. (1) The Universe is real, and its nature can be perceived and understood by the human mind. (2) All observable phenomena are the effects of potentially knowable causes. (3) Nature is unified, and the whole Universe operates under one set of rules. When something is discovered about an atom or an apple, something has been discovered about the whole Universe. These assumptions limit the scope of science, and thus science only deals with the known natural Universe. Science makes no assumptions made about the supernatural. Science does not deny the existence of the supernatural, but science has no means of studying anything supernatural. Some people feel that the Universe can be satisfactorily explained without assuming anything supernatural exists. Many people feel that science does not offer a complete view of existence, which they compliment with various religious beliefs.
The cyclical nature of the scientific process, the testing and rejecting of hypotheses, and the replacing of older hypotheses with better explanations allows our scientific knowledge and understanding to accumulate and improve. In other words, science makes progress. The research of scientists becomes incorporated into the hypotheses and theories of the entire scientific community. Thus, science is a human community endeavor that progresses toward an understanding of our Universe.
Real science bears little resemblance to the brilliant, but warped, experiments of mad scientists as in movies or science- fiction novels. Unusual ideas or inspirations of individuals do not attract much support or attention unless supported by solid observational or experimental evidence. The fossil record clearly demonstrates that many species became extinct at the end of the Cretaceous period. Walter Alvarez, a physicist at the University of California at Berkeley, hypothesized that an asteroid impact caused a world-wide climatic catastrophe leading to the mass extinction of dinosaurs and other organisms. Such an hypothesis would attract little scientific support without observational evidence that so far has no other viable explanation. The element iridium, rare in Earth deposits, but rich in meteorites, was found to be 30 times more common in a thin sedimentary deposit at the Cretaceous/Cenozoic geological boundary. Alvarez and his Berkeley associates concluded that the iridium could only have come from an extraterrestrial source, a large meteor that disintegrated upon impact about 65 million years ago. The hypothesized climatic catastrophe is similar to a "nuclear winter", the hypothesized result of multiple nuclear explosions.
If further verified, the Alvarez "meteor impact hypothesis" of the Cretaceous extinction might be called the "meteor impact theory", but usually hypotheses that become accepted as true become incorporated into existing explanations with a larger scope, in this case the theory of evolution. Thus our explanation of the history of life on Earth would be modified, and our understanding of evolution would be improved. Any distinction between minor and major theories is strictly arbitrary, but when we refer to theories, we refer to major explanations. Recently geologists have reported finding evidence of one or more large impact craters of the correct geological age along with other evidence of ancient meteor impacts. Such Type I facts are consistent with the meteor impact hypothesis, enlarge the body of scientific knowledge the hypothesis explains, and increases our confidence that this hypothesis is true, but they do not prove the hypothesis is true.
It is perfectly acceptable in science to hold unpopular or unusual ideas in areas that have not been the subject of intensive observation or testing. Even though these particular ideas are unpopular or not favored to be true, there still exists some chance that everyone else used poor judgement based on their experience and knowledge. However, after hypotheses have been tested until scientists are confident beyond all reasonable doubt that an explanation (a theory) is correct, the scientific community is perfectly justified in refusing to give credence to the work of any dissenting scientist. Astronomers no longer have to consider advocates of a terracentric solar system as colleagues. Geologists are not being unfair when they deny flat- Earth geologists a forum for publishing their ideas. Another example is the literal validity given the Biblical story of creation by many members of the general public and some scientific dissidents. By placing a creation story on a par with the extensively-tested theory of evolution, creationists demonstrate a great lack of understanding about science and its interconnectedness, its intellectual products, and its motives. As readers of this book, you will gain a better understanding of the scientific process and the scientific theories of biology.
No recipe or specific set of rules exists for doing science. Science is just a very systematic application of normal problem- solving thinking, a modified trial and error approach. As scientists, we use our accumulated knowledge, our intuition, and our experience to eliminate many possible, but useless trials.
Fundamentally, science starts with the observation of a particular phenomenon. The next step is constructing a tentative explanation, a HYPOTHESIS, to explain the observations. In many ways this is no more than an educated guess. The type of logic that we employ to intellectually construct hypotheses is INDUCTIVE LOGIC, a pattern of thinking that moves from the specific observations to a general explanation. The use of inductive logic as a formal part of the process of understanding our Universe began during the Renaissance.
If you observe that a green apple tastes sour, you might construct a hypothesis expressing what you guess to be the relationship between greenness and sourness in apples.
Hypothesis: All green apples are sour because they are not yet ripe.
Very often the same observation can generate several hypotheses, and the only rule is that they should offer a possible explanation of the observed phenomenon. Consider the following alternative hypothesis.
Hypothesis: Green apples are sour because that is how the color green tastes.
Both hypotheses offer explanations of the observed phenomenon, but some explanations may seem more plausible than others. Even if you have one hypothesis that you like better than another, how can you decide between them or convince anyone else that one of them might be true? Science simply is not satisified with such tentative explanations, although hypothesizing is a necessary part of science.
In order to test the validity of a general explanation or hypothesis, it is necessary to have a specific case to test. The truth of the hypothesis is assumed and the hypothesis is used to make predictions about other specific cases that should also be true, if the hypothesis is true. The type of thinking that moves from the general explanation to the specific prediction is DEDUCTIVE LOGIC. Deductive logic as a formal part of human thought is much older than inductive logic. The Greek philosophers attempted to deduce the true nature of the Universe. Deduced predictions usually take the form of If..., then... statements. The If clause restates the hypothesis and indicates your assumption of its truth, and the Then clause makes a logical prediction.
Prediction: If the color green tastes sour, then green items other than apples should also taste sour.
Testing such predictions is a very important part of science because it is only through such testing that the relative truth of hypotheses can be determined. Scientists use two general approaches to prediction testing, an EXPERIMENTAL approach or a COMPARATIVE approach. The comparative approach is older and operates generally by comparing the results of additional observations. The experimental approach is much more recent in origin and generally operates by a reductionist method that breaks the problem down into component parts and manipulates one part at a time to determine what contribution each part makes. A comparative approach to testing the "sour-taste-of green" hypothesis might be to accumulate a number of green items and subject them to a taste test, for example, green grass, green paper, and green spinach. Obviously, you would conclude that these items are not sour tasting, therefore, the hypothesis that associates greenness with sourness is false and a better hypothesis must be sought. The comparison of items could be greatly enlarged until it was discovered that greenness usually correlated with sourness in unripe fruit, but sourness was not necessarily a characteristic of the color green. The hypothesis could be adjusted accordingly, and scientific progress would have been made.
An experimental approach might be to consider what characteristics of green apples made them sour, before deciding what else to test or even how to test a more general prediction. After subjecting green apples to considerable examination, you might discover that they were mildly acidic. A number of items could then be tested for their relative acidity to determine if greenness and sourness correlated with acidity. In such a way you would discover that sourness correlated with acidity, but that greenness did not. The comparative approach found out more about fruit, but the reductionist nature of the experimental approach focused our study of sourness on acidity. The scientist's approach should be appropriate for the question she or he is interested in answering.
Both the experimental and comparative methods are equally valid, but each method has its limitations and its strengths. A verifiable hypothesis explaining genetic inheritance was not discovered using the comparative approach. Gregor Mendel applied experimental methods to discover the nature of inheritance in garden peas. The comparative approach was used extremely successfully by Charles Darwin to conclude that evolution proceeded by descent with modification.. In the physical sciences, the experimental approach has been extremely successful, and has been used so exclusively that some physical scientists doubt the validity of the comparative method. However, in biology there are levels of organization too complex for the reductionist experimental approach to be used successfully. Describing every single chemical reaction and molecule within an organism will not answer questions about how that organism interacts with other organisms or the environment.
Research involves a very diligent study of a particular phenomenon or question by applying the scientific method. There are two general justifications for conducting or pursuing a particular research project. Basic research investigates some subject because it is inherently interesting, simply the pursuit of knowledge for the sake of knowledge alone. Applied research pursues studies that offer promise of solving some problem of interest to humans or improving the human condition. Studying the reproductive biology of a primitive flowering tree in rain forests would be basic research. Producing a vaccine against the AIDS virus would be applied research.
In reality, the distinction between applied and basic research is not made so easily. Pursuit of both types of research are necessary and worthwhile. Basic research, undertaken for intellectual reasons alone, can and has led frequently to results of value to human problems. Historically it can be demonstrated that many solutions of applied research problems have depended on the results of basic research conducted a decade or more before. Using temperate zone tax dollars to study rain forest tree reproduction may seem very esoteric, but the destruction of rain forests and their importance in helping maintain world climatic patterns make such studies very applied. Unfortunately, no one can accurately guess what will be important or significant in the future, so if a research project has scientific merit, it deserves to be studied, even if no present usefulness can be perceived. In the real world, scientists also must demonstrate that the research can be accomplished technically and that the cost is not excessive in comparison to the potential gain in knowledge and benefits. Cost versus potential benefit is difficult to assess for big, expensive research projects like the Supercollider and the Human Genome Project.
The process of science and scientific research may appear very complicated to many people. Many students may be discouraged from pursuing a career in science because the imposing image of science convinces them they cannot contribute to such a process. This misconception may have discouraged many interested people from pursuing a scientific education and may account for some of the distrust and misunderstandings the general public has about science. Whatever the origins of the problem, science is not a mysterious process. The scientific method is based on normal human thought processes that you use unconsciously every time you solve a problem. Consider the following not-too-unusual sequence of events that illustrates the problem-solving scientific process.
You come home at night, open the door, turn on the switch to light the lamp, and the light does not come on. If the light had come on, you never would have given a second thought, but now you have a problem to solve, or you remain in the dark. Hypothesis Formation You compare this observation with your "theory of electricity" compiled from a high school science course, and your knowledge of the workings of lights, and other past events. What could explain your observation that is consistent with your knowledge of electricity? Perhaps, you logically induce, THE ELECTRICITY IS OUT IN THE ENTIRE NEIGHBORHOOD (hypothesis).
What can be deduced logically from such a hypothesis? If the electricity is out in the entire neighborhood, then every house in the neighborhood should be dark. This certainly is a testable prediction. By walking back outside and examining the surrounding houses, you can determine if that prediction is true or not. If some of the houses show light, then the prediction is false, and since the prediction was logically derived from the hypothesis, the hypothesis must be false as well. The falsification is absolute, and the hypothesis must be discarded.
This is a good opportunity to explain and demonstrate why hypotheses cannot ever be proven absolutely true. Suppose that in testing your hypothesis you had observed that every house was completely dark. The prediction was true; however, that alone did not prove the hypothesis was true because false hypotheses also can yield true predictions. If you don't understand this, you might still be sitting in the dark waiting for the electricity to come back on when all of your neighbors return home from the movies. (Just by chance they all decided to go out on the same night.) You observed the dark houses correctly, the observation supported your explanation, but you wrongly assumed the cause.
Maybe the lights don't come on because THE SWITCH IS BROKEN (another hypothesis). That certainly explains the observations.
This is a toughy! You can't think of any good predictions. If the switch is broken, then maybe jiggling it will cause it to work. That's a really weak prediction, and you try jiggling the switch, but nothing happens. At this point you decide to reject this hypothesis in favor of a better one. Why? Even though it's possible, based on your experiences it's improbable; broken switches are rather unusual. Besides you don't have any really good way to test the hypothesis at this point.
Scientists also use such evaluations. Based on their experiences, guesses, and even intuitions, some possible hypotheses are rejected because they seem improbable, or because there is no way to test the predictions. Judgements like this in science may be very pragmatic and they can save a lot of time and money, or they can be all too humanly wrong.
Maybe the lamp did not light because THE LIGHT BULB IS BURNED OUT (hypothesis).
You like this hypothesis as soon as you think of it. In your experience bulbs have burned out frequently. Although other hypotheses remain possible (short circuit, fuse or circuit breaker blown, plug pulled, etc.) you decide to test the idea that you think is most likely to be profitable.
If the bulb is burned out, then replacing the burned out bulb with a new one will allow the lamp to light. Great! Now you grope to a closet, find a new bulb, and return to the lamp. After replacing the bulb you try the switch, and the lamp lights. Congratulations! Thanks to real scientific thinking, the problem has been solved! The primary difference between day-to-day problem solving and science is that in science the hypotheses, the logical predictions, and the method of testing must be explicitly stated, whereas in daily life you actually solve problems without consciously articulating the process. Yet the same inductive- deductive cycling of logic is used. To become more proficient problem-solvers you must become consciously aware of the actual nature of the process, and like any other skill you need education, experience, and practice to develop your innate talents. To become a proficient scientist requires a lot of education, training, and practice. Scientists are not necessarily more intelligent than science students, but scientists are professional problem-solving thinkers, and as students you may have to work very hard to keep up with your scientist/teachers.
As a result of solving the light problem, your confidence in your "theory of electricity" has improved. Whenever a scientist tests a prediction and it is not falsified, they become more confident the theory is true even though they have not proven it true, just as you did not prove that the light had burned out.
Say what!? Read over the preceeding sequence of events again if you have to, but nowhere is there proof that the bulb was burned out. Yes, the prediction about the new bulb was true, but remember a false hypothesis can yield a true prediction so you are never really certain.
If the bulb was burned out, then it should make a tinkling sound when you shake it and it won't work in another lamp. The "burned-out" bulb doesn't tinkle, so rather than simply discarding the original bulb, you decide to test this hypothesis by trying the "burned-out" bulb in another lamp. To your surprise, it lights! The prediction was falsified, and therefore, your hypothesis was false, even though you solved the immediate problem of lighting the house.
What new hypothesis can account for all of the observations so far? Maybe the bulb was loose in the socket and only needed to be tightened rather than replaced. This hypothesis is consistent with all of the facts, but can you prove it true? You could experiment with loosening the bulb in the lamp to test the prediction that sufficiently loose bulbs will fail to light. But there is no way to repeat such an historical event and prove that it actually happened the way you think it happened. Many events in biology are also historical events. Even if they cannot be tested directly scientists can develop confidence in hypotheses that are consistent with enough facts, particularly if no other hypothesis can be thought of that does so. There is a high probability that the bulb was loose in the socket, but no certainty. Many historical events in biology, like evolution, can yield testable predictions based on the assumption that evolutionary change was true. If enough of these predictions are tested and cannot be falsified, we gain confidence in the truth of the original assumptions.
Even if well verified, the "loose-bulb" hypothesis does not really gain the status of a theory. Remember, in one form or another, you already have a Theory of Electricity, the sum total of your knowledge and explanations of a variety of phenomena incorporating numerous hypotheses. When sufficiently verified, the "loose-bulb" hypothesis simply takes its place within your Theory of Electricity. Thus hypotheses and theories do not simply represent a difference in confidence. Useful hypotheses usually deal with more specific issues than theories. To solve the "light-out" problem above, you did not start by asking, "What is the nature of electricity?" There was no useful way to examine your entire theory.
As long as this example is still fresh, we should also point out that hypotheses like "The lamp does not feel like coming on" or "The lamp genie must not have been paying attention when I turned the switch on" offer no useful approaches to studying a phenomenon of the natural world. Science has no way to test whether lamps have feelings or urges, or whether a lamp genie exists, so science can make no useful statements about the supernatural.
An important source of confidence in the truth of theories comes from the mutual support that various scientific theories give to each other. The Theory of Heredity and the Theory of Evolution were both mutually strengthened when it was determined that they were not mutually exclusive. Both are now intertwined with Cell Theory and incorporated into our overall understanding of biology. The same thing can be said for Heredity, Evolution, and Ecology. Each new field, each level of organization, has produced conceptual explanations of its phenomena that could have potentially falsified other theories. When all of the major theories of biology dovetail together and intertwine in a very complimentary manner, our confidence in the overall truth of these explanatory concepts increases greatly.
Hypotheses and theories running counter to other explanations within biology and the physical sciences generally lower our confidence in their truth, and scientists actively will seek alternative explanations of the observations and evidence that are consistent with other hypotheses. Astronomy, physics, chemistry, and geology, the major fields of the physical sciences, have produced their own theories to explain their own observations and evidences, but many aspects of these fields are significant to biology. In Chapter 11 you will learn that a conceptual change in geology preceeded and greatly influenced evolutionary concepts in biology.
Origin of life theories account for evidence and data from geology, astronomy, and chemistry (Chapt. 2). To explain observed phenomena, astronomers have developed hypotheses concerning the origin of stars, galaxies, and the Universe, and incorporated these explanations into a cosmological theory, which agrees very well with current biological theories on the origin of life. Astronomical observations of interstellar molecules support explanations of the spontaneous generation of organic molecules, the building blocks of life. A mutually supportive interaction between chemistry and biology is fairly obvious, although we purposely do not provided very many details in this text. Biology is not an isolated science, and its interconnections with the physical sciences demonstrate that science strives to become an integrated explanation of the natural Universe. This body of knowledge offers a considerable educational challenge to any student or scholar who wishes to gain an overall scientific understanding of the Universe and ourselves.
Biology is often referred to as the life sciences, that area of science that studies the phenomenon of life. Most of you are probably fairly confident that you can distinguish living organisms from non-living objects. Living organisms can interact with their environment, grow, and reproduce. Biology involves the study of all aspects of living organisms from their chemical constituents to the workings of the biosphere, that portion of the Earth where living organisms are found. Biology can be organized in two general ways, either by the organism being studied or by the level of biological organization being studied. Thus, biology can be subdivided into Botany, Zoology, and Microbiology, and each of these categories can be further subdivided by major groups of organisms being studied. This type of subdivision only tells you what organism is being studied.
There are various organizational levels of biological study, and at the extremes there are interfaces with the physical sciences of chemistry, geology, and physics. Broadly speaking, biology can be thought of as starting at a molecular level of organization, biochemistry, where biology interfaces with chemistry. Above this the biochemical constituents of life are organized into structures at a cellular level. The development and differentiation of cells, the composition of tissues and organs, their functional roles, and adaptive significance all combine at an organismal level. Further levels of complexity exist at the level of populations, communities, and ecosystems. Various subdivisions of these organizational categories exist as well.
To some extent these categories form a hierarchy of organization, with each level being a component part of the next level, so knowledge of lower levels of organization are necessary to understand some aspects of more complex levels. This text is organized to reflect this biological hierarchy. Unit I, Cell Biology, considers the components and functions of cells, the reproduction of cells, and the development of organisms. Unit II, Genetics, examines the nature of inheritance from the perspective of individual organisms to populations. Unit III, Evolution, considers the mechanisms of long term changes in the genetics of populations. Finally, Unit IV, Ecology, examines the organizational levels from the adaptations of organisms, to populations, to communities of organisms, to ecosystems. This last level of organization includes the interactions of biological communities with their physical environment. Organismally, we have attempted to be diverse by including examples from many groups of organisms. Whenever it seemed appropriate, we have sought examples directly from the original literature where a phenomenon was described.
Science is a process that produces an improving explanation of the natural Universe. The process employed in science is similar to problem-solving thinking that cycles between the inductive and deductive phases of generating probable explanations, hypotheses, and then testing the predictions logically derived from them. Science employs both comparative and experimental methods to test hypotheses, and scientists seek answers to both basic and applied questions. Based on the results of testing, hypotheses are conditionally accepted as true, rejected as false, or modified accordingly. Well-verified hypotheses become incorporated into larger, explanatory concepts, theories. The truths of science are conditional truths because it is likely that they will change as we gain more knowledge, but in every operational way scientific theories are treated as facts. Each major field of science has its own theories, but many interconnections exist between fields of science and such successful interrelationships among theories increases our confidence in their truth.
Biology is an area of science that studies the phenomenon of life. Rather than presenting a comprehensive array of terms and scientific "facts", this text attempts to illustrate the major concepts, the explanations, and the theories of biology. We will show how these concepts were developed, how they were tested, and why biologists have confidence in their truth. This teaching approach was adopted in an effort to provide a better understanding of what the important products of science are and how they were obtained. At all times, the terms hypothesis and theory will be used as described above.
Genesis and Development of a Scientific Fact. L. Fleck, 1979, Univ. of Chicago Press, Chicago.
Introductory Readings in the Philosophy of Science. E. D. Klemke, R. Hollinger, and A. D. Kline (eds.), 1980, Prometheus Books, New York.
Science as a Way of Knowing, The Foundations of Modern Biology. J. A. Moore, 1993, Harvard University Press, Cambridge, MA.
The Ascent of Man. J. Bronowski, 1973, Little, Brown, & Co., Boston.
The Limits of Science. P. B. Medawar, 1984, Harper and Row, New York.
The Scientific Attitude. F. Grinnell, 1987, Westview Press, Boulder.
The Scientific Method in Biology. J. E. Luken, 1988, Journal of College Science Teaching, February 274-280.
The Treatment of Theory in Textbooks. L. S. Lerner and W. J. Bennetta, 1988, The Science Teacher, April, 37-41. Chapt. 1 - Page 2