CONCEPTS IN BIOLOGY
PART I. INTRODUCTION
1. What Is Biology?
1.2. Science and the Scientific Method
Most textbooks define biology as the science that deals with life. This definition seems clear until you begin to think about what the words science and life mean.
Science is actually a process used to solve problems or develop an understanding of repetitive natural events that involves the accumulation of knowledge and the testing of possible answers. The process has become known as the scientific method. The scientific method is a way of gaining information (facts) about the world by forming possible answers to questions, followed by rigorous testing to determine if the proposed explanations are supported by the facts.
Basic Assumptions in Science
When using the scientific method, scientists make some basic assumptions:
• There are specific causes for naturally reoccurring events observed in the natural world.
• The causes for events in nature can be identified.
• There are general rules or principles that can be used to describe what happens in nature.
• An event that occurs repeatedly probably has the same cause each time it occurs.
• What one person observes can be observed by others.
• The same fundamental rules of nature apply, regardless of where and when they occur.
For example, we have all observed lightning with thunderstorms. According to the assumptions that have just been stated, we should expect that there is a cause of all cases of lightning, regardless of where or when they occur, and that all people could make the same observations. We know from scientific observations and experiments that
(1) lightning is caused by a difference in electrical charge,
(2) the behavior of lightning follows the same general rules as those for static electricity, and
(3) all lightning that has been measured has had the same cause wherever and whenever it has occurred regardless of who made the observation.
Scientists distinguish between situations that are merely correlated (happen together) and those that are correlated and show cause-and-effect relationships. Many events are correlated, but not all correlations show cause-and-effect. When an event occurs as a direct result of a previous event, a cause-and-effect relationship exists. For example, lightning and thunder are correlated and have a cause-and-effect relationship. Lightning causes thunder.
The relationship between ingesting microorganisms and foodborne illness can be difficult to figure out. Because people have experienced bacterial, viral, or fungal infections, many assume that all microbes cause disease. In addition, the media portray all microbes as dangerous. Companies tell us that you should buy their antimicrobial product. They claim that their product will kill all the microbes, and therefore you will not come down with a foodborne illness. However, scores of different scientists have demonstrated through countless laboratory experiments that only a small number of microbes are pathogenic; that is, capable of causing harm. In fact, it turns out that most microbes are beneficial. These experiments have led to the identification of specific mechanisms by which pathogens cause harm. For example, a specific toxin (poison) can be collected from a suspect bacterium, purified, and administered to a laboratory animal in its food. If the animal displays the predicted foodborne illness symptoms, the experiment lends credibility to the fact that the microbe is responsible for that illness. Knowing that a cause- and-effect relationship exists enables us to make a prediction. If the same set of circumstances occurs in the future, the same effect will result.
The Scientific Method
The term scientifically is used in commercials, “science” programs on TV, public meetings, and in many other situations. Is this term being used correctly? In most cases the answer is “no!” In most of these situations, the term scientifically is used to mean “precisely,” or with great accuracy. Science is a method that requires setting up a control group to which the experimental group is compared.
The scientific method involves an orderly, careful search for information. The method involves a continual checking and rechecking to see if previous conclusions are still supported by new evidence. If new evidence is not supportive, scientists discard or change their original ideas. Thus, scientific ideas undergo constant reevaluation, criticism, and modification as new discoveries are made. This can be very bewildering to the general public and can lead to people making comments such as, “Can’t they make up their minds?” or “That’s not what they said the last time.” The scientific method has several important components:
• Careful observation
• The construction and testing of hypotheses
• An openness to new information and ideas
• A willingness to submit one’s ideas to the scrutiny of others
The purpose of this method is to help scientists avoid making faulty assumptions and false claims. It is closely tied to the assumptions listed earlier and consists of several widely accepted steps (figure 1.2). However, scientists do not typically follow these steps from the first step (observation) to the last (communication). They take advantage of the work done by others and jump in and out of this series at various places.
FIGURE 1.2. The Scientific Method
The scientific method is a way of thinking that involves making hypotheses about observations and testing the validity of the hypotheses. When hypotheses are disproved, they are revised and tested in their new form. Throughout the scientific process, people communicate their ideas. Scientific theories and laws develop as a result of people recognizing broad areas of agreement about how the world works. These laws and theories help people develop their approaches to scientific questions.
Scientific inquiry begins with an observation. We make an observation when we use our senses (i.e., smell, sight, hearing, taste, touch) or an extension of our senses (e.g., microscope, sound recorder, X-ray machine, thermometer) to record an event.
However, there is a difference between a scientific observation and simple awareness. For example, you might hear a sound or see something without really observing it. You have probably seen a magician, an illusionist, or a mystic perform tricks, but do you really know what’s going on ‘behind the scenes’? (figure 1.3) When scientists talk about their observations, they are referring to careful, thoughtful recognition of an event—not just casual notice. Scientists train themselves to improve their observational skills, because careful observation is important in all parts of the scientific method.
FIGURE 1.3. Observation
Careful observation is an important part of the scientific method. (a) This technician is making observations on the characteristics of soil and recording the results. (b) What is really going on here? What are you not observing?
Questioning and Exploration
As scientists make observations, they begin to develop questions. How does this happen? What causes it to occur? When will it take place again? Can I control the event to my benefit? Forming questions is not as simple as it might seem, because the way you ask questions determines how you answer them. A question that is too broad or too complex may be impossible to answer; therefore, a great deal of effort is put into asking the question in the right way. In some situations, this is the most time-consuming part of the scientific method; asking the right question is critical to how you look for answers.
Let’s say that you have observed a cat catch, kill, and eat a mouse. You could ask several kinds of questions:
1a. What motivates a cat to hunt?
1b. Do cats hunt more when they are hungry?
2a. Why did the cat kill the mouse?
2b. Is the killing behavior of the cat instinctive or learned?
3a. Did the cat like the taste of the mouse?
3b. If given a choice between mice and canned cat food, which would cats choose?
Although questions 1a, 2a, and 3a are good questions, it would be very difficult to design an experiment to evaluate them. On the other hand questions 1b, 2b, and 3 b lend themselves to experiment. The behavior of hungry and recently fed cats could be compared. The behavior of mature cats that have not had an opportunity to interact with live mice could be compared to that of mature cats who had accompanied their mothers as they hunted and killed mice. Cats could be offered a choice between a mouse and canned cat food and their choices could be recorded (figure 1.4).
FIGURE 1.4. Questioning
The scientific method involves forming questions about what you observe.
Once a decision has been made about what question to ask, scientists explore other sources of knowledge to gain more information. Perhaps the question has already been answered by someone else. Perhaps several possible answers have already been rejected. Knowing what others have already done can save time and energy. This process usually involves reading appropriate science publications, exploring information on the Internet, and contacting fellow scientists interested in the same field of study. After exploring these sources of information, a decision is made about whether to continue to consider the question. If the scientist is still intrigued by the question, he or she constructs a formal hypothesis and continues the process of inquiry at a different level.
A hypothesis is a statement that provides a possible answer to a question or an explanation for an observation that can be tested. A good hypothesis must have the following characteristics:
(1) It must be logical.
(2) It must account for all the relevant information currently available.
(3) It must allow one to predict future events relating to the question being asked.
(4) It must be testable.
(5) Furthermore, if one has a choice of several hypotheses, one should use the simplest one with the fewest assumptions.
Just as deciding which questions to ask is often difficult, forming a hypothesis requires much critical thought and mental exploration.
Scientists test a hypothesis to see if it is supported or disproved. If they disprove the hypothesis, they reject it and must construct a new hypothesis. However, if they cannot disprove a hypothesis, they are more confident in the validity (able to be justified; on target) of the hypothesis, even though they have not proven it true in all cases and for all time. Science always allows for the questioning of ideas and the substitution of new explanations as new information is obtained. As new information is obtained, an alternative hypothesis may become apparent and may explain the situation better than the original hypothesis. It is also possible, however, that the scientists have not made the appropriate observations to indicate that the hypothesis is wrong.
The test of a hypothesis can take several forms.
(1) Collecting relevant information
In some cases collecting relevant information that already exists may be an adequate test of a hypothesis. For example, suppose you visited a cemetery and observed, from reading the tombstones, that an unusually large number of people of various ages died in the same year. You could hypothesize that an epidemic of disease or a natural disaster caused the deaths. To test this hypothesis, you could consult historical newspaper accounts for that year.
(2) Making additional observations
Often making additional observations may be all that is necessary to test a hypothesis. For example, suppose you hypothesized that a certain species of bird uses holes in trees as places to build nests. You could observe several birds of the species and record the kinds of nests they build and where they build them.
(3) Devising an experiment
A common method for testing a hypothesis involves devising an experiment. An experiment is a re-creation of an event or occurrence in a way that enables a scientist to support or disprove a hypothesis. In every experiment, the scientist tries to identify if there is a relationship between two events.
This can be difficult, because a particular event may involve many separate factors, called variables. For example when a bird sings many activities of its nervous and muscular systems are involved. It is also stimulated by a wide variety of environmental f actors. Understanding the variables involved in bird song production might seem an impossible task. To help unclutter such a situation, scientists break it up into a series of simple questions and use a controlled experiment to answer each question.
A controlled experiment allows scientists to construct a situation so that only one variable is present. A typical controlled experiment includes two groups: one group in which the variable is manipulated in a particular way and one group in which there is no manipulation. The group in which there is no manipulation of the variable is called the control group; the other group is called the experimental group.
The situation involving bird song production would have to be broken down into a large number of simple questions, such as the following:
Do both males and females sing?
Do they sing during all parts of the year?
Is the song the same in all cases?
Do some birds sing more than others?
What parts of their body are used to produce the song? What situations cause birds to start or stop singing?
Each question would provide the basis for the construction of a hypothesis, which could be tested by an experiment. Each experiment would provide information about a small part of the total process of bird song production. For example, in order to test the hypothesis that male sex hormones produced by the testes are involved in stimulating male birds to sing, an experiment could be performed in which one group of male birds had their testes removed (the experimental group) but the control group was allowed to develop normally.
The presence or absence of testes would be manipulated by the scientist in the experiment and would be the independent variable. The singing behavior of the males would be the dependent variable, because, if sex hormones are important, the singing behavior observed will change, depending on whether the males have testes or not (the independent variable). In an experiment, there should be only one independent variable, and the dependent variable is expected to change as a direct result of the manipulation of the independent variable. After the experiment, the new data (facts) gathered would be analyzed. If there were no differences in singing between the two groups, scientists could conclude that the independent variable (presence or absence of testes) evidently did not have a cause-and-effect relationship with the dependent variable (singing). However, if there were a difference, it would be likely that the independent variable caused the difference between the control and experimental groups. In the case of songbirds, removal of the testes does change their singing behavior.
Scientists draw their most reliable (trustworthy) conclusions from multiple experiments. This is because random events having nothing to do with the experiment may have altered one set of results and suggest a cause-and-effect relationship when none actually exists. For example, if the experimental group of birds became ill with bird flu, they would not sing. Scientists use several strategies to avoid the effects of random events in their experiments; including using large numbers of animals in experiments and having other scientists repeat their experiments at other locations. With these strategies, it is less likely that random events will lead to false conclusions.
Scientists must try to make sure that an additional variable is not accidentally introduced into experiments. For example, the operation necessary to remove the testes of male birds might cause illness or discomfort in some birds, resulting in less singing. A way to overcome this difficulty would be to subject all the birds to the same surgery but to remove the testes of only half of them. (The control birds would still have their testes.) The results of an experiment are only scientifically convincing when there is just one variable, when the experiment has been repeated many times, and when the results for all experiments are the same.
During experimentation, scientists learn new information and formulate new questions, which can lead to even more experiments. One good experiment can result in many new questions and experiments. For example, the discovery of the structure of the DNA molecule by James D. Watson and Francis W. Crick (1953), resulted in thousands of experiments and stimulated the development of the entire field of molecular biology (figure 1.5).
As the processes of questioning and experimentation continue, it often happens that new evidence continually and consistently supports the original hypothesis and other closely related hypotheses. When the scientific community sees how these hypotheses and facts fit together into a broad pattern, they come together to write a scientific theory or law.
The Development of Theories and Laws
As observations are made and hypotheses are tested, a pattern may emerge that leads to a general conclusion. This process of developing general principles from the examination of many sets of specific facts is called inductive reasoning, or induction. For example, when people examine hundreds of species of birds, they observe that all kinds lay eggs. From these observations, they may develop the principle that laying eggs is a fundamental characteristic of birds, without examining every species of bird.
FIGURE 1.5. One Discovery Leads to Others
The discovery of the structure of the DNA molecule was followed by much research into how the molecule codes information, how it makes copies of itself, and how the information is put into action.
Once such a principle is established, it can be used to predict additional observations in nature. The process of using general principles to predict the specific facts of a situation is called deductive reasoning, or deduction. For example, after the general principle that birds lay eggs is established, one might deduce that a newly discovered species of bird also lays eggs. In the process of science, both induction and deduction are important thinking processes used to increase our understanding of the nature of our world and to formulate scientific theories and laws.
You have probably heard people say “I have a theory” about such-and-such an event. However, scientists would say you have a guess or a suspicion about what is going on, not a theory. When scientists use the term theory, they mean something very different. A scientific theory is a widely accepted, plausible, general statement about fundamental concepts in science that explain why things happen. An example of a biological theory is the germ theory of disease. This theory states that certain diseases, called infectious diseases, are caused by living microorganisms that are capable of being transmitted from one person to another. When these microorganisms reproduce within a person and the populations of microorganisms increase, they cause disease. As you can see, this is a very broad statement, which is the result of years of observation, questioning, experimentation, and data analysis. The germ theory of disease provides a broad overview of the nature of infectious diseases and methods for their control. However, we also recognize that each kind of microorganism has particular characteristics, which determine the kind of disease condition it causes and the appropriate methods of treatment. Furthermore, we recognize that there are many diseases that are not caused by microorganisms, such as genetic diseases.
Theories are different from hypotheses. A hypothesis provides a possible explanation for a specific question; a theory is a broad concept that shapes how scientists look at the world and how they frame their hypotheses. For example, when a new disease is encountered, one of the first questions asked is “What causes this disease?” A hypothesis might be constructed, which states, “The disease is caused by a microorganism.” This is a logical hypothesis, because it is consistent with the general theory that many kinds of diseases are caused by microorganisms (the germ theory of disease).
Because theories are broad, unifying statements, there are few of them. However, just because theories exist does not mean that testing stops. As scientists continue to gain new information, they may find exceptions to a theory or, rarely, disprove a theory.
A scientific law is a uniform or constant fact of nature that describes what happens in nature. An example of a biological law is the biogenetic law, which states that all living things come from preexisting living things. Although laws describe what happens and theories describe why things happen, there is one way in which laws and theories are similar. Both laws and theories have been examined repeatedly and are regarded as excellent predictors of how nature behaves.
One central characteristic of the scientific method is the importance of communication among colleagues. For the most part, science is conducted out in the open, under the critical eyes of others who are interested in the same kinds of questions. An important part of the communication process involves the publication of articles in scientific journals about one’s research, thoughts, and opinions. This communication can occur at any point during the process of scientific discovery.
Scientists may ask questions about unusual observations. They may publish preliminary results of incomplete experiments. They may publish reports that summarize large bodies of material. And they may publish strongly held opinions that are not supportable with current data. This provides other scientists with an opportunity to criticize, make suggestions, or agree (figure 1.6). Scientists attend conferences, where they can engage in dialog with colleagues. They also interact in informal ways by phone and the Internet. The result is that most of science is subjected to examination by many minds as it is discovered, discussed, and refined.
FIGURE 1.6. Communication
One important way that scientists communicate is through publications in scientific journals.
Table 1.1 summarizes the processes involved in the scientific method and gives an example of how scientific investigation proceeds from an initial question to the development of theories and laws.
TABLE 1.1. The Nature of the Scientific Method
Component of Science Process
Description of Process
Example of the Process in Action
Recognize that something has happened and that it occurs repeatedly. (Empirical evidence is gained from experience or observation.)
Doctors observe that many of their patients who are suffering from tuberculosis fail to be cured by the use of the medicines (antibiotics) traditionally used to treat the disease.
Ask questions about the observation, evaluate the questions, and keep the ones that will be answerable.
Have the drug companies modified the antibiotics? Are the patients failing to take the antibiotics as prescribed?
Has the bacterium that causes tuberculosis changed?
Explore other sources of information.
Go to the library.
Talk to others who are interested in the same problem.
Communicate with other researchers to help determine if your question is a good one or if others have already answered it.
Read medical journals.
Contact the Centers for Disease Control and Prevention.
Consult experts in tuberculosis.
Attend medical conventions.
Contact drug companies and ask if their antibiotic formulation has been changed.
Form a hypothesis.
Pose a possible answer to your question.
Be sure that it is testable and that it accounts for all the known information.
Recognize that your hypothesis may be wrong.
Hypothesis: Tuberculosis patients who fail to be cured by standard antibiotics have tuberculosis caused by antibiotic-resistant populations of the bacterium Mycobacterium tuberculosis.
Test the hypothesis (experimentation).
Set up an experiment that will allow you to test your hypothesis using a control group and an experimental group.
Be sure to collect and analyze the data carefully.
Set up an experiment in which samples of tuberculosis bacteria are collected from two groups of patients: those who are responding to antibiotic therapy and those who are not responding to antibiotic therapy.
Grow the bacteria in the lab and subject them to the antibiotics normally used to see if the bacteria from these two groups of patients respond differently.
Experiments consistently show that the patients who are not recovering have strains of bacteria that are resistant to the antibiotic being used.
Find agreement with existing scientific laws and theories or construct new laws or theories.
If your findings are seen to fit with current information, the scientific community will recognize them as being consistent with current scientific laws and theories.
In rare instances, a new theory or law may develop as a result of research.
Your results are consistent with the following laws and theories:
• Mendel’s laws of heredity state that characteristics are passed from parent to offspring.
• The theory of natural selection predicts that, when populations of Mycobacterium tuberculosis are subjected to antibiotics, the bacteria that survive will pass on their ability to survive exposure to antibiotics to the next generation and that the next generation will have a higher incidence of these characteristics.
Form a conclusion and communicate it.
You arrive at a conclusion.
Throughout the process, communicate with other scientists by both informal conversation and formal publications.
You conclude that the antibiotics are ineffective because the bacteria are resistant to the antibiotics. You write a scientific article describing the experiment and your conclusions.
1.2. CONCEPT REVIEW
3. What is the difference between simple correlation and a cause-and-effect relationship?
4. How does a hypothesis differ from a scientific theory or a scientific law?
5. List three objects or processes you use daily that are the result of scientific investigation.
6. The scientific method cannot be used to deny or prove the existence of God. Why?
7. What are controlled experiments? Why are they necessary to support a hypothesis?
8. List the parts of the scientific method.