1.4 What Is Science?  Science is the systematic inquiry – through observation and experiment – into the origins, structure, and behavior of living and nonliving environments

1.4 What Is Science?  Science is based on the principle that all events have natural causes  The belief that some events happen through supernatural forces (e.g., the actions of Greek gods)  The belief that all events can be traced to natural causes that we can comprehend (natural causality)  Corollary: Evidence gathered from nature has not been deliberately distorted to fool us

1.4 What Is Science?  The scientific method is an important tool of scientific inquiry  The scientific method consists of six interrelated elements  Observation  Question  Hypothesis  Prediction  Experiment  Conclusion

1.4 What Is Science?  The scientific method is an important tool of scientific inquiry (continued)  Scientific inquiry is a rigorous method for making observations  The scientific method for inquiry follows six steps

1.4 What Is Science?  The six steps of scientific inquiry 1. Observation of a specific phenomenon 2. The observation, in turn, leads to a question 3. The question leads to formulation of a hypothesis, based on previous observations, which is offered as an answer to the question

1.4 What Is Science?  The six steps of scientific inquiry (continued) 4. The hypothesis leads to a prediction, which is the expected outcome of testing if the hypothesis is correct 5. The prediction is tested by carefully designed additional observations or carefully controlled manipulations called experiments 6. The experiments produce results that either support or refute the hypothesis, allowing the development of a conclusion

1.4 What Is Science?  Biologists test hypotheses using controlled experiments  Two types of situations are established  A baseline or control situation in which all possible variables are held at a constant  An experimental situation in which one factor, variable, is manipulated to test the hypothesis to determine that this variable is the cause of an observation  Science is useless unless communicated  The scientific method is illustrated by experiments by Francesco Redi and Malte Andersson

Figure E1-1 The experiment of Francesco Redi illustrates the scientific method Observation: Question: Hypothesis: Prediction: Experiment: Conclusion: Experimental variable: Controlled variables: Experimental situation Control situation Results Leave the jar uncovered Leave exposed for several days Flies swarm around and maggots appear Cover the jar with gauze Leave covered for several days Flies are kept from the meat; no maggots appear gauze prevents the entry of flies time, temperature, place Obtain identical pieces of meat and two identical jars Place meat in each jar IF the hypothesis is correct, THEN keeping the flies away from the meat will prevent the appearance of maggots. The experiment supports the hypothesis that flies are the source of maggots and that spontaneous generation of maggots does not occur. Flies swarm around meat left in the open; maggots appear on the meat. Where do maggots on the meat come from? Flies produce the maggots.

Figure E1-2 The experiment of Malte Andersson Observation: Question: Hypothesis: Prediction: Experiment: Conclusion: Experimental variable: Controlled variables: Experimental groups Control groups Results Do not change the tail Release the males, wait a week, count the nests Average of about one nest per male Male widowbirds have extremely long tails. Why do males, but not females, have such long tails? Males have long tails because females prefer to mate with long-tailed males. IF females prefer long-tailed males, THEN males with artificially lengthened tails will attract more mates. Divide male birds into four groups Manipulate the tails of the males length of tail location, season, time, weather Cut the tail and re-glue in place Release the males, wait a week, count the nests Average of about one nest per male Cut the tail to half of the original length Release the males, wait a week, count the nests Average of less than half a nest per male Add feathers to double the tail length Release the males, wait a week, count the nests Average of About two nests per male The hypothesis that female widowbirds prefer to mate with long-tailed males (and are less likely to mate with short-tailed males) is supported.

1.4 What Is Science?  Scientific theories have been thoroughly tested  A scientific theory is a general and reliable explanation of important natural phenomena that has been developed through extensive and reproducible observations and experiments  A scientific theory is best described as a natural law, a basic principle derived from the study of nature, which has never been disproven by scientific inquiry

1.4 What Is Science?  Scientific theories have been thoroughly tested (continued)  The cell theory (that all living organisms are composed of cells) and the theory of evolution are fundamental to the study of biology  Natural causality is the principle that all events can be traced to natural causes  Natural laws apply to every time and place  Scientific inquiry is based on the assumption that people perceive natural events in similar ways

1.4 What Is Science?  Scientific theories have been thoroughly tested (continued)  New scientific evidence may prompt radical revision of existing theory  For example, the discovery of prions

1.4 What Is Science?  Scientific theories have been thoroughly tested (continued)  Before 1980, all known infectious diseases contained DNA or RNA  In 1982, Stanley Prusiner showed that the infectious sheep disease scrapie is caused by a protein (a “protein infectious particle,” or prion)  Prions have since been shown to cause “mad cow disease” and diseases in humans  The willingness of scientists to revise accepted belief in light of new data was critical to understanding and expanding the study of prions

1.4 What Is Science?  Scientific theories involve both inductive and deductive reasoning  Inductive reasoning is used in the development of scientific theories  A generalization is created from many observations that support it and none that contradict it  For example, the theory that Earth exerts gravitational forces on objects began from repeated observations of objects falling downward toward Earth and from no observations of objects falling upward away from Earth

1.4 What Is Science?  Scientific theories involve both inductive and deductive reasoning (continued)  Deductive reasoning is the process of generating hypotheses based on a well-supported generalization (such as a theory)  For example, based on the cell theory, any newly discovered organism would be expected to be composed of cells

1.4 What Is Science?  Scientific theories are formulated in ways that can potentially be disproved  Basic principles of science are referred to as theories because theories can be disproved or falsified  Falsifying theories is distinctly different between scientific theories and faith-based beliefs  “Each creature on Earth was separately created” cannot be subjected to scientific inquiry because it is a belief rooted in faith

1.4 What Is Science?  Science is a human endeavor  Human personality traits are part of “real science”  Scientists, like other people, may be driven by pride, ambition, or fear  Scientists sometimes make mistakes  Accidents, lucky guesses, intellectual powers, and controversies with others contribute strongly to scientific advances

1.4 What Is Science?  Science is a human endeavor (continued)  In the 1920s, bacteriologist Alexander Fleming grew bacteria in cultures  One of the bacterial cultures became contaminated with a mold  Fleming was about to destroy the culture when he noticed the mold (Penicillium) inhibited bacterial growth in the culture

1.4 What Is Science?  Science is a human endeavor (continued)  Fleming hypothesized that the mold produced an antibacterial substance  Further tests using broth from pure Penicillium cultures lead to the discovery of the first antibiotic, penicillin