1.2 Scientists form generalizations from observations The Nature of science FIGURE 1.3 Deductive reasoning: How Eratosthenes estimated the cir- Biology is a fascinating and important subject, because it cumference of the earth using deductive reasoning. 1. On a dramatically affects our daily lives and our futures. Many day when sunlight shone straight down a deep well at Syene in es, such as the worlds rapidly expanding population and diseases like cancer and AIDS. The knowledge these biolo- 2. The shadow's length and the obelisk,'s height formed two sides of a triangle. Using the recently developed principles of Euclidean gists gain will be fundamental to our ability to manage the geometry, he calculated the angle, a, to be 7o and 12, exactly t of orlds resources in a suitable manner, to prevent or cure circle(360 ).3. If angle a= so of a circle, then the distance diseases, and to improve the quality of our lives and those between the obelisk(in Alexandria)and the well (in Syene)must of our children and grandchildren equal so of the circumference of the earth. 4. Eratosthenes had Biology is one of the most successful of the "natural sc heard that it was a 50-day camel trip from Alexandria to Syene ences, "explaining what our world is like. To understand Assuming that a camel travels about 18.5 kilometers per day, he biology, you must first understand the nature of science. estimated the distance between obelisk and well as 925 kilometers The basic tool a scientist uses is thought. To understand (using different units of the nature of science, it is useful to focus for a moment on measure, of course) how scientists think. They reason in two ways: deductively 5. Eratosthenes thus de- duced the circumference and inductively of the earth to be 50 x 25=46,250 Deductive reasoning kilometers. Modern Deductive reasoning applies general principles to predict distance from the well to obelisk specific results. Over 2200 years ago, the Greek Era the obelisk at just over Length of tosthenes used deductive reasoning to accurately estimate 800 kilometers. Employ he circumference of the earth. At high noon on the longest ing a distance of 800 day of the year, when the suns rays hit the bottom of a kilometers, Era deep well in the city of Syene, Egypt, Eratosthenes mea sosthenes,s value would sured the length of the shadow cast by a tall obelisk in Al ave been50×800= exandria. about 800 kilometers to the north. Because he 40.000 kilometers The actual circumference is knew the distance between the two cities and the height of 40.075 kilometers the obelisk, he was able to employ the principles of euclid ean geometry to correctly deduce the circumference of the earth(figure 1. 3). This sort of analysis of specific cases us- ing general principles is an example of deductive reasoning It is the reasoning of mathematics and philosophy and is used to test the validity of general ideas in all branches of knowledge. General principles are constructed and then used as the basis for examining specific cases. Inductive Reasoning you release an apple from your hand, what happens? The apple falls to the ground. From a host of simple, specific Inductive reasoning uses specific observations to construct observations like this, Newton inferred a general principle general scientific principles. Webster's Dictionary defines sci- all objects fall toward the center of the earth. What New ence as systematized knowledge derived from observation ton did was construct a mental model of how the world and experiment carried on to determine the principles un- works, a family of general principles consistent with what derlying what is being studied. In other words, a scientist he could see and learn. Scientists do the same today. They determines principles from observations, discovering gen- use specific observations to build general models, and then eral principles by careful examination of specific cases. In- test the models to see how well they work ductive reasoning first became important to science in the 1600s in Europe, when Francis Bacon, Isaac Newton, and Science is a way of viewing the world that focuses on others began to use the results of particular experiments to objective information, putting that information to work infer general principles about how the world operates. If to build understanding Part I The Origin of Living things6 Part I The Origin of Living Things The Nature of Science Biology is a fascinating and important subject, because it dramatically affects our daily lives and our futures. Many biologists are working on problems that critically affect our lives, such as the world’s rapidly expanding population and diseases like cancer and AIDS. The knowledge these biolo￾gists gain will be fundamental to our ability to manage the world’s resources in a suitable manner, to prevent or cure diseases, and to improve the quality of our lives and those of our children and grandchildren. Biology is one of the most successful of the “natural sci￾ences,” explaining what our world is like. To understand biology, you must first understand the nature of science. The basic tool a scientist uses is thought. To understand the nature of science, it is useful to focus for a moment on how scientists think. They reason in two ways: deductively and inductively. Deductive Reasoning Deductive reasoning applies general principles to predict specific results. Over 2200 years ago, the Greek Era￾tosthenes used deductive reasoning to accurately estimate the circumference of the earth. At high noon on the longest day of the year, when the sun’s rays hit the bottom of a deep well in the city of Syene, Egypt, Eratosthenes mea￾sured the length of the shadow cast by a tall obelisk in Al￾exandria, about 800 kilometers to the north. Because he knew the distance between the two cities and the height of the obelisk, he was able to employ the principles of Euclid￾ean geometry to correctly deduce the circumference of the earth (figure 1.3). This sort of analysis of specific cases us￾ing general principles is an example of deductive reasoning. It is the reasoning of mathematics and philosophy and is used to test the validity of general ideas in all branches of knowledge. General principles are constructed and then used as the basis for examining specific cases. Inductive Reasoning Inductive reasoning uses specific observations to construct general scientific principles. Webster’s Dictionary defines sci￾ence as systematized knowledge derived from observation and experiment carried on to determine the principles un￾derlying what is being studied. In other words, a scientist determines principles from observations, discovering gen￾eral principles by careful examination of specific cases. In￾ductive reasoning first became important to science in the 1600s in Europe, when Francis Bacon, Isaac Newton, and others began to use the results of particular experiments to infer general principles about how the world operates. If you release an apple from your hand, what happens? The apple falls to the ground. From a host of simple, specific observations like this, Newton inferred a general principle: all objects fall toward the center of the earth. What New￾ton did was construct a mental model of how the world works, a family of general principles consistent with what he could see and learn. Scientists do the same today. They use specific observations to build general models, and then test the models to see how well they work. Science is a way of viewing the world that focuses on objective information, putting that information to work to build understanding. 1.2 Scientists form generalizations from observations. FIGURE 1.3 Deductive reasoning: How Eratosthenes estimated the cir￾cumference of the earth using deductive reasoning. 1. On a day when sunlight shone straight down a deep well at Syene in Egypt, Eratosthenes measured the length of the shadow cast by a tall obelisk in the city of Alexandria, about 800 kilometers away. 2. The shadow’s length and the obelisk’s height formed two sides of a triangle. Using the recently developed principles of Euclidean geometry, he calculated the angle, a, to be 7° and 12′, exactly 1 50 of a circle (360°). 3. If angle a = 1 50 of a circle, then the distance between the obelisk (in Alexandria) and the well (in Syene) must equal 1 50 of the circumference of the earth. 4. Eratosthenes had heard that it was a 50-day camel trip from Alexandria to Syene. Assuming that a camel travels about 18.5 kilometers per day, he estimated the distance between obelisk and well as 925 kilometers (using different units of measure, of course). 5. Eratosthenes thus de￾duced the circumference of the earth to be 50 925 46,250 kilometers. Modern measurements put the distance from the well to the obelisk at just over 800 kilometers. Employ￾ing a distance of 800 kilometers, Era￾tosthenes’s value would have been 50 × 800 40,000 kilometers. The actual circumference is 40,075 kilometers. Sunlight at midday c D iti is e t s anc = 8 e 0 between 0 km Well Light rays parallel Height of obelisk Length of shadow a a