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Learning How To Do Science Frontiers in Science Presentation
Fred C. Dyer Department of Zoology 3/12/2011
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Doing Science Elements of the scientific method: Observe patterns
2. Ask questions 3. Formulate hypotheses that make specific predictions Perform experiments or observations to test hypotheses Analyze Data
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Starting a scientific inquiry…. Inheritance
Offspring tend to resemble their parents F Galton (1886): inheritance of height What do parents and offspring have in common? features_section/ / iraq.asp
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Starting Point: OBSERVATIONS
Description of PATTERN and PROCESS You see a pattern in nature You also observe other information that may help you understand the processes underlying it To understand processes, ask focused QUESTIONS
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Asking Questions Watch video and write down at least 3 questions about what you see archer fish
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Refining questions about pattern
Sometimes it helps first to find out more details about the thing we are trying to understand: Often this involves asking quantitative questions Not just whether archer fish eat only insects, but what percentage of their diet of insects Not just whether archer fish sometimes feed alone, but what is the distribution of group sizes when fish are feeding Also: What percentage of times do fish jump vs. shoot? What is success rate for jumping vs. shooting? Just how accurate are It may also be useful to ask qualitative questions For example: make a detailed list of the prey types that the animal feeds on, or the habitats where it feeds
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Answering the questions
Formulate hypotheses: A hypothesis is a plausible guess as to answer Hypotheses are in the form of statements Usually it is possible to generate several reasonable hypotheses Why do archer fish sometimes jump and sometimes shoot? Write down at least three distinct hypotheses that would answer that question
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Steps so far: Observations: the patterns/puzzles we see Questions: what processes may explain these patterns? Hypotheses: statements of possible answers Next Step: TESTING hypotheses
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Testing Hypotheses A hypothesis is a guess about an explanation for a phenomenon To “explain” something means you understand the cause What does it mean to say that A causes B? It means that B’s occurrence depends upon A occurring It also means that there is some material connection that mediates the causal relationship between A and B Testing a hypothesis means gathering evidence to determine whether the hypothesis is correct.
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Logic of Hypothesis Testing
Here’s the logic: Formulate hypothesis, e.g. H1: “A causes B”: Determine the predictions that this hypothesis makes. For example, if Hypothesis 1 is correct, then every time A occurs, B should occur, and B never occurs without A occurring Perform additional observations to determine whether predictions are upheld. The observations may be aided by doing experiments that control the variables of interest (though sometimes experiments aren’t possible).
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Steps so far…. In the following example, write down:
Observations about particular natural patterns Questions about the causes/explanations for these patterns Hypotheses about the possible causes of the phenomenon Predictions that each hypothesis makes if it is true An additional observation or experiment that you could do that would allow you to test this prediction
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Why do archer fish sometimes jump and sometimes shoot?
Example: Why do archer fish sometimes jump and sometimes shoot? Some hypotheses to consider: Height of prey Whether prey is moving Experience of predator Whether predator is in a group Pick ONE of these and propose a test
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Generalizations About Scientific Hypotheses
A good hypothesis: Is consistent with other known facts about nature Can potentially be falsified (proven wrong) Uncertainty always exists: You can’t prove a hypothesis right, you can only fail to falsify it: other hypotheses might make same prediction But you may not be able to falsify it with absolute certainty: failure to see effect predicted by hypothesis may occur because experimental conditions weren’t present Value of considering multiple hypotheses: There are often multiple causes for phenomena Considering multiple causes helps in designing experimental controls
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An aside… Hypothesis vs. Theory
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Much scientific evidence is indirect
Some difficulties that make science hard or confusing Applying scientific method to the past: what is role of “prediction” and nature of evidence for testing these predictions? Much scientific evidence is indirect Patterns of causation: multiple direct or indirect causes may explain phenomena Some hypotheses are represented as complex computational functions
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Difficulty 1: Hypotheses about the past
E.g., when did dinosaurs live; why did they go extinct? Common view of science: repeatable observations controlled experiments (perhaps replicated many times) test hypotheses by making predictions about outcome of experiments How can one do science when dealing with unique past events?
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Dealing with unique past events
Suggest some hypotheses, and the predictions of these hypotheses The pattern (ie. the evidence): A body with a gunshot wound to the temple A revolver on the floor near the body The question: whodunit?
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Number of families (types) of marine invertebrates
Mass extinctions as a “whodunit” Why do mass extinctions happen? Number of families (types) of marine invertebrates Event that wiped out dinosaurs Mass extinctions Total number of families of marine invertebrates over 600 million years Background extinction rate
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What killed the dinosaurs?
H1: Climate change caused by terrestrial processes H2: Extra-terrestrial impact by asteroid Basis of H2: Iridium in some sediments deposited around the time of extinction) Other predictions: Iridium found worldwide Shocked quartz in same sediments Impact crater THESE ARE PREDICTIONS ABOUT FUTURE OBSERVATIONS
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Difficulty 2: indirect evidence
Some processes happen on a scale that is too small, too fast, too large, or two slow for direct observation, and so observations are mediated by instruments or indirect measures Also, a LOT of scientific observations are based on testimony of other experts—importance of trust
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Difficulty 3: Multiple causes
We’re interested in causes, but….. All we can really see are correlations among events or objects Multiple causes may explain given correlation Example: diet and cancer Observations: Japanese have lower incidence of colon cancer than Americans, and have less (and different) fat in their diets H1: type and amount of fat in diet is cause of cancer Correlation between diet and cancer rate doesn’t prove causation Other hypotheses may explain the same pattern -- SUCH AS?
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Difficulty 3: Multiple causes (cont’d)
Example: diet and cancer Proving that a high fat diet increases likelihood of colon cancer doesn’t rule out possibility that other factors also cause colon cancer Proving that a high fat diet increases the likelihood of colon cancer doesn’t mean that a high fat diet will necessarily lead to colon cancer In both cases, diet may be only one of several factors leading to cancer (or preventing it)
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Hypotheses formulated as computational models
Difficulty 4: Hypotheses formulated as computational models Patterns: Direct evidence earth is warming…
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Global Warming: direct and reconstructed
Patterns: …and warming is recent Earth’s temperature changes inferred from actual measurements or indirect evidence (e.g., air bubbles in ice cores; glacial structure)
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What causes warming? H1: Natural “drivers” Solar irradiance
Actual Predicted H1: Natural “drivers” Solar irradiance Volcanic gases Gases from forest fires Gases from decomposition H2: Natural + anthropogenic drivers Gases from burning of carbon-based fuels Digestive gases from livestock and humans Test by building mathematical models that predict temperature given specific inputs
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