Concept 1-5: Scientific inquiry
• Two approaches to science:
Discovery science
Inductive reasoning
Hypothesis-based science
aka “the scientific method”
Uses deductive reasoning
Discovery science
• Careful observations of natural phenomena
• Analysis of data
• Inductive reasoning
Generalization based on many observations.
• Theory based on these observations.
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Galapagos finches
• Darwin’s observations of
finches on the Galapagos
islands.
He spent 40 months taking
notes of nature while he
was a naturalist aboard the
HMS Beagle.
He derived his theory of
evolution from these
observations.
Discovery science vs. Scientific method
• Discovery science is not bad, but not very
robust.
Anecdotal observations are not hard evidence, but
can lead to experiments to robustly test the
hypotheses.
• The scientific method (hypothesis-based
science) is the only accepted way to obtain
hard evidence for a theory or hypothesis.
Hypothesis based science
Hypothesis
must be testable
must be falsifiable
Prediction:
Deductive reasoning
(“if….then”)
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Testing evolution theory
• If bacteria grows in an environment with
antibiotics, then after many generations the
bacteria will evolve antibiotic resistance.
• Experiment: compare the bacteria
Staphylococcus aureus antibiotic resistance
before and after penicillin was developed.
Evolution of MRSA
• Staphylococcus aureus was used by
Alexander Fleming in the development of
penicillin.
1943: nearly all S. aureus was killed by penicillin.
1950: 40% of S. aureus was antibiotic resistant.
1960: 80% of S. aureus was antibiotic resistant.
Today, 98% of S. aureus is resistant to penicillin.
MRSA = Methicillin resistant staphylococcus aureus.
Hypotheses
can never
be proved to
be correct.
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3rd hypothesis of flashlight problems
Evil flashlight fairies destroy flashlights.
The scientific method
• Step 1: Observation
• Step 2: Asking questions (develop hypotheses)
• Step 3: Make predictions
If_____________, then I expect ____________.
• Step 4: Design an experiment to test your
hypotheses.
• Step 5: Collect and Analyze data
• Step 6: Make conclusions based on your data.
Designing experiment
• Variables
Independent variable
The variable that you control during the experiment. A good
experiment should only have one independent variable.
Placed on the X-axis on graphs and tables.
Dependent variable
The variable that changes in response to the independent variable.
Placed on the Y-axis on graphs and tables.
Controlled variables
Alternative independent variables that you control so only your
chosen independent variable will affect the experiment.
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Designing an experiment
• Good experiments should always have replication
One experiment is not considered robust, especially if
sample size is small.
Results that are repeatable over several of same type of
experiments are more credible.
Large sample sizes are more statistically significant than
very small sample sizes.
• A good experiment should always have a
control
Independent variable is omitted or held constant.
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