THE SCIENTIFIC METHOD
Common Fallacies
“don’t get wet on a cold day”
If these two events occur close to each other, is that proof that
the first event caused the second?
No! -- There is no direct evidence that getting wet on a chilly
day causes a cold.
Colds are more common in chilly weather because the cold
drives people inside
-also, peoples mucous membranes dry, exposing cells to
the virus
Anecdotal evidence: information based on personal
experience and testimonials.
-coincidence
-clustered by underlining causes (fire house)
Toads cause warts
Too many variables:
-exposed to people with warts
-exposed to surfaces with wart causing viruses
Anecdotal evidence can be a starting point for forming a
hypothesis
Inductive vs Deductive Reasoning
Hypothesis = proposed explanation whose validity can be
tested.
1) must be consistent with all observations collected
2) must be testable
-”frogs cause warts” is testable
-”elves cause warts” is not
-should be able to make predictions
1600s -- the beginning of experimentation
-diseases were caused by gods
-people got diseases by sex
-sex must be immoral
Inductive reasoning - accumulation of data and facts and
makes a hypothesis
-use facts to arrive at a possible explanation of an
observed phenomenon.
“are the observed events best explained by this
hypothesis or another”
-AIDS (HIV or amylnitrate)
Deductive reasoning
makes predictions (“if . . then . . “ statements”)
“if this hypothesis is valid, then certain specific events can be
expected to occur”
Inductive - specific to general (organisms composed of cells)
Deduction - general to specific
(if all organisms are composed of cells, and humans are
organisms, then humans are composed of cells)
Testing the Hypothesis
-experimental design
Use controlled experiments to test a hypothesis
-Only one condition is varied
Experimental group
Control group
handles toads
handles frogs (placeba)
4/100
3/100
placebo = substitute for the variable which is known to have no
effect
-without placebo, there would be two variables (not
handling frogs -- knowledge)
Experimental variable - component of the experiment being
tested
Dependent variable - result or change that occurs due to the
experimental variable
Saccharine studies in mice
inbred, water, temperature, sex, light
Experimental and Dependent variable
-collecting data
should be quantitative
-one group was more wartier than the other
-3% of frog handlers and 4% of toad handlers got warts
-observation
observational data is also data
(observe, hypothesize, predict, collect data (observation)
hens (major and minor)
-fire / incubation temperature / predators
-interpretation
data fails to support the hypothesis (3 and 4% are not
significantly different)
Statistics
cannot conclude that toads never cause cancer under any
circumstances.
-are scratches necessary
-try every type of toad (repetitive / tedium)
Avoid faulty reasoning:
After training the flea for many months, the biologist was able
to get a response to certain commands. The most gratifying of
the experiments was the one in which the professor would shout
the command “jump”, and the flea would leap into the air each
time the command was given.
The professor was about to submit this remarkable feat to
posterity via a scientific journal, but he -- in the manner of the true
scientist -- decided to take his experiments one step further. He
sought to determine the location of the receptor organ involved.
In one experiment, he removed the legs of the flea, one at a time.
The flea obligingly continued to jump on command, but as each
successive leg was removed, its jumps became less spectacular.
Finally, with the removal of its last leg, the flea remained
motionless. Time after time the command failed to get the usual
response.
The professor decided that at last he could publish his
findings. He set pen to paper and described in meticulous detail
the experiments executed over the preceding months. His
conclusion was one intended to startle the scientific world: When
the legs of a flea are removed, the flea can no longer hear.”
Presenting the Data
published as an original research article
evaluate, confirm, repeat
-garlic breath
negative data is not no data
An example
Identical twins sleeping in their 1 PM history class
-big lunch
-too warm
-sit in back
-boring teacher
-stayed up too late
Scott skipped lunch / Scott sat in front (tested one at time)
Twin was control
“Scott fell asleep because the devil made him”
Guppies
Killfish - prey on small guppies
-guppies grow large
-once mature, they breed several times with small broods
Pike - prey on large, sexually mature larvae
-smaller adults
-breed young with large brood
Cause and Effect
Hypothesis 1 - Physical environment
Hypothesis 2 - Predator
11 years / 60 generations
Theories / Laws
If the data does not support a hypothesis, the hypothesis must
be discarded or modified.
Data can support a hypothesis, not prove it.
“knowing that some future observation and / or experiment
might falsify the hypothesis, a scientist never says that the
data “proves” the hypothesis”
If overwhelmingly supported by a large body of evidence and
hypothesis can become a theory.
A theory is not a fuzzy or weak guess.
Unifying theories versus facts
(Darwin / Einstein)
4 THEORIES
Cell theory
-all organisms are composed of cells
unicellular
multicellular
colonial
Robert Hooke (1665) cork cells at 30 X
Antonie van Leeuwenhoek - ground glass with sand (300 X)
Matthias Schleiden and Theodor Schwann
-cells come from other cells
EM
eucaryote / procaryote
cells have membranes and DNA and ribosomes
cell walls and size (0.1 mm to 1,000 mm)
Biogenesis
Life comes only from life
Evolution
All living things have a common ancestor and are adapted to a
particular way of life
Diversity and Unity
260,000 plants, 50,000 vertebrates, 750,000 insects
5 - 30 million species
-grouping (pine tree)
Unity = DNA / Respiration / cell structure
Kingdom, phylum, class, order, family, genus, species
6 Kingdoms
archeobacteria
eubacteria
protists - unicellular eucaryotes
fungi - decomposers
plants - solar radiation
animals - ingest food
horse and zebra
rabbits / humans - other mammals
birds / alligator - other vertebrates
bacteria (3 billion years ago)
Charles Darwin
-descent with modification (evolution)
-natural selection (mechanism of evolution)
Explains Unity and Diversity
Gene theory
Organisms contain coded information that dictates their form,
function, and behaviour.
Form and function are encoded in DNA
proteins / phenotype / genotype
-genetic code is same for all organisms
-pass on their DNA (offspring)
asexual
sexual
What science shouldn’t do
-Any one of us can perform a controlled experiment to
determine if a food additive is safe.
fully natural causes
past / present / and future (theories and principles) / place
Doctrins of creation, which have a mythical, philosophical or
theological basis, are not part of science because they are
not subject to objective observations and experimentation by
all persons
When faith is involved, a hypothesis is not subjected to being
proven false in a purely objective way.
Ethical and moral decisions
“good versus bad” research
how science is used
(fetal research, genetic engineering, atomic energy)
-education of the general public is necessary
-discovering something no one else knows
Science and technology are related
= apply discovery of science
Watson and Crick (DNA structure) - genetic engineering of
insulin
“Technology should be watched closely, monitored, criticized,
even voted in or out by our electorate, but science itself must
be given its head if we want it to work”
Technology can be a double edge sword.
-medicine keeps people healthy
-human population has grown 10-fold in 100 years
-acid rain
-deforstation
-global warming
-nuclear accidents
-ozone holes
-toxic waste
-extinction
-politics, economics, culture, values