“The” Scientific Method (chapter 1
of text)
Observation/Question about the World
Hypothesis
Predictions based on hypothesis
Test
Evaluate results
Generate new hypotheses and repeat
process.
Observation/Question
First step.
E.g. It looks as if the coastlines of South
America and Africa would fit together.
Why might that be?
Wasps have yellow and black striped bodies
that make them conspicuous. Is there an
advantage for wasps in being brightly
colored?
Hypothesis
The hypothesis is a tentative
EXPLANATION for your observations or
an ANSWER to your question.
In generating a hypothesis you would use
your knowledge of the subject to make an
“educated guess” as to what the correct
hypothesis is.
Hypothesis
For example:
Wasps are brightly colored because it
signals that they are dangerous. This deters
predators from attacking them.
Hypothesis
Scientific hypotheses are TENTATIVE
explanations for your observations.
A hypothesis must be modified if new
evidence contradicts it.
Hypothesis
Hypotheses must be TESTABLE.
“The devil made wasps black and yellow”
depends on a supernatural explanation and
so is untestable.
You must be able to generate testable
predictions
Definition of a hypothesis
Putting it all together we get a workable
definition of a hypothesis:
A hypothesis is a tentative, testable
explanation for your observations.
Prediction
Hypotheses are tested by generating
predictions based on the hypotheses and
testing them.
Predictions about wasp coloration?
Prediction
E.g. If wasps are protected by their color
pattern then changing their color pattern
should make them more vulnerable to
predators
Prediction
If wasp coloration provides protection then
giving that coloration to non-stinging
insects should provide them with protection.
Prediction
Notice that predictions generally take the
form of an IF THEN statement.
IF something is true THEN something else
must follow.
Test
Predictions must be tested.
If testable predictions cannot be generated
an hypothesis is not useful and probably not
a scientific hypothesis.
Testing predictions
Predictions may be tested through
(i) observational/natural experiments or (ii)
manipulative experiments
Observational/natural experiments usually
carried out when it is impossible or
unethical to carry out a manipulative
experiment.
Unethical experiments
Examples of unethical experiments?
Unethical experiments
When potentially severe harm is done to
participants. (e.g. compelling people to
smoke to assess effects of tobacco smoke on
lung function).
Observational/natural experiment
In such experiments data are collected that
allow us to test predictions, but the study
subjects are not directly manipulated.
E.g. Collect medical histories of people and
make comparisons between groups (e.g.
smokers and non-smokers, males and
females, miners and non-miners, etc.).
Observational/natural experiment
Weakness of natural experiments include
(i) difficulty separating cause and effect
relationships. Correlation does not imply
causation.
Observational/natural experiment
E.g. Predict that a male bird will mate more
often because he has a long tail, which
makes him attractive to females.
We find a positive relationship between male
tail length and how often he mates.
Can we conclude that having a long tail
increases mating frequency?
Observational/natural experiment
No, because we can’t rule out possibility
that mating frequently causes his tail to
grow longer.
Observational/natural experiment
In the Netherlands there is a strong
correlation between the number of stork
nests on a house and the number of
children in the house.
Do storks bring babies?
Observational/natural experiment
Sadly no!
Larger houses have more chimneys for
storks to use as nest sites and large families
need large houses.
Manipulative experiments
Most powerful way to test predictions is
with a manipulative experiment.
We can focus on the one factor we think is
important and manipulate it.
Design of experiments
To test whether wasp coloration provides
protection we need to devise an
experimental manipulation.
E.g. We could paint over the yellow parts
of a wasp’s body to make it all black and
see if predators attack it.
Experiments
Would this be an adequate experiment?
Experiments
We have nothing to compare our results to. How
do we know if predators are more or less likely
attack our manipulated wasp?
Sample size of one doesn’t tell us much. Need
large enough experimental and control groups for
meaningful statistical analysis.
What do we need?
Controls
We need a CONTROL group of wasps that
have not been manipulated to compare our
group of manipulated wasps to.
Characteristics of control group
Control group should be treated exactly the
same as the experimental group except that
they don’t receive the treatment.
There should be only ONE difference between
the groups.
Controls
Would a group of unpainted wasps be a
good control?
Controls
Pretty good, but could be better.
Also need to control for possible effects of
handling wasps to paint them and the
presence of paint on the wasps in addition
to the change in appearance of wasps.
Controls
Better control might be to paint wasps in
clear paint. Then only difference between
groups would be the appearance of the
control and experimental groups.
Best approach to have two control groups
one unmanipulated and one painted with
clear paint.
Evaluate results
After carrying out the experiment we would
analyze the results to see if they support or
contradict our hypothesis.
Evaluate results
A positive result does not “prove” our
hypothesis.
You cannot ever prove a hypothesis is true
because it is subject to revision if new
evidence is presented.
Evaluate results
However, we can become increasingly
confident in hypotheses that resist repeated
attempts to falsify them.
The more often we test a hypothesis the
more likely that the hypothesis is “true.”
Generate new hypotheses and
repeat process
Results of experiments may falsify
hypothesis and so new hypotheses must be
produced and the process continues.
Process of science is an ongoing one with
frequent testing of ideas.
Discovery or descriptive science
Hypothesis-testing not only way science
proceeds. “The” scientific method not true.
Careful observation and collection of data
can build up our understanding of the
world.
Discovery or descriptive science
For example, sequencing of the human
genome does not involve hypothesis testing
nor does describing the behavior of a bird or
mapping the distribution of a plant, but all
add to human knowledge.
Discovery or descriptive science
Descriptive science can lead to important
conclusions by a process of generalizing
from many observations (inductive
reasoning).
E.g. all organisms are made of cells.
“What goes up must come down.”
Science and Culture
It is important to remember that science is a
human endeavor that is not “pure” and
immune from external influences.
The questions that people ask or think that
are worth asking are strongly influenced by
upbringing, culture and experience.
Science and Culture
For example, in studying mating behavior in
animals until the 1970’s most scientist’s
focused on the importance of male-male
competition in determining mating success.
Male impala and elephant seals fighting
over females
Science and Culture
It wasn’t until large numbers of female
scientists began working in the field that the
importance of female choice of mates was
recognized as being of major significance.
Choosy female ruffs mate
with only the most
impressive males
Science and Culture
Our assumptions about how the world
works are also shaped by culture.
Important to be aware that numerous
assumptions (conscious and unconscious)
underlie our thinking.
What is an assumption?
Assumptions
An assumption is a fact or piece of information
you take to be true as a starting point in research.
E.g. testing drugs on mice to see how well the
drugs work is based on the assumption that mice
and humans are biologically similar and that the
drugs will work in a similar manner in each
organism.
Assumptions
Assumptions may prove to be invalid which can
severely limit the usefulness of a piece of
research.
For example, a lot of medical research has been
carried out on men, but not women based on the
assumption that male and female bodies behaved
similarly. In many cases the assumption is invalid.
For more information see e.g.
http://magee.upmc.com/WomenHealth.htm
Limits of Science
Science requires that hypotheses be testable
and falsifiable and that observations and
experiments be repeatable.
Science seeks natural causes for natural
phenomena.
Limits of Science
Science cannot support or falsify
hypotheses that supernatural forces cause,
for example, storms or illness because such
claims are not testable.
Limits of Science
Occam’s Razor: the principle that a simple
explanation is better than more complex
ones.
As we gain more and more understanding of
the causes of storms and disease there is no
need to invoke supernatural explanations
because simpler explanations are sufficient.
Creationism and “Intelligent Design”
The idea of evolution has been harshly criticized
by religious fundamentalists since the publication
of the Origin in 1859.
This has been especially true in the U.S.
Repeatedly, believers in the literal truth of the
Bible have attempted to have alternatives to
evolution (i.e., creationism) taught in the public
schools and to have the teaching of evolution
either banned or restricted.
Creationism and “Intelligent Design”
The U.S. Supreme Court has prohibited the
teaching of creationism in public schools as
a violation of the establishment of religion
clause of the Constitution.
Latest attempt to insert creationism into
schools is the idea of “Intelligent Design.”
Creationism and “Intelligent Design”
The concept of “intelligent design” is outlined
most clearly in Michael Behe’s book “Darwin’s
Black Box.”
The central idea in “intelligent design” is that
some structures in the body are so complex that
they could not possibly have evolved by a gradual
process of natural selection. These structures are
said to “irreducibly complex.”
Creationism and “Intelligent Design”
By “irreducibly complex” Behe means that
a complex structure cannot be broken down
into components that are themselves
functional and that the structure must have
come into existence in its complete form.
Creationism and “Intelligent Design”
If structures are “irreducibly complex” Behe
claims that they cannot have evolved. Thus,
their existence implies they must have been
created by a designer (i.e. God, although the
designer is not explicitly referred to as
such).
Creationism and “Intelligent Design”
Behe’s main examples are various
biochemical pathways in the body, the
blood clotting system, and structures such
as the bacterial flagellum.
Creationism and “Intelligent Design”
Since the publication of Behe’s book, it has
been demonstrated repeatedly that things he
has claimed to be irreducibly complex are
not in fact so.
E.g. the flagellum in eel sperm lacks several
of the components found in other flagella,
yet the flagellum functions well.
Creationism and “Intelligent Design”
The blood clotting system in dolphins lacks
at least one component that the human
system has, yet it too is functional.
In addition, plausible gradual scenarios for
the evolution of biochemical pathways
including the Kreb’s cycle have been
documented.
Creationism and “Intelligent Design”
“Intelligent design” fails as a scientific
hypothesis because it is unfalsifiable.
It also fails the test of Occam’s Razor
because the principal mechanism of
evolution (i.e. natural selection) more
simply explains the complexity of living
things.
Theory
Everyday use of the word theory is different from
its use in science.
A scientific theory is
(i) much more general explanation than a
hypothesis
(ii) can be used to generate a large number of
narrower hypotheses and
(iii) usually supported by a very large body of
supporting evidence.
Theory
For example theory of gravitation explains the
movements of planets and stars, tidal movements,
and why and how objects fall and many other
physical phenomena.
Theory of evolution explains presence of fossils,
behavior of organisms and antibiotic resistance in
bacteria and many other biological phenomena