We accept today that science follows certain rules
and processes that make it a dependable source of information, but
those rules have not always been in place. Until as recently
as the 1600s, for instance, it was widely believed that living
things could arise spontaneously from non-living, dead, or waste
materials (this is called
because people saw such materials "generate" living
things such as mold or maggots, and no one thought to test whether this
was truly what was happening. In 1688, Italian
naturalist Francisco Redi set out to test the idea with decaying
meat in two containers: one open to the air, the other
sealed. The open container meat eventually became infested
with maggots. And when critics insisted that it was the
sealing of the second container that kept spontaneous generation
from occurring, Redi did the test with an open container and one
covered with cheesecloth, through which air could circulate (he
suspected what we now know, that flies were the actual source of the
maggots), and the cheesecloth-covered sample produced no
maggots. However, even as certain aspects of spontaneous
generation became recognized as
wrong, later, when germs were first
discovered, it was first thought that they were a spontaneous
product of sick tissues, rather than independent-living organisms
that reproduced in the body.
How research "killed" spontaneous generation.
More on Redi's experiments (Blog post).
Someone recreates the maggot experiment (Day One Video).
It was a long road from that basic test to
method, but some of the approach Redi used
persists: modern science is about testing suspected
explanations of ones observations, which can be
made directly through ones own personal senses or indirectly
through instruments or second-hand from someone else's direct
observations. An explanation for one or more observations is
properly called a hypothesis. A hypothesis
should produce testable predictions or it isn't much
use scientifically, and the tests are most reliably done under controlled
conditions. One hypothesis that always exists says that the
current hypothesis is wrong, which can also be confirmed by
testing - this concept is called the null hypothesis.
Introduction to scientific method.
A silly song, but it's got the bits in it.
In biology, complete control over conditions is
hard to achieve, but scientists still strive for it. If no
alternative exists, testing may be done as field studies, with
well-planned and organized series of observations that look for
evidence for the hypothesis predictions. Controlled
experiments may be done in a laboratory environment with
different test groups, similar to how Redi did his
experiment. One group, the experimental group,
is specifically set up to test some critical aspect (the variable,
or the independent variable)
of the hypothesis; another group, the control group,
duplicates the experimental group but removes the variable (or, if
that isn't possible, changes it in some significant way). In Redi's
second test, the experimental group was the cloth-covered containers (the
cloth barrier as a test of air access but fly blockage was the variable),
with the control test being containers with no cloth over them.
One expects there to be a critical difference in the results to uphold the
hypothesis - that difference is sometimes called the dependent
There are courses specifically in field study
Parts of an experiment (video - slides with explanation).
usually in some sort of number form (quantitative data,
as oppose to non-number qualitative data) are
collected from each group and compared. The
comparison is absolutely critical - just running an experimental
group is possible (we could give a new headache remedy to a group
of 100 people with headaches and record how much their symptoms
improved), but how would you know whether your results were
directly connected to your variable - how many headaches would have
improved on their own, or improved just because the subjects were
given a pill and expected improvement? Improvement based solely on
expectations is called the placebo effect, placebo
being an "empty" treatment - that makes it a confounding factor,
discussed below. In a proper
experiment, a control group would have been treated identically,
given "identical" pills with the remedy ingredient removed; the
difference in effects in the two groups can be said to be an
effect of the ingredient itself. Placebo effect is considered an
artifact, a result of one type of confounding factor, discussed
below. When a result arises from the way that a test is done,
but isn't actually connected to the variable, that result is called an
Quantitative methods (video).
about making qualitative data - ancient texts - quantitative for
the placebo effect.
Why is the placebo effect
stronger now than it used to be?