Biology (Holt)

Scientific Explanations
Scientific progress is made the same way a marble statue is, by chip-
ping away the unwanted bits. If a hypothesis does not provide
reasonable explanation for what has been observed, the hypothesis
must be rejected. Harte was able to show that enough acid was being
introduced into the ponds to kill the salamander embryos. His
hypothesis—that acid from melting snow was killing the salaman-
ders—was therefore supported. Scientists routinely make predictions
and attempt to confirm them by testing one or more hypotheses. The
hypothesis that acid rain is contributing to the loss of amphibian popu-
lations will require much more evidence before becoming accepted as
a broader theory.
It is important in science not to be misled by an isolated observa-
tion. Only after many studies like Harte’s will scientists be able to
assemble a picture that accurately reveals what is harming the
amphibians. As you have just read, other environmental factors may
play important roles. Figure 19 summarizes the steps in the devel-
opment of a theory. A is a set of related hypotheses that have
been tested and confirmed many times by many scientists. A theory
unites and explains a broad range of observations.

Constructing a Theory

Constructing a theory often involves considering contrasting ideas and
conflicting hypotheses. For example, Harte’s conclusions have been
questioned by scientists who suggest that his observations may be only
coincidence. Argument, disagreement, and unresolved questions are a
healthy part of scientific research, a true reflection of how science is
done. Scientists routinely evaluate one another’s work. A key require-
ment of valid scientific research is that it can be replicated—that is,
reproduced—by other scientists.
As you study biology, it is important to remember that
the word theoryis used very differently by scientists than by
the general public. To scientists, a theory represents that of
which they are most certain. In contrast to the general pub-
lic, theorymay imply a lack of knowledge, a guess. How
often have you heard someone say, “It’s only a theory” to
imply lack of certainty? As you can imagine, confusion
often results. In this textbook, the word theorywill always
be used in its scientific sense—that is, a theory is a gener-
ally accepted scientific principle.
There is, however, no absolute certainty in a scientific
theory. The possibility always remains that future evidence
will cause a scientific theory to be revised or rejected. A
scientist’s acceptance of a theory is always provisional.
Once a scientist completes an investigation, he or she
often writes a report for publication in a scientific jour-
nal. Before publication, the research report is reviewed
by other scientists. These reviewers ensure that the inves-
tigation was carried out with the appropriate controls,

theory

SECTION 3Scientific Processes 19

Questions

Theory

Predictions and hypotheses

Experimentation

Related

hypotheses are

verified by many.

Some

hypotheses

are supported.

Some

hypotheses

are rejected.

Scientists build theories

from questions, predic-

tions, hypotheses, and the

findings of their experi-

ments. When related

hypotheses consistently

explain scientific events, a

theory is formed.

Figure 19 Theories