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Progress in science
consists of the development of better explanations for the causes of
natural phenomena. Scientists never can be sure that a given
explanation is complete and final. Some of the hypotheses advanced by
scientists turn out to be incorrect when tested by further observations
or experiments. Yet many scientific explanations have been so
thoroughly tested and confirmed that they are held with great
confidence.
The theory of evolution
is one of these well-established explanations. An enormous amount of
scientific investigation since the mid-19th century has converted early
ideas about evolution proposed by Darwin and others into a strong and
well-supported theory. Today, evolution is an extremely active field of
research, with an abundance of new discoveries that are continually
increasing our understanding of how evolution occurs.
This booklet considers
the science that supports the theory of evolution, focusing on three
categories of scientific evidence:
- Evidence for the origins of the universe, Earth, and life
- Evidence for biological evolution, including findings from
paleontology, comparative anatomy, biogeography, embryology,
and molecular biology
- Evidence for human evolution
At the end of each of
these sections, the positions held by advocates of "creation science"
are briefly presented and analyzed as well.
The theory of evolution
has become the central unifying concept of biology and is a critical
component of many related scientific disciplines. In contrast, the
claims of creation science lack empirical support and cannot be
meaningfully tested. These observations lead to two fundamental
conclusions: the teaching of evolution should be an integral part of
science instruction, and creation science is in fact not science and
should not be presented as such in science classes.
Terms Used in Describing the
Nature of Science*
Fact: In science, an observation that has been repeatedly
confirmed and for all practical purposes is accepted as "true." Truth
in science, however, is never final, and what is accepted as a fact
today may be modified or even discarded tomorrow.
Hypothesis: A tentative statement about the natural world
leading to deductions that can be tested. If the deductions are
verified, the hypothesis is provisionally corroborated. If
the deductions are incorrect, the original hypothesis is proved false and
must be abandoned
or modified. Hypotheses can be used to build more complex inferences
and explanations.
Law: A descriptive generalization about how some aspect of the
natural world behaves under stated circumstances.
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Theory: In science, a well-substantiated explanation of some
aspect of the natural world that can incorporate facts, laws,
inferences, and tested hypotheses.
The contention that evolution should be taught as a "theory, not as a
fact" confuses the common use of these words with the scientific use.
In science, theories do not turn into facts through the accumulation of
evidence. Rather, theories are the end points of science. They are
understandings that develop from extensive observation, experimentation,
and creative reflection. They incorporate a large body of scientific
facts, laws, tested hypotheses, and logical inferences. In this sense,
evolution is one of the strongest and most useful scientific theories we
have.
*Adapted from
Teaching About Evolution and the Nature of Science by the
National Academy of Sciences (Washington, D.C.: National Academy Press,
1998).
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