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[The Talk.Origins Archive]
Evolution is a Fact and a Theory Copyright 1993-1997 by Laurence Moran
[Last Update: January 22, 1993]
When non-biologists talk about biological evolution they often confuse
two different aspects of the definition. On the one hand there is the
question of whether or not modern organisms have evolved from older
ancestral organisms or whether modern species are continuing to change
over time. On the other hand there are questions about the mechanism of
the observed changes... how did evolution occur? Biologists consider the
existence of biological evolution to be a fact. It can be demonstrated
today and the historical evidence for its occurrence in the past is
overwhelming. However, biologists readily admit that they are less
certain of the exact mechanism of evolution; there are several theories
of the mechanism of evolution. Stephen J. Gould has put this as well as
anyone else:
In the American vernacular, "theory" often means "imperfect fact" - part
of a hierarchy of confidence running downhill from fact to theory to
hypothesis to guess. Thus the power of the creationist argument:
evolution is "only" a theory and intense debate now rages about many
aspects of the theory. If evolution is worse than a fact, and scientists
can't even make up their minds about the theory, then what confidence can
we have in it? Indeed, President Reagan echoed this argument before an
evangelical group in Dallas when he said (in what I devoutly hope was
campaign rhetoric): "Well, it is a theory. It is a scientific theory
only, and it has in recent years been challenged in the world of science
- that is, not believed in the scientific community to be as infallible
as it once was."
Well evolution is a theory. It is also a fact. And facts and theories are
different things, not rungs in a hierarchy of increasing certainty. Facts
are the world's data. Theories are structures of ideas that explain and
interpret facts. Facts don't go away when scientists debate rival
theories to explain them. Einstein's theory of gravitation replaced
Newton's in this century, but apples didn't suspend themselves in midair,
pending the outcome. And humans evolved from ape-like ancestors whether
they did so by Darwin's proposed mechanism or by some other yet to be
discovered.
Moreover, "fact" doesn't mean "absolute certainty"; there ain't no such
animal in an exciting and complex world. The final proofs of logic and
mathematics flow deductively from stated premises and achieve certainty
only because they are NOT about the empirical world. Evolutionists make
no claim for perpetual truth, though creationists often do (and then
attack us falsely for a style of argument that they themselves favor). In
science "fact" can only mean "confirmed to such a degree that it would be
perverse to withhold provisional consent." I suppose that apples might
start to rise tomorrow, but the possibility does not merit equal time in
physics classrooms.
'Evolutionists have been very clear about this distinction of fact and
theory from the very beginning, if only because we have always
acknowledged how far we are from completely understanding the mechanisms
(theory) by which evolution (fact) occurred. Darwin continually
emphasized the difference between his two great and separate
accomplishments: establishing the fact of evolution, and proposing a
theory - natural selection - to explain the mechanism of evolution.'
- Stephen J. Gould, "Evolution as Fact and Theory"; Discover, May 1981
Gould is stating the prevailing view of the scientific community. In
other words, the experts on evolution consider it to be a fact. This is
not an idea that originated with Gould as the following quotations
indicate:
'Let me try to make crystal clear what is established beyond reasonable
doubt, and what needs further study, about evolution. Evolution as a
process that has always gone on in the history of the earth can be
doubted only by those who are ignorant of the evidence or are resistant
to evidence, owing to emotional blocks or to plain bigotry. By contrast,
the mechanisms that bring evolution about certainly need study and
clarification. There are no alternatives to evolution as history that can
withstand critical examination. Yet we are constantly learning new and
important facts about evolutionary mechanisms.'
- Theodosius Dobzhansky "Nothing in Biology Makes Sense Except in the
Light of Evolution", American Biology Teacher vol.35 (March 1973)
reprinted in Evolution versus Creationism, J. Peter Zetterberg ed., ORYX
Press, Phoenix AZ 1983
Also:
It is time for students of the evolutionary process, especially those who
have been misquoted and used by the creationists, to state clearly that
evolution is a FACT, not theory, and that what is at issue within biology
are questions of details of the process and the relative importance of
different mechanisms of evolution. It is a FACT that the earth with
liquid water, is more than 3.6 billion years old. It is a FACT that
cellular life has been around for at least half of that period and that
organized multicellular life is at least 800 million years old. It is a
FACT that major life forms now on earth were not at all represented in
the past. There were no birds or mammals 250 million years ago. It is a
FACT that major life forms of the past are no longer living. There used
to be dinosaurs and Pithecanthropus, and there are none now. It is a FACT
that all living forms come from previous living forms. Therefore, all
present forms of life arose from ancestral forms that were different.
Birds arose from nonbirds and humans from nonhumans. No person who
pretends to any understanding of the natural world can deny these facts
any more than she or he can deny that the earth is round, rotates on its
axis, and revolves around the sun.
'The controversies about evolution lie in the realm of the relative
importance of various forces in molding evolution.'
- R. C. Lewontin "Evolution/Creation Debate: A Time for Truth" Bioscience
31, 559 (1981) reprinted in Evolution versus Creationism, op cit.
This concept is also explained in introductory biology books that are
used in colleges and universities (and in some of the better high
schools). For example, in some of the best such textbooks we find:
'Today, nearly all biologists acknowledge that evolution is a fact. The
term THEORY is no longer appropriate except when referring to the various
models that attempt to explain HOW life evolves... it is important to
understand that the current questions about how life evolves in no way
implies any disagreement over the fact of evolution.'
- Neil A. Campbell, Biology 2nd ed., 1990, Benjamin/Cummings, p.434
Also:
'Since Darwin's time, massive additional evidence has accumulated
supporting the fact of evolution - that all living organisms present on
earth today have arisen from earlier forms in the course of earth's long
history. Indeed, all of modern biology is an affirmation of this
relatedness of the many species of living things and of their gradual
divergence from one another over the course of time. Since the
publication of The Origin of Species, the important question,
scientifically speaking, about evolution has not been whether it has
taken place. That is no longer an issue among the vast majority of modern
biologists. Today, the central and still fascinating questions for
biologists concern the mechanisms by which evolution occurs.'
- Helena Curtis and N. Sue Barnes, Biology 5th ed. 1989, Worth
Publishers, p.972
One of the best introductory books on evolution (as opposed to
introductory biology) is that by Douglas J. Futuyma, and he makes the
following comment:
'A few words need to be said about the "theory of evolution," which most
people take to mean the proposition that organisms have evolved from
common ancestors. In everyday speech, "theory" often means a hypothesis
or even a mere speculation. But in science, "theory" means "a statement
of what are held to be the general laws, principles, or causes of
something known or observed", as the Oxford English Dictionary defines
it. The theory of evolution is a body of interconnected statements about
natural selection and the other processes that are thought to cause
evolution, just as the atomic theory of chemistry and the Newtonian
theory of mechanics are bodies of statements that describe causes of
chemical and physical phenomena. In contrast, the statement that
organisms have descended with modifications from common ancestors - the
historical reality of evolution - is not a theory. It is a fact, as fully
as the fact of the earth's revolution about the sun. Like the
heliocentric solar system, evolution began as a hypothesis, and achieved
"facthood" as the evidence in its favor became so strong that no
knowledgeable and unbiased person could deny its reality. No biologist
today would think of submitting a paper entitled "New evidence for
evolution"; it simply has not been an issue for a century.'
- Douglas J. Futuyma, op. cit., p.15
There are readers of these newsgroups who reject evolution for religious
reasons. In general these readers oppose both the fact of evolution and
theories of mechanisms, although some anti-evolutionists have come to
realize that there is a difference between the two concepts. That is why
we see some leading anti-evolutionists admitting to the fact of
"microevolution" - they know that evolution can be demonstrated. These
readers will not be convinced of the "facthood" of (macro)evolution by
any logical argument and it is a waste of time to make the attempt. The
best that we can hope for is that they understand the argument that they
oppose. Even this simple hope is rarely fulfilled.
There are some readers who are not anti-evolutionist but still claim that
evolution is "only" a theory which can't be proven. This group needs to
distinguish between the fact that evolution occurs and the theory of the
mechanism of evolution.
We also need to distinguish between facts that are easy to demonstrate
and those that are more circumstantial. Examples of evolution that are
readily apparent include the fact that modern populations are evolving
and the fact that two closely related species share a common ancestor.
The evidence that Homo sapiens and chimpanzees share a recent common
ancestor falls into this category. There is so much evidence in support
of this aspect of primate evolution that it qualifies as a fact by any
common definition of the word "fact".
In other cases the available evidence is less strong. For example, the
relationships of some of the major phyla are still being worked out.
Also, the statement that all organisms have descended from a single
common ancestor is strongly supported by the available evidence, and
there is no opposing evidence. However, it is not yet appropriate to call
this a "fact" since there are reasonable alternatives.
Finally, there is an epistemological argument against evolution as fact.
Some readers of these newsgroups point out that nothing in science can
ever be "proven" and this includes evolution. According to this argument,
the probability that evolution is the correct explanation of life as we
know it may approach 99.9999...9% but it will never be 100%. Thus
evolution cannot be a fact. This kind of argument might be appropriate in
a philosophy class (it is essentially correct) but it won't do in the
real world. A "fact", as Stephen J. Gould pointed out (see above), means
something that is so highly probable that it would be silly not to accept
it. This point has also been made by others who contest the nit-picking
epistemologists.
The honest scientist, like the philosopher, will tell you that nothing
whatever can be or has been proved with fully 100% certainty, not even
that you or I exist, nor anyone except himself, since he might be
dreaming the whole thing. Thus there is no sharp line between
speculation, hypothesis, theory, principle, and fact, but only a
difference along a sliding scale, in the degree of probability of the
idea. When we say a thing is a fact, then, we only mean that its
probability is an extremely high one: so high that we are not bothered by
doubt about it and are ready to act accordingly. Now in this use of the
term fact, the only proper one, evolution is a fact. For the evidence in
favor of it is as voluminous, diverse, and convincing as in the case of
any other well established fact of science concerning the existence of
things that cannot be directly seen, such as atoms, neutrons, or solar
gravitation ....
'So enormous, ramifying, and consistent has the evidence for evolution
become that if anyone could now disprove it, I should have my conception
of the orderliness of the universe so shaken as to lead me to doubt even
my own existence. If you like, then, I will grant you that in an absolute
sense evolution is not a fact, or rather, that it is no more a fact than
that you are hearing or reading these words.'
- H. J. Muller, "One Hundred Years Without Darwin Are Enough" School
Science and Mathematics 59, 304-305. (1959) reprinted in Evolution versus
Creationism op cit.
In any meaningful sense evolution is a fact, but there are various
theories concerning the mechanism of evolution.
*****************
Wade T. Smith
morbius@channel1.com | "There ain't nothin' you
wade_smith@harvard.edu | shouldn't do to a god."
morbius@cyberwarped.com |
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