Author: Larry A. Moran (firstname.lastname@example.org)
Title: Evolution is a Fact and a Theory
EVOLUTION AS A FACT AND A THEORY
version 2.1 (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
it's 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
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
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 alterantives 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
"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 bology 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
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
Neil A. Campbell, BIOLOGY 2nd ed., 1990, Benjamin/Cummings, p.434
"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 constrast, 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
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
catagory. 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
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 consistant 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.
Laurence A. Moran (Larry)