Most scientists consider evolution a firmly supported theory. This article does not challenge these scientists. But do scientists generally agree that evolution is a fact? Some scientists and philosophers of science maintain that a very well-supported theory deserves to be called a fact. Others maintain that a theory never becomes a fact even if it is strongly supported. This essay intends to defend the latter use of the words fact and theory in scientific literature. This defense will involve a stipulated definition of the terms. Nevertheless, much of the literature traced in this article also reflects stipulated definitions, because the terms remain vague or fuzzy without such stipulations. While this may appear merely a verbal quibble, a clear distinction between fact and theory has significant implications for science education and scientific dialogue generally.
Charles Darwin on ‘False Facts’
There is also the question of the possibilities of “false facts,” a locution used by Charles Darwin in his Descent of Man (1871, 385). What Darwin surely meant when using the phrase “false facts” was that there are some assertions that are falsely believed to be factual. Because the conclusions or claims of science are always open to revision or falsification, such beliefs would not be unusual. However, no dictionary definition of fact would allow for the existence of “false facts.”
Evolution and Darwinism: A Distinction
The fact-theory distinction is conspicuous when dealing with evolution. Is evolution a fact or a theory? Or is it both a fact and a theory? The use of fact and theory in much public conversation reflects confusion about the two words. Evolution is often taken to mean Darwin’s theory of descent and modification by natural selection. However, in the biological sciences there is a distinction between evolution and a theory that seeks to explain the mechanisms of evolution. In these biological sciences, evolution is understood to mean the theory that organisms have descended with modifications from common ancestors. Evolution, in this sense, is affirmed by most biological scientists. The central question still pursued is the mechanism by which evolution occurs. This would involve a theory about evolution, such as Darwin’s theory of descent by natural selection.
For clarity, this essay will take evolution to mean “the theory that living creatures today have descended, with modifications, from earlier life forms.” Darwinism will function as a name for a theory that seeks to explain the mechanism of evolution by way of natural selection. The use of Darwinism as a means of clarifying an important distinction does not imply anything about the status of that theory. At this point, I will refrain from asserting that evolution is a fact as well as a theory. Darwinism, however, seems to belong clearly in the realm of theory—not fact. Darwinism is, nevertheless, a very strongly supported theory.
View I: Evolution as a ‘Fact’
Several scientists and philosophers of science have maintained that evolution is a fact. Douglas Futuyma writes “the statement that organisms have descended with modifications from common ancestors—the historical reality of evolution—is not a theory. It is a fact … 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.” Note that Futuyma’s assertions include a stipulated definition of fact.
Stephen Jay Gould asserts, “[E]volution 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.” He then writes, “In science ‘fact’ can only mean ‘confirmed to such a degree that it would be perverse to withhold provisional consent.’” Gould’s distinction between fact and theory is widely held in the scientific literature. Note that he also stipulates a definition of fact. While this definition is widely accepted, other scientists and philosophers of science do mean something else by the word fact. It does not “only mean” what Gould claims that it means. Furthermore, Gould’s claim that evolution is a theory and also a fact appears to be inconsistent with his claim that “facts and theories are different things.” If facts and theories are “different things,” how can evolution be both a theory and a fact? Perhaps he holds that a well-supported theory can be seen as a subset of facts and yet maintain its theory identity. Other biologists, such as Richard Lenski and Richard Dawkins, tend to agree with Futuyma and Gould by viewing evolution as a fact.
What Constitutes ‘Facthood’?
What, then, do the above scientists and philosophers mean by the word fact when they assert that evolution is a fact or has attained facthood? The above scientists would probably agree with the stipulated definition of fact as a proposition that has so much evidence in its favor that no reasonable and unbiased person could deny it. Evidently, then, as a hypothesis gains more and more scientific/empirical evidence in its favor, it can attain the status of fact.
These writers all agree that evolution once had the status of a hypothesis or theory before it gained the status of facthood. This appears to be an accurate claim. Evolution was once only a hypothesis or a theory when it was proposed as a way of explaining possible connections between or among direct observations. These would include observations regarding fossils that have certain resemblances to current life forms. However, the claim that current species were descendants from the creatures reflected in the ancient fossils could not have resulted only from a direct observation of such similarities. The observation O that fossil F has certain resemblances to a present life form L does not directly imply that L descended from F. Such an evolutionary claim would constitute a theory imposed upon those observational facts. That claim would have the status of a hypothesis that sought to explain the resemblances by way of an evolutionary link. So, also, the resemblance between chimpanzees and modern human beings is a direct observation (as, also, is the close DNA resemblance), but the claim that these two species shared ancient ancestors would not be a direct observation (fact) but a hypothesis posed to explain the resemblances. In short, evolution was never the result of direct observation only. Evolution was posited to explain resemblances noted by direct observation. For some scientists, evolution gained the status of fact when the accumulated evidence became so strong that no rational and unbiased mind could deny its truth. For those scientists, it then gained the status of facthood.
View II: No Theory Attains Facthood
Given this general agreement about the “facthood” of evolution by several scientists and philosophers, statements from an October 17, 2008, article from the National Center for Science Education (NCSE) are surprising. The article lists several misconceptions, which include: “Theories become facts when they are well supported and/or proven.” Later in that essay: “In science, theories never become facts. Rather, theories explain facts.” The article would no doubt grant that there are theories that are very strongly confirmed—the theory, for instance, that our solar system is heliocentric, not geocentric. Yet NCSE would maintain that these highly confirmed theories do not attain the status of fact. They hold that the task of a theory is to explain facts. However well it may be confirmed, a theory never becomes a fact.
This strict distinction between fact and theory is reflected in the chapter on the scientific method in Irving Copi’s widely used textbook Introduction to Logic. It is interesting to note that Samir Okasha, in his Philosophy of Science: A Very Short Introduction, never uses the word fact in conjunction with either evolution or Darwinism. He does not directly deny the status of facthood to either theory; he just never discusses that question.
NCSE on Fact
What, then, might the NCSE mean by fact? Roughly, the organization might assert that a fact is something that is directly or indirectly presented to our senses—most often, our sight. More technically, a fact is empirical data that is objectively verified through observation. This is what Gould apparently means when he writes that “facts are the world’s data.” It is a fact that when I dropped the pencil, it fell to the floor. It is a fact that when I threw the ball into the air, it fell to the ground. (The apple fell down from the tree.) When these facts are repeatedly observed, an explanation of those facts by way of a theory seems to be required. Those facts are now generally explained by Newton’s theory (Law?) of gravity.
The Meaning of Theory
While scientists may disagree about the definition of fact, there is general agreement about the meaning of theory. A theory is a statement of some general principle that explains the causes of something observed. Examples of such observations include:
1) In biological sciences, very old fossils that resemble the bone structure of modern humans are found in Africa. (The age of the fossils is determined by other theories.)
2) The physical structure of chimpanzees closely resembles that of human beings.
3) The DNA of chimpanzees is very similar to that of human beings.
These facts (observations) are explained by the theory of evolution. For NCSE, evolution is and must remain a theory because it cannot be directly or indirectly observed. Theories are unobservables. Facts are obtained by way of observations, and these facts are explained by theories.
Facts Can Be Theory-Laden
Some would properly point out that observations (pencils, balls, or apples falling) are often rich with prior knowledge and theoretical content. Facts are often theory-laden, which may suggest that there is no clear line between facts and theories. Yet, while facts may be theory-laden, such richly endowed observations can still be considered facts—observed phenomena—to be explained. A fact can be theory-laden and still remain a fact to be explained.
A Theory Is More Than a Collection of Facts
Furthermore, a theory is not to be understood as an accumulation of various facts. A cluster of observations (facts) does not a theory make. A theory materializes when someone seeks to give some sort of explanation regarding those facts. This point was made by a scientist who declared that there are two kinds of science: physics and stamp collecting. (The declaration was made, of course, by a physicist.) While taxonomy is an important field in the biological sciences, it is akin to “stamp collecting.” While the theories of evolution and Darwinism may not be directly akin to physics, they clearly move beyond just collecting and organizing data by attempting to explain the data.
Stipulated Meaning of Fact
It seems clear that any attempt to resolve the conflicting views regarding the use of the words fact and theory in scientific literature would involve stipulating meanings for the two terms to keep them distinctly different. But this need not be a problem because, as we have seen, that stipulation is apparent in the writings of Futuyma and Gould. This essay seeks to defend the position taken by the NCSE. For pedagogical purposes and for general use in scientific literature, a clear distinction should be made between facts and theories. While NCSE’s general view of the matter seems correct, it may go too far to assert that it is a misconception to maintain that a theory becomes a fact when it is well supported, because the conflicting views involve stipulated meanings for fact. Stipulated definitions are employed for clarity but are neither right nor wrong. With NCSE, I will support the view that theories remain theories, however well supported. The function of a theory is to explain facts, and that remains its function—however well supported it may be. Students in science should not be confused by the claim that a theory can evolve into a fact or that some theories are also facts. Keep the distinction clean. Theories remain theories. And theories explain facts. My argument will appear to be a “victory by definition.” Nevertheless, I will assert that the victory has some significant advantages.
A widely accepted definition in scientific literature for fact is some directly or indirectly observed phenomena. The factual status of some proposition P is more firmly established if it is supported by several such observations. It is a fact that every time I let go of my pencil, it fell to the floor. To be sure, factual claims are not always accurate. I may falsely believe X is a fact. In this sense, facts are akin to theories. Theories may also turn out to be false in the sense that they do not adequately explain the observed facts. Darwin’s observation about “false facts” highlights the possibility that some claim X may be falsely believed to be a fact. But observed phenomena are the facts that are to be explained by theories. Curiously, this is true even if the facts to be explained turn out to be falsely believed to be facts. For instance, some scientists once believed that planetary motion was perfectly circular and then proceeded to explain that “fact” with an appropriate theory. It could be argued that the theory came first—celestial motion is perfect, and only purely circular motion can be perfect—therefore [fact claim] planets move in perfectly circular motion. Factual claims may, indeed, be theory-laden.
Why Grant Facthood to Theories?
What might be the advantages in defining fact in such a way that a well supported theory can attain facthood? It is a commonly held view regarding such theories, as claimed by Futuyma, Gould, and others. Most persons with some education would consider the heliocentric theory of our solar system a fact. In that sense, it has become almost an intuitive position. But even though such a claim is commonly held, there may be advantages in a differing position.
Some worry that referring to evolution as a theory weakens its status in common parlance. Some worry that if evolution is a “theory,” biblical fundamentalists may gain an advantage by allowing them to claim that evolution is “only a theory.” Such fundamentalists need only to be reminded that the heliocentric view of our universe is also a theory. And the germ theory of disease is also a theory. We live and die by theories. Furthermore, if scientists maintain against such fundamentalists that evolution is a fact, not just a theory, the fundamentalist can just deny that it is a fact. Fundamentalists should not be allowed to control how terms are used in scientific literature.
Why Theories Ought Not Attain Facthood
If theories can gain the status of facthood upon sufficient evidence, how are we to decide when evidence is “sufficient”? Sufficiency surely involves a strong element of subjectivity, even among scientists. There seems to be no way of quantifying “sufficiency.” It remains both fuzzy and subjective.
Does a theory somehow attain more status when it is declared a fact? To declare that a theory has moved on to be a fact seems to diminish the significance of theory as over fact. Give theories their own significance by evaluating them in terms of the amount of evidence in support of the theory. A solid theory need not be “elevated” to facthood to heighten its credibility or status. To do so is to denigrate the significance of the concept of theory. Theories constitute the power of science. One might claim that theories are more significant than observational facts.
In Support of NCSE’S Position
What, then, are the advantages of embracing NCSE’s position? What good reasons might there be for keeping a clear line between facts and theories and thus maintaining that a theory never becomes a fact no matter how much support it might gain?
First, there is no particular advantage in asserting that a well-supported theory can be considered a fact. While that is not an uncommon assertion, the scientific literature can get along very nicely by rejecting that view and maintaining that theories always remain theories and never become facts. Nothing is lost in holding that position, and it is accepted by many scientists and philosophers of science.
Furthermore, the scientific method is clarified by keeping a clear distinction between fact and theory. Scientists begin with certain observations (facts) and then seek to construct some theory that can help to explain those facts. (Newton: The apple fell down, not up; his theory of gravity explains why this occurred.) Nonscientists will better understand the scientific method if they recognize the clear distinction between a fact and a theory. Growing a theory to the status of fact tends to confuse scientific processes.
There is also the puzzle that appears when a theory gains facthood. If some theory T gains the status of fact, does that fact, then, require some theory to explain it? To be sure. However, perhaps not all facts call for some explanatory theory.
Some Conclusions
I will not claim that serious thinkers are wrong when they maintain that a well-confirmed theory should gain the status of fact. Stipulated definitions are involved on both sides of the issue, and stipulations can hardly claim absolute truth.
However, I do want to close by asserting that keeping a clear distinction between facts and theories does not hinder the scientific enterprise. I do want to argue that keeping the distinction clear can be of help by clarifying the scientific method for both students of science and the general public.