by Richard Dawkins
I once tried to persuade an American atheist conference that the slogan, “In God We Trust”, on banknotes was a cosmetic trivium. We should stop bellyaching about it and concentrate our fire on more substantive issues such as the tax free status of churches. I was kicked around the room by the admirable Edwin Kagin, unfortunately now dead. It really matters, he said, not only because it’s unconstitutional but because many Americans, ignorant of history (the phrase was added as late as 1957) actually point to “In God We Trust” as evidence that America was founded in Christianity.
Our habit of referring to the “theory” of evolution is similarly used to mislead. Huge numbers of people are bamboozled by the phrase “Only a Theory.” This essay is designed to remove confusion by abandoning the word theory altogether, when talking to creationists.
Today the dominant reply to the creationist “only a theory” bleat is to explain that the meaning of “theory” in science is different from everyday usage, which is synonymous with “hypothesis”. In The Greatest Show on Earth I quoted two definitions from the Oxford English Dictionary:
Theory, Sense 1: A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment, and is propounded or accepted as accounting for the known facts; a statement of what are held to be the general laws, principles, or causes of something known or observed.
Theory, Sense 2: A hypothesis proposed as an explanation; hence, a mere hypothesis, speculation, conjecture; an idea or set of ideas about something; an individual view or notion.
The party line among scientists arguing for evolution is to promote Sense 1, and I have followed it until today. But now I want to depart from the party line. I now think that trying to clear up this terminological point about the meaning of “theory” is a losing battle. We should stop using “theory” altogether for the case of evolution and insist, instead, that evolution is a fact.
Philosophers, I am aware, can be relied upon to cloud even the word “fact”. A fact can never be more than a hypothesis on probation, a hypothesis that has so far withstood all attempts to falsify it. The more strenuous those attempts, the closer we come to endowing the accolade of fact. I am fond of Stephen Jay Gould’s way of putting it. “In science, ‘fact’ can only mean ‘confirmed to such a degree that it would be perverse to withhold provisional assent. I suppose that apples might start to rise tomorrow, but the possibility does not merit equal time in physics classrooms.” Courts of law, newspapers, and all of us in everyday life use the word “fact” in a way that few have difficulty in understanding. It is a fact that New Zealand is in the Southern Hemisphere (Barack Obama is the US President, it is now raining in Oxford, grass is green etc). It is this everyday usage of “fact” that we should be concerned with when we advocate evolution to lay audiences. We are failing to get across “Theory, Sense 1”. Let’s dump it and talk frankly of evolution as a fact, from which it would be perverse to hold assent.
Our failure to get across Sense 1 is partly blamed on an everyday tendency to leap straight to Sense 2: theory as tentative “mere” hypothesis. But we must admit that scientists themselves use “theory” in a way that might strike the poor layman as confusingly inconsistent. “String Theory” has elements of Sense 1. It is indeed a “scheme or system of ideas or statements” but it is very far from being “confirmed or established by observation or experiment”. It isn’t even clear how anyone might set about testing it by observation or experiment. Yet it is always called String Theory, not String Hypothesis. “Theory of games” is not something that can be “confirmed or established”: it is, rather, a technique of reasoning which, originating in the mathematical study of games, has proved useful in a variety of different fields. Marxist Theory is definitely “a scheme or system of ideas, held as an explanation or account” of human economics and sociology (and as a normative recipe for politics) but again you have to ask “held by whom?”
Charles Darwin made frequent reference to his “theory”, and in his time it was a theory in Sense 2: a hypothesis whose supporting evidence at the time persuaded some scientists but by no means all. In the succeeding century and a half it has moved from Sense 2 to Sense 1, indicating that there is a continuum, in this case historically traceable, between Sense 2 and Sense 1. Nowadays no knowledgeable scientist has any doubt of the fact of evolution: it is an indisputable fact that we share common ancestors with our cousin gorilla, and with our more distant cousin kangaroo.
Some scientists speak of the fact of evolution, as distinct from Darwin’s hypothesis of its mechanism (natural selection). They would relegate natural selection, but not evolution itself, to a Sense 2 theory. Others feel that natural selection is so well established as the only known mechanism for producing adaptive evolution that its historical progression from Sense 2 to Sense 1 is now almost as complete as that of evolution itself.
In our tussles with creationists it is evolution itself rather than natural selection that bears the brunt of their attacks. So we can set aside the status of natural selection and concentrate on the fact of evolution as something so firmly established by evidence that to deny it would be perverse. It is a fact, beyond all reasonable dispute, that if you trace your ancestry and your dog’s ancestry backwards you’ll eventually hit a common ancestor. It is a fact, beyond reasonable dispute, that when you eat fish and chips you are eating distant cousin fish and even more distant cousin potato.
Confusion of a different kind is introduced by those who agree to abandon “theory of evolution” but try to replace it by “law of evolution.” It is far from clear that evolution is a law in the sense of Newton’s Laws or Kepler’s Laws or Boyle’s Law or Snell’s Law. These are mathematical relationships, generalisations about the real world that are found to hold true when measurements are made. Evolution is not a law in that sense (although particular generalisations such as Dollo’s Law and Cope’s Law have been somewhat dubiously introduced into the corpus of Darwinian theory). Moreover, “Law of Evolution” conjures up unfortunate associations with grandiose overgeneralisations linking biological evolution, cultural evolution, linguistic evolution, economic evolution and evolution of the universe. So please, don’t make matters worse by turning evolution into a law.
Let’s simply give up on trying to explain the special scientific meaning of “theory”. It is begging to be misunderstood by laymen eager to misunderstand, and even scientists are not consistent in their usage. The ordinary language meaning of “fact” (it is a fact that New Zealand is in the Southern Hemisphere) and the scientific meaning (the evidence for evolution is so strong that to withhold assent would be perverse) are close enough to obviate confusion in the mind of all but the most doggedly pedantic philosopher. By all means postpone for another day the question of whether natural selection is also a fact. For now, when arguing with creationists, let’s sweep confusion aside by means of a strategic retreat from the word “theory”. Let’s sacrifice a pawn for strategic advantage and hammer home a clear message that everyone can understand, and which is undeniably true in the everyday sense. Evolution is a fact.
Evolution is a fact.