Next time some fundie tries to pull that "It's only a theory" bullshit on you tell them this:

Sometimes a theory is not just a theory

A recent entry in the ongoing discussion of evolution on this page (“A theory is just that until it is proven,” June 6) unfortunately illustrates two common misunderstandings: one, of the meaning of the word “theory” in a scientific context versus its common use in everyday speech, and the other regarding what constitutes scientific “proof.”

The scientific method requires that a hypothesis be tested by seeking to disprove it. If an experiment shows that a hypothesis is wrong, the hypothesis must be either rejected or updated to reflect the new findings. While, in common parlance, a “theory” is an untested idea awaiting verification, in a scientific context, a “theory” is a hypothesis that has been repeatedly tested and still survives. In this sense, a scientific theory is held to a higher standard of proof than, for example, a verdict in a court of law, which requires only proof beyond a reasonable doubt.

That evolution has occurred is patently clear from the fossil record, which documents the incremental changes leading to many of the organisms we see today. The “theory” that evolution has occurred by natural selection has survived 150 years of rigorous testing and remains one of our strongest and most useful scientific findings.

-- Mike Livstone, Ph.D.,
East Windsor

The writer is scientific curator at the Lewis-Sigler Institute for Integrative Genomics at Princeton University. He writes in his capacity as a private citizen.

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.