What do scientists mean when they use the word
You often hear non-scientific people say, "The theory of
evolution is only a theory." And they
imply that the word 'theory' means 'best guess' or
But what do scientists actually mean by a 'scientific theory'.
Is it different from the public's understanding of the word. Can
you prove a theory?
Dictionaries are very helpful in these discussions. I have
picked the following, highlighting what I think is
most helpful with your questions:
A well-substantiated explanation of some aspect
of the natural world; an organized system of accepted
knowledge that applies in a variety of circumstances to
explain a specific set of phenomena
a plausible or scientifically acceptable general
principle or body of principles offered to explain
a coherent group of general propositions used as
principles of explanation for a class of phenomena
The problem stems from the other uses of the word theory,
also present in the same dictionaries. What you see
above are those that, in the minds of scientists, would apply
to the theory of Evolution. It is a totally different status from
other uses of the word, some of them more akin to hypothesis,
conjecture or speculation. This prompts the formulation of
differential statements, such as the following
Theory, hypothesis are used in non-technical contexts to mean an
untested idea or opinion. A theory in technical use is a
more or less verified or established explanation accounting for
known facts or phenomena: the theory of
relativity. A hypothesis is a conjecture put forth as a
possible explanation of phenomena or relations, which serves as a
basis of argument or experimentation to reach the truth: This
idea is only a hypothesis.
Finally, when Pope John Paul II made his famous statement to the
effect of 'Evolution is more than just a hypothesis', he added
'there is more than one theory'. Both statements must be
acknowledged as correct, the second however with a qualification:
the diversity of scientific discourses on Evolution deal with
details, such as accepting or not Kimura's neutral theory, or
Eldredge & Gould's punctuated equilibria theory (I, for
one, accept both as very illuminating complements of the work
of Charles Darwin). The principles laid down by Charles Darwin,
complemented by the Genetics amendments made by Fisher, Wright and
Haldane in the early 20th century, are taken as the best
scientific explanation on the diversity of extant and fossil life.
Even when creationists and ignorant journalists construe the Flores
man and Ardi as evidence against the Evolution theory. Quite the
contrary, they serve as new examples of the original way of
explaining evolution set by Charles Darwin.
Not proof, but examples. A theory as defined above is an
explanation, not a fact, hence no proof required. But while you
cannot deny facts, you can deny theories. Saying that a theory is
verified (like in one of the quotes above) it means that it has not
been denied, actually.
This is why I choose to write 'best scientific
explanation'. The challenges of new facts are a constant test
on the theory, and scientists would be the first to acknowledge its
invalidity. Science cannot afford to be dogmatic.