Gday,
Thanks Copernicus
Here is my attempt to give a full picture of how 'theory' applies to evolution.
Two common uses of the word theory can be boiled down to :
1. explanation
2. speculation
A
speculation theory can be right or wrong.
An
explanation theory can also be right or wrong.
It is not always black and white - sometimes a theory can even have both meanings - by being a speculative explanation - such as the "Demonic Theory of Disease".
The Demonic Theory of Disease speculates that disease is explained by demons. This particular explanation (theory) for disease is completely speculative (there is no actual evidence for demons), and - it is a WRONG explanation.
But consider the more modern competing explanation for disease - the "Germ Theory of Disease". This particular explanation (theory) of disease is NOT speculation - it is based on observation. It's a fact.
The Demonic Theory (explanation) of Disease was speculation - and it was wrong. Demons were just a theory, and the theory turned out to be wrong.
The Germ Theory (explanation) of Disease started out as speculation e.g. when Lister hypothesized germs were causing sepsis. He was spectacularly right - his theory (speculation) was correct. Now we have direct evidence for germs and their cause of disease, and so the Germ Theory (explanation) for Disease is considered a fact.
Typically such speculation early in the scientific process is refered to as a 'hypothesis', sometimes a 'conjecture'. Then the hypothesis is tested with a experiments. Lister tested his hypothesis by performing surgery under a fine spray of anti-septic (1867.)
Such tests will support or disprove the hypothesis - but strictly speaking never 'prove'. After directly observing germs causing disease in practice, our evidence for germs is so solid it's a fact(*). When we refer to the Germ Theory of Disease no-one says "aha! so germs are still just a THEORY!"
(*) Strictly speaking all facts are provisional, but once something has vast overwhelmign evidence, it's just called a 'fact'.
Now - evolution.
Sure enough Darwin started by proposing a
speculative claim - a hypothesis, a conjecture.
Boiled down to the nubbin his hypothesis, his speculation, his conjecture was this :
Natural selection (descent with modification) explains the origin of all species on earth
So Darwin's theory (or explanation) was indeed
speculation in his time - it had not been fully supported by evidence, not accepted by science. (Of course the actual facts of nature were true before science understood them.)
So - Darwin's explanation of evolution was originally speculation.
But quite quickly the evidence to support Darwin's hypothesis began to accumulate. Not just that but prior observations and experiments were put into sharp relief by Darwin's hypothetical explanation.
It became clear that Darwin was right - very very clear and obvious. Eventually the evidence was so great than Darwin's explanation was no longer considered speculation - it was considered a fact.
So it is indeed true that Darwin's hypothetical explanation started as speculation - is now considered as a factual explanation - because the evidence is so strong.
His hypothesis was confirmed as correct. The evidence is SO solid, it is as strong a fact as anything in biology. His hypothesis became accepted as a fact.
Nonetheless it is still a formal scientific explanation, it can still be called a THEORY - an explanation. In the same way that gravity can be called a theory - actually TWO theories, so scientists often talk about Newton's Theory of gravity and Einstein's Theory of gravity.
Generally - biologists don't refer to the "Theory of Evolution" unless they want to emphasize the theoretical aspect - usually it's just refered to as "evolution". Same as physicists refer to "gravity" or "electricity".
But creationists sieze on this word "theory" and spin out on word games about "speculation".
Iasion