There is an old and tiresome Creationist claim out there which says that theories of evolution are not scientific because they can't be repeated or tested. Such a claim states that since nobody was around to directly observe the transition from amphibians to reptiles, for instance, that to theorize such a scenario is not scientific.
A thought struck me as a good way to explain why such a claim is false. Before I do, however, I'd like to point out that much of the groundwork for evolutionary theories has indeed been directly observed in recorded human history. Random mutations do occur and are selected for when beneficial to organisms in their particular environment. Transitional fossils occur in the geologic column in a manner consistent with the predictions that evolutionary theories make. You can learn more by clicking on the Talk.origins link in the FYI section of this blog. Pay special attention to the '29+ Evidences of Macroevolution.'
I'd like to use the example of forensic science to make the main point here. My intent is to demonstrate why both forensics and biological evolution are valid scientific approaches to knowledge and truth - and to tag on the conclusion that 'God did it' cannot meaningfully be used in the realm of scientific inquiry.
For one thing, forensics provides a great example of how the scientific method works.
1. You observe a phenomenon: A person has died.
2. You formulate and propose a hypothesis for how that series of events came about.
3. You collect data and test the hypothesis against those data.
4. You analyze the results, form conclusions, and either reject the hypothesis or modify it to fit the evidence.
5. If the theory holds up, you run it by a group of people who can view your findings and conclusions, declaring them either valid or invalid.
None of this involves *being there* to directly observe the events. None of the events need to be repeatable. Yet... this is still science. In forensic studies, people collect evidence regarding past events, and they construct a theory to explain the evidence. The same is true of evolutionary theories.
Several important criteria for scientific theories make it clear that 'God did it' cannot be a valid explanation in the realm of science. Most relevant are the ideas that scientific theories must be able to explain past and to predict future phenomena, and that useful scientific theories must be falsifiable.
If we try applying 'God did it' to our murder case, it's clear how useless the theory is. What sort of things would we predict if God did murder the victim? What sort of findings would falsify the theory?
Take a step back for a moment. Imagine instead of 'God did it,' we hypothesize 'Mother Theresa did it.' Well, if she was responsible for the murder, what would we predict to find? We might predict that she had a motive to murder, was in the vicinity when the murder took place, and perhaps left traces of her presence - fingerprints, blood, hair, etc. To falsify the theory, we could prove that Mother Theresa is dead. We could prove that she wasn't in the vicinity, and that she left no traces at the crime scene. More potently, we could prove that another person was in the vicinity and left traces of his or her presence.
The 'God did it' theory is powerless to make predictions. It could include absolutely anything. There is nothing we can do to empirically test the idea, and no possible discoveries or evidences are able to falsify the theory. For those two reasons alone, 'God did it' is a worthless hypothesis to make in the realm of scientific inquiry - whether or not it is true.