What would falsify Evolution?
We all know that a characteristic of science is that it must be falsifiable. Scientific theories cannot be proved – only disproved.
Evolution is based on three principles: variation, heritability and selection; if any of these were shown to be flawed then the theory would be untenable. Consequently any of the following would destroy the theory:
- If it could be proven that mutations did not occur.
- If it could be proven that although mutations did occur they were not passed down through the generations.
- If it could be shown that selection or environmental pressure did not favor the reproductive success of better adapted individuals.
Darwin made the case a little differently when he said, "If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down."
What would falsify common descent?
Common descent could easily be disproved (without even seriously challenging the theory of evolution) if we discovered a form of life that was not related to all the life we know - most simply, by finding life that does not use the nucleic acids (DNA and RNA) for information storage and retrieval.
Also, if we were ever to discover life elsewhere in the universe, the odds lean towards it not having a common ancestor with life on earth. See Alien.
What about a Precambrian rabbit?
First of all it must be remembered that the fossil record is supporting evidence for evolution. If the fossil record simply did not exist, that would make no difference to the validity of the theory of evolution.
The simple truth is that a single strange fossil would probably not make much difference. The evidence in the fossil record which supports evolution is so overwhelming that a single fossil would be regarded as curious certainly; but compared to the mountain of evidence in favor of evolution it would probably be regarded as an anomaly while more data was awaited.
However, the existence of entire groups of anomalous fossils would be a different thing. An effort would initially be made to fit the new data into the existing framework. This is not cheating but simply the way that science works.
For instance, If problems were found in general relativity scientists would first see if the theory could be adapted to include the new data, if it could not then a new hypothesis would have to be formed which would go through the normal scientific testing process. The same thing would happen to our descriptions of the fossil record.
What would happen if the entire fossil record were shown to have been faked, or if a vast number of fossils were found which could not be fit into the current schemes? In this rather contrived and hugely hypothetical case, there would be a contradiction of evidence which would have to be resolved. The scientific method would have to be used to resolve it.