Depending on who makes it, the claim that there is no evidence for evolution is either a lie or a gross mistake. The true issue is not whether the evidence exists. The issue is whether the evidence is sufficient to justify belief in the common ancestry of life on earth.
The genealogical relatedness of all modern organisms is considered a fact by nearly all biologists and the vast majority of scientists in other specialties. It is considered a fact by those scientists that humans share a common ancestry with the other organisms inhabiting this world. There is much debate over details of how the descent and diversification occurred, under what constraints the process operated, and what forces might have affected the rate at which it occurred. The evidence is not yet sufficient to answer many of those questions about details. For some questions the evidence will likely never be sufficient.
But those questions have to do with how it happened. That it did happen is regarded as a settled fact by nearly all scientists and by most scientifically literate laypeople.
This consensus is not itself proof of anything. Nothing is so just because a lot of people say it is so, even if a lot of those people are experts.
But neither does "The experts could be wrong" imply "The experts are wrong." A claim of reasonable doubt must come with reasons. Any theory can be wrong. Even an assertion of fact can be wrong. But that alone does not mean that any particular assertion of fact or theory is wrong.
To establish reasonable doubt, the dissenter must show by cogent argumentation that the facts leading the scientific community to accept common descent are illusory, or that the logic connecting the facts to the consensus conclusion is fallacious. Creationists have never done this. The facts are as stated and creationists have never proven the contrary. The scientists' logic is valid, and creationists have never proven the contrary.
The notion of reasonable doubt is very relevant here. It is appropriate to ask, after examining all the facts having some plausible relevance to an understanding of life's history, whether it is reasonable to think that the community of scientists have made a mistake as monumental as creationists claim they have.
Of course the scientists could be wrong. They are human, and there are no infallible humans. But by the same reasoning, the creationists could be wrong, too, and so they gain nothing by raising the possibility of human error.
What the impartial observer may do is note that either the scientific community or the apologetic community has made a significant error, and then ask himself or herself: For which of the two following propositions does the evidence allow the more reasonable doubt?
Responses to creationist objections
(This page last updated on August 6, 2010.)