Obviously, they can't. All they can do is ignore, denigrate, or sidestep those facts and pieces of evidence that are in conflict with their mythical beliefs, and resort to false, deceitful, nonsensical, baseless, fraudulent, dishonest, and unprincipled arguments in their attempts to prove that there is no evidence for evolution.
That is well exemplified by @no1home2day, who has repeatedly used those types of arguments even though I have repeatedly refuted everything he has said.
Well, if he won't accept my arguments, perhaps he will rethink things after seeing what CREATIONIST Todd C. Wood, a Research/Associate Professor of Science at the Christian-based Bryon College, says about evolution. It is quite relevant in regard to @no1home2day and all of the other creationists here on Yahoo!Answers who say there is no evidence for evolution and that it is a failed theory.
Here is what Professor Wood says (and @no1home2day should pay particular attention to the second paragraph):
"Evolution is not a theory in crisis. It is not teetering on the verge of collapse. It has not failed as a scientific explanation. There is evidence for evolution, gobs and gobs of it. It is not just speculation or a faith choice or an assumption or a religion. It is a productive framework for lots of biological research, and it has amazing explanatory power. There is no conspiracy to hide the truth about the failure of evolution. There has really been no failure of evolution as a scientific theory. It works, and it works well.
"I say these things not because I'm crazy or because I've "converted" to evolution. I say these things because they are true. I'm motivated this morning by reading yet another clueless, well-meaning person pompously declaring that evolution is a failure. People who say that are either unacquainted with the inner workings of science or unacquainted with the evidence for evolution. (Technically, they could also be deluded or lying, but that seems rather uncharitable to say. Oops.)
"Creationist students, listen to me very carefully: There is evidence for evolution, and evolution is an extremely successful scientific theory."
But, of course, since he is a creationist, he then he goes on to say:
"That doesn't make it ultimately true, and it doesn't mean that there could not possibly be viable alternatives. It is my own faith choice to reject evolution, because I believe the Bible reveals true information about the history of the earth that is fundamentally incompatible with evolution."
http://toddcwood.blogspot.com/2009/09/truth-about-evolution.html
So there you have it. The Bible is the word of god, period, and the facts be damned.
But I would hope that, after reading what Professor Wood said about the evidence for evolution, @no1home2day would stop "pompously" using his false, deceitful, nonsensical, baseless, fraudulent, dishonest, and unprincipled arguments in his attempt to prove that there is no evidence for evolution and that it is a failure as a scientific theory.
But, quite frankly, I doubt he will.
Added:
I won't even go into @voyc4rmwldrns's inarticulate, nonsensical rantings. He should also understand that he has a full keyboard to make use of and does not need to make his nonsense even more incomprehensible by using text shortcuts.
Added:
Sigh!
The creationists here keep repeating the same false, nonsensical tripe they find on lying creationist web sites. For example, some have referred to the Cambrian explosion as evidence against evolution. That is crap!
The fossils in the Cambrian strata, in fact, fit in quite well with the evolutionary process. The Cambrian explosion actually lasted several tens of millions of years, and in Cambrian strata you will find the initial appearance of most of the phyla, but they will be only very primitive species--none of which exist today--belonging to those phyla. You will not find one single amphibian, reptile, dinosaur, bird, mammal, or teleost fish. It was during the Cambrian that hard body structures first came into existence; that is why there are numerous fossils of Cambrian organisms in contrast to fossils of the soft-bodied precursors, but, contrary to the lies you find in creationist web sites, fossils of the precursors have been found.
http://en.wikipedia.org/wiki/Cambrian_explosion
It is also a creationist lie that no transitional fossils have been found.
http://en.wikipedia.org/wiki/List_of_transitional_fossils
http://en.wikipedia.org/wiki/Transitional_fossils
http://www.holysmoke.org/tran-icr.htm
http://blogs.myspace.com/index.cfm?fuseaction=blog.view&friendId=229081369&blogId=371847244
http://en.wikipedia.org/wiki/Feathered_dinosaurs
http://news.bbc.co.uk/2/hi/science/nature/1081677.stm
http://dinosaurs.about.com/od/thedinobirdconnection/a/dinobirds.htm
http://dinosaurs.about.com/od/thedinobirdconnection/a/dinobirds_2.htm
And this series in particular.
http://www.talkorigins.org/faqs/comdesc/hominids.html
As for the origin of life, all that is needed for the path to life to start is a self-replicating molecule. It doesn't even need to code for anything, and such molecules have even been created in lab by spontaneous processes.
http://www.wired.com/wiredscience/2009/05/ribonucleotides
Here is a quote from that site:
"[T]hough researchers have been able to show how RNA’s component molecules, called ribonucleotides, could assemble into RNA, their many attempts to synthesize these ribonucleotides have failed. No matter how they combined the ingredients — a sugar, a phosphate, and one of four different nitrogenous molecules, or nucleobases — ribonucleotides just wouldn’t form."
But now the ribonucleotides have been spontaneously formed in the lab--it was just a matter of finding the correct precursor chemicals. And this is a quote from the scientist involved, again from the site.
“Ribonucleotides are simply an expression of the fundamental principles of organic chemistry,” said Sutherland. “They’re doing it unwittingly. The instructions for them to do it are inherent in the structure of the precursor materials. And if they can self-assemble so easily, perhaps they shouldn’t be viewed as complicated.”
So scientists have shown that ribonucleotides can spontaneously form from precursor chemicals, and also that RNA can spontaneously form from ribonucleotides.
Given what can take place in a lab, what can take place in the whole earth and over millions of years is not hard to conceive. Here are some sites that provide evidence of how life began.
http://www.sciencedaily.com/releases/2002/12/021204080856.htm
http://www.gla.ac.uk/projects/originoflife/html/2001/pdf_files/Martin_&_Russell.pdf
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1693098&blobtype=pdf