Similarities between species are evidence for evolution, but the evidence is decidedly mixed. While there are similarities that support the evolution expectation, there are others that contradict the pattern. But erroneous similarities are particularly persuasive for evolutionists.
For example broken genes, referred to as pseudogenes, are sometimes found to be disabled by identical mutations in cousin species. As evolutionist Jerry Coyne concludes in his book Why Evolution is True, “Only evolution and common ancestry can explain these facts.” 
That of course is the sort of non scientific, metaphysical, IF-AND-ONLY-IF claim which is fundamental to evolution. Coyne summarizes this important finding:
But if you believe that primates and guinea pigs were specially created, these facts don't make sense. Why would a creator put a pathway for making vitamin C in all these species, and then inactivate it? Wouldn’t it be easier simply to omit the whole pathway from the beginning? Why would the same inactivating mutation be present in all primates, and a different one in guinea pigs? Why would the sequences of the dead gene exactly mirror the pattern of resemblance predicted from the known ancestry of these species? And why do humans have thousands of pseudogenes in the first place? 
Should we laugh or cry? The evolution genre is loaded with such trash posing as science, yet I am still struck by the astonishing banality of evolutionary thought.
Of course Coyne omits the scientific details. He omits the findings of non randomness of mutations. And he omits the examples of pseudogenes that don’t fit the pattern, which require even evolutionists to admit to convergent mutations. He omits the fact that evolution fails to explain how the protein synthesis machine, including the genes, arose in the first place.
But can these omissions be at all serious when Coyne and the evolutionists know evolution must be true? After all, they know what a creator would and would not do, and obviously said creator would not have created these pseudogene patterns. Indeed, he wouldn’t have created pseudogenes at all. The evolutionist’s anti intellectualism is exceeded only by his certainty.
The fact that evolution struggles with the evidence is of little consequence—it is true by virtue of creation being false. So what if pseudogenes do not always cooperate. Elliot Sober calls this Darwin’s Principle.
This naïve and facile dorm room argument reveals the astonishing level of anti intellectualism at the heart of evolutionary thought. It is the junk religion behind the junk science. Religion drives science, and it matters.