Elephants would not have to evolve, we have only 3 species and that would make 6 individuals.
Also, I could prove that most species are in fact not species at all since the differences are so small. I'll use some muddled logic about prokaryots not being a species until they share 80% of the same genetic information and thus I could prove that mice are not mice, but only unrecognizable moles!
Those darn biologists have been fibbing to us all this time.
I was also thinking that the lack of genetic diversity found in cheetahs could be easily explained by this ark thingy. It would support the idea that this species in particular would prove beyond a shadow of doubt that Earth is in fact only 6,000 years old. Yeah yeah, that's the ticket!
I'll even put in a chapter about how the genetic clock will show that the Earth will end in exactly 42 years from now. Can't figure an angle on this one yet.