[shubi]

Right, so why would God create them with a design deficiency?

This is evidence that evolution is correct and creationism isn't.

[DannyTN]

"Right, so why would God create them (chimps, guinea pigs) with a design deficiency (inability to synthesize vitamin C)? "

There is no reason to believe it's a design deficiency.

There are two possibilities:

1. They were designed that way for a reason that we have yet to discover, or
2. They were designed with the ability to synthesize vitamin C and due to the curse on the earth have lost that ability due to mutations.