Is there a reason Shadow looks a lot like Sonic?

When he was created, why did Gerald make Shadow a TALKING hedgehog, that can walk on 2 feet? Unless he somehow knew about animals like that from Sonic's world or something. Neither the series or the game ever explained why he made Shadow that way. I guess it's just another 1 of those plot wholes that will remain unexplained.

Shadow: I am Shadow...Shadow the Hedgehog!