Why does shadow look like sonic

One theory is that the "animals" of Sonic's Universe tend to look similar. One can look towards the Echidna race. They have features similar to Knuckles the Echidna which can be seen in various flashbacks in Sonic Adventure. Also, Shadow cannot be a clone of Sonic because Shadow was unsealed by Dr. Eggman 50 years later after the Space Colony Ark incident. Shadow can also be seen as a different race of hedgehog due to him having more fur and his signature markings.


I'm srry, I think I know the simple, correct answer: He is a hedgehog, as is Sonic (I honestly dont know how the people in the TV series and the games could confuse them, they must be stupid).
Side Note: Oh and btw, Shadow IS NOT a clone of Sonic. He was created at least 35 years before Sonic was made (subtract the 15 years he is supposed to be old).