In the NBC television series Heroes, the superhuman abilities of the "Evolved Humans" (colloquially known as "EVOs") are the result a special gene complex involving two genes, each of which has two forms, or alleles. To be an EVO, a person must have at least one of each of the dominant alleles. The special gene complex creates a special protein that interacts with stress hormones, behavior-related neurotransmitters, immune system messengers, and other biochemical characteristics to produce chemical signals that modify the expression of susceptible genes. The special protein is a type of "genetic enhancer."
For example, Claire Bennet's rapid cellular regeneration could be explained by the special protein having magnified the expressions of the genes responsible for normal cellular regeneration to the point that her body is able to spontaneously regenerate cells at an increased rate, completely healing physical injuries in a matter of seconds and giving Claire an incredible tolerance for pain. Similar explanations extend to all EVOs. While the information in their genes that dictates biological characteristics has remained the same, the set of actual physical traits exhibited has been altered and enhanced through the special protein modifying genetic expression.
Because the specifics of the biochemical characteristics that interact with the special protein are dependent upon a person's environment, individual genetic structure, and even emotional/psychological state, the specific chemical signals produced are different in every EVO. As a result, the expressions of what specific susceptible genes are altered and enhanced and how they are altered and enhanced are different in every EVO. That's the reason every individual EVO has a different superhuman ability.