Terry Tao has given a clear argument for the case that it is indeed not necessary to be a genius to do mathematics:

“The answer is an emphatic NO. In order to make good and useful contributions to mathematics, one does need to work hard, learn one’s field well, learn other fields and tools, ask questions, talk to other mathematicians, and think about the “big picture”. And yes, a reasonable amount of intelligence, patience, and maturity is also required. But one does not need some sort of magic “genius gene” that spontaneously generates ex nihilo deep insights, unexpected solutions to problems, or other supernatural abilities.”

And as to sufficiency, Randy Rainbow gives a compelling argument that being a very stable genius is not sufficient to ensure one has the reasonable amount of *intelligence*, *patience,* and *maturity* that Terry Tao sees as a requisite to be good at mathematics (or pretty much anything else, in fact):