The real answer (I LOOKED IT UP... YEAH INTERNET
) Is that Gravity is thought (warning: unproven science ahead) to be caused by Graviton particles that have yet to be discovered. We are hoping to learn something from the Higgs Boson particles relevant to gravitons (LHC).
However, until we are able to discover these particles, this is just theory, and we don't actually know what causes gravity.
Also, we believe that the Higgs Boson particles are what gives matter mass. And it is also believed that the Higgs Boson and the Graviton are related in some manner (although it is unclear how).
This theoretical relationship is probably what lead to the belief that if Gravity existed, then it could create Higgs Boson particles.
That being said, until we find gravitons this is all theoretical conjecture. We believe they exist, but we have no proof that they actually do. Therefore, we have no way of knowing whether gravity existed prior to the Big Bang.