The research currently shows that a) there are specific genes associated with stuttering, b) there are consistently underlying structural differences in the brains of people who stutter from people who don’t. Sure our speech patterns are influenced by our environment, but there is 100% a genetic and neuro-physiological component. I hear you’re reflecting on your experience, but there are tons of scientists working on answering these very questions scientifically - this is a great collection of information on that research https://www.nidcd.nih.gov/health/stuttering#causes