The initial movement was led by physicians, but also included politicians and feminists. Among physicians, advances in medical knowledge played a significant role in influencing anti-abortion opinion. Quickening, which had previously been thought to be the point at which the soul entered a human was discovered to be a relatively unimportant step in fetal development, caused many medical professionals to rethink their positions on early term abortions.[17] Ideologically, the Hippocratic Oath and the medical mentality of that age to defend the value of human life as an absolute also played a significant role in molding opinions about abortion.[17]