What does it mean to be self-sustaining?
A system can be considered self-sustaining to the degree it can continue in a healthy state without external support.
A need to survive sustains every form of life on earth. Fear tends to drive survival, portraying perhaps a more sinister side to self-sustaining behavior – the need to do whatever it takes to continue. This need to continue is the essential core ingredient and motivation in evolution.
Evolution is a process in which resistance to change brings about more change.