Geographical isolation would have more of an impact on speciation if it was an organism that reproduced sexually. If a positive mutation were to occur in an asexually reproducing organism that allowed it to survive better, evolution would be very sudden. There are many factors that can impact whether an organism is more fit and I do believe geographical differences can influence this. If the climate of an area suddenly drops but one organism can survive, they will pass their genes on and the rest will not.
One example of a positive feedback loop in childbirth is contractions. When the contractions start, they produce oxytocin, which stimulates stronger contractions, which produce more oxytocin.
