Consider a species. Without some particular mutation, its members have quality A. Suppose that quality B is better for the survival of any individual member of the species. If one member possesses quality B, natural selection could take over.
What if B is preferable to A, but the intermediary stages are not preferable to either A or B? Can a species go from A to B?
Say an organism has 4 legs but having 6 would be advantageous. Could it get to 6 without some disadvantaged intermediate forms? Or is there a way for a single genetic mutation to result in a one step change? Also, if no organism has ever made such a transition then I suppose it can go without explanation. But then maybe something went from 6 legs to 4, or something.
I hope this isn't too rambling. Kindly,