Where are the transitional forms. Where are the long chain of human anscestors who had first a little bump, then the next one had a slightly larger bump, then the next one had the beginning of a knuckle, etc etc etc.
Where are all the transitional forms?
And so, most likely, would their kids. That one of the cells that's supposed to become the middle finger splits in two when it shouldn't and thus produces two middle fingers is not due to a genetic change, but due instead to an 'errant' split in fetal development.
You do raise a somewhat valid point in that subtle changes can lead to discrete effects. As a simple example, the number of offspring a female of a species will normally have at once is determined genetically, and yet the females of any species will almost always give birth to an integer number of young.
Even a trait like 'number of simultaneous young', however, could have intermediate states; between a species whose average litter was three and one whose average litter was four could quite easily be one whose average litter was 3.5 (about half were 3 or fewer, and about half were four or more). Any individual pregancy would result in an integer number of young, but the species' average need not be an integer.