I was hoping for some sort of explaination.

When I consider all the places that a mutation can occur in the DNA (3.2 billion base pairs in humans)

And when I consider how many beneficial mutations are need to add up over the future generations to form a new body part (major morphological change)

I wonder how it is possible?

It seems as if these mutations would have to occur in a precise location. I am told that these mutations are random, so how does an animal with several billions base pairs over come the odds against repeated mutations occuring to the point that the last mutation is added to over and over again in future generations?

E=IXR

Because nature brutally kills everything with a disadvantage. There's a HUGE attrition in nature.

I don't remember the full statistic, but it's stunning. I'm vaguely remembering that if each offspring of a butterfly survived (i.e., no resource competition and no detrimental mutations), the mass of butterlies would outweigh the world in couple years.

That's a LOT of baby butterflies. And you know what? At any time, there's a huge number of butterflies being laid. However, due to ferocious natural selection, only the best (and lucky) survive. All those quadrillions of mutuations that need to occur to get a 'lucky' one are not so unlikely when you consider the growth rate.

Thanks for the rweply, but I think you missed the meaning of my question.

I keep getting asked how the mutations add up, or maybe I should have asked with all the places for a mutation to occur, what are the odds of another occuring in the portion of DNA that is "evolving"

E=IXR

All changes in DNA don't require mutations. The perfect example is that English moth. The darker color was not a mutation, it was a natural variation. Over time as the lighter moths are killed off, moths become darker, and the darker moths will sire even darker moths along with lighter moths. How do the moths keep getting darker and darker? All genes have a natural variation. How does a Chihuahua exist? Did it take many, many mutations to turn a wolf into a Chihuahua? No, just natural variations. Slowly, over many generations you can fine tune these natural variation just like evolution does over a geologic time scale.