By chance?

[OakTree500]

I apologise for the Giraffe analogy - I thought it was simple to comprehend, but transparently not for Jack.

Again, it's an example - but as you said:

"Im talking the near ancestors of giraffe, a normal sized mammal, w no long neck, no advanced circulatory system , no heart capability for hard pumping, no supporting musculature system. At this point you’re going to need a miracle sequence of mutations to complete the giraffe. Who feels lucky for those particular mutations to take place?"

We're not saying, one day there was one that was what you see today. The changes in evolution are tiny, and take millions of years to reach it's end goal. The rate at which any of these changes happened would have been miniscule to the naked eye, but they did happen [See Mister Agenda's link for the information].

For example, based upon the "giraffe is short in the beginning" idea:

The tree grows, Giraffes can eat it, lots of those plants die, thus not living longer etc

During all of this, random mutation is happening all the time - Some of them not helping. One maybe grew shorter, one maybe grew more leaves, either way it wasn't beneficial to helping the plant survive. Then some of those plants grow taller, lets say an inch for arguments sake. Some giraffes can still eat it, but others which were an inch too small even before this happened now cannot - they feed off of the smaller trees still, until they no longer can live [over the course of hundreds/thousands/millions of years] and die out, leaving only the larger ones to continue to populate/pass on their natural mutation in their genes.

And the cycle is just "rinse and repeat" for the next million odd years until we come to what you see today. It's not just necks, it's the whole shebang. Some were probably born with longer necks they couldn't support, but some survived who could do that, and passed on that mutation. It's a very long process, in larger animals that live longer at the very least, so it takes very small changes over millions of years to coincidentally come together for the "right" ones, where as every other animal will die off, also for the same purely coincidental reasons.

Again this can be physically seen in various insects that live/die very quickly.