No problem accepting adaptation in Nature...
But to say a fish crawled out of a swamp and eventually walked upright as something else that's a different hill of beans.
Precisely.
The biggest problem with that portion of the Theory of Evolution is two-fold. One: Apes have sufficient intelligence. They are capable of living in communities, making tools and using them, and they have the ability to adapt, without evolving, to most climates of the world. So can we. However, once these are in effect, the need to walk upright and build buildings seems almost superfluous. Why bother increasing the complexity and the potential for disaster, when a perfectly capable mammal already exists?
Two: There had to have been a first human. Sure, there were the Neanderthals, but someone had to be first in being a human as we know it. Meaning that there was, at one time, only *one* human. Now, even today in our "civilized" world, there is hate, prejudice, genocides. Back then, I can only imagine that it was worse, thanks to the trends back in time (the further in the past you look at, the more of this there is).
Excuse me for using the classic "what are the odds" argument, but this bears looking at. Let's say that in a family of Neanderthals, the first
homo sapiens sapiens was born. The chance of this happening are... well, the genetic difference is about 0.5% of our DNA. Our DNA contains 3 billion base pairs. .5% of that is
150,000,000 base pairs. The odds of all these changes occurring, at once, is 1/150,000,0002, or:
1/22500000000000000
(Or is it "150,000,000!"? If so, the denominator is even larger...)
Okay, now, this baby is born. I can't give definitive odds on how likely it is that a completely different baby is accepted by their parents (even today we don't always accept differences from the norm), the chances that a sufficiently similar baby of the opposite gender is available for procreation, the odds that they
will procreate at all, and the chances that both are fertile and healthy and produce offspring. However, the odds I've already given are so out of this world that I can't wrap my mind around it and accept it.