OKay. For instance (me and my all-knowing mind, d'oh) let's take you, presently. Let's take your blood brother (assuming you have one) born of your parents. Now, you marry some girl and have kids by her and so on and so forth. You'll have fairly normal generations of Eon (ar ar ar ar). Now. Your brother. Let's say you had a sister. Well...he marries her (let's assume we're in a Huxleyan fantasy world where stuff like that happens) and has kids by her. Ehh. Different. Right away. It shows. There are problems. You take an X and X you get an XX, so the genetic screwups are doubled in your child. LEt's assume they have two kids, a girl and a guy, who marry each other and then have more kids. Well there's an XX and a YY. So now we have XYXY. BOTH problems in the kids, doubled. And so on and such forth.
Pretty soon you'll have something like ghouls in the family line, but you breed normal healthy stock because they take from other genes that are normal and not immediately related. Why? The problems of your parents are passed on to you (and not necessarily receded at all times) so your brother and sister have the same probs. Well then they exemplify them in their kids. ANd they the same, so that the healthy genes of the family are rather hidden in some kind of entropic monstrosity you can call your great-great-great-great-great-great grandniece.
NOW. Let's assume Neanderthal is the same (as we can only do). Neanderthal is the byproduct of either of these: disease (caused by say, lack of certain vitamins/minerals that others may be more disposed to) or inbreeding. Neanderthal resembles human in shape, more than he does an ape. He's just a diseased human. Now let's take someone with a severe case of oh, say, osteoarthritis. And we'll give him scurvy, too. For fun. That dude looks screwed up. And let's say he hunched. And let's say he's a Dane. His skeletal form WILL resemble a Neanderthal's. Check it. Maybe genetic differences, sure (You couldn't show a Jew to his five-thousand year old ancestor. He'd laugh at you. The differences are TOO different to even think they're related. But maybe you could see similarities between yourself and Great-Grand Uncle Crawdaddy, because, you know, he's not too many generations different from you. Yeah you got his pug nose.).
Take a Cro-Magnon...he looks like a strapping, fit, modern-day human. In fact, maybe he is! He's stocky, he's well-built. Hey, maybe he was fit? Just a few thousand years old. Like five, or six. Maybe three? Jews are rather short. But they're tough. Living in the middle of a desert working in slavery will do that to you. But then they get free, and they're more healthy, and more and more they resemble humans.
Now for goodness sake. Take a body and dump it in Mideast. It will be ravaged. It happened to an elephant (this one I can cite, Natural Environment Research Council, p. 4, Spring 2002) there. Dump it anywhere. Decay, scavengers, insectia, disease, environment, WILL waste you away to a few bones. And what are fossils? Bones.
Why don't we see kangaroos in the Middle East? Or at least, somwhere in between there and Australia? Or their BONES at least. I mean, evolution says it would take millions of years to make em, and about as long to bury them under the sands of time. So show me a kangaroo fossil from Turkey. Or Afghanistan. I'll be happy. Kangaroos DO exist. And all things that are now came from something before, did they not? Eventually coming from condensed hydrogen, right?
WHY don't we see kangaroos in the Mideast? I know...a government conspiracy to hide the truth of evolution is out, and I, Fox Mulder, WILL find the truth. I know they're taking kangaroo skeletons and moving them to Australia. Who's with me? Scully? Eon? How about it? Help me find the truth. Trust no one, Eon. Trust no one.
Sorry. Couldn't help it there. Show me a kangaroo, or, heck, a WOMBAT, and I'll be happy (also explain how a wombat's pouch knew to evolve inwards, rather than outwards, like on a kangaroo, because wombats are low-dwelling critters...evolution knew that? Their genes told them that they lived on the ground? And so evolved?).
So humans are different and varied. Cro-Magnon, Neanderthal, Ergaster (now called non-existent, but not too long ago taught as pure fact, now actually paired along with erectus...how long before erectus and sapiens are one and the same, as "fact?"), Erectus, Sapiens...we're all one and the same? Different structures, different bone frames, different appearances, different skin, different features, different genes...still one and human. Prove to me, please, that Neanderthals are positive of human evolution.
On a sidenote, I don't think I did overly well explaining my point to you, Eon, but hey, I'm just 15 so cut me some slack. I'm thinking from sources I've read (but, alas, adolescent lackadaisical apathy set in and I forget to cite, save that elephant one) and my own mind to formulate this...and I think I pretty much hit on the nail as much as I can.