Bones don't deform that drastically while decomposing and they're relatively easy to tell apart when intact (there's pictures of comparisons available). Trained people can work wonders with even the smallest fragments.

But, as always in science, it is best if multiple avenues of inquiry point to the same direction. You can carbon date (older than 1 million years? no modern human) and also look at the situation where you find it (cultural techniques known not to be practiced by Neanderthals for example).

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I don't understand. Are all Neanderthal bones found in caves? If bones decompose quickly outside of caves and if all Neanderthal bones look similar they could just be human bones decomposing in caves and we've never observed it before to see the changes as they happen. How could you rule out them being human bones decomposing and say "bones don't deform that drastically while decomposing" if it's maybe something we've just never observed? Is there any slam dunk evidence that shows that Neanderthal bones are indeed Neanderthal bones?

There is genetic evidence extant in the genomes of large populations of humans and in DNA we have been able to extract from Neanderthal remains:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4072735/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2860157/

It is also notable that while there was SOME genetic input from Neanderthals into the modern human genome, there are no Neanderthal genes on any modern human Y chromosome- suggesting that it was either impossible for male Neanderthals and female modern humans to breed at all or that any such offspring produced were sterile like mules- a genetic block to fully interbreeding that points to a genetic basis to call them a different species.

We also have a lot of examples of modern human remains that have spent time in a wide variety of conditions, and none of them seem to deform in ways that give them the morphological characteristics of Neanderthals.

A picture says more than a thousand words in my opinion.

Check out this comparison of a human skull and a neanderthal skull:

https://en.m.wikipedia.org/wiki/Neanderthal_anatomy#/media/File%3ASapiens_neanderthal_comparison.jpg

I think it's pretty clear that the right is not from a human.

Have we ever found human remains in similar conditions that Neanderthal remains have been found in? Like in a cave decomposing? Have Neanderthal remains always been found in caves? If there have been found human remains decomposing in a cave and the remains did not look like a Neanderthal I think that kind of answers my question since then two different things have been found.

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