[PeterisP]

"There's literally no way to know if that was true" - we don't know now, but hypothetically in the future, wouldn't it be plausible to determine such traits from their DNA? We have a full DNA sequence, and wherever (and whenever, in the future) we know what impact particular genes had on some traits in primates, we can check how the neanderthals had it.

Heck, it would not get attempted due to ethical issues, but technically it might be even plausible to clone a neanderthal using a human surrogate mother, there has been some work in cross-species cloning.