National Geographic has just put up a story regarding a fossil skull that was dug up in Romania during World War II, in a mining operation. It was not studied in any depth until after that war, and was dated to around 33,000 years old. It was, and is considered "modern". However, another look at this skull, by several experts, including Erik Trinkaus, one of the leading modern Neandertal experts. The reexamination unearthed a groove at the back of the skull, which had apparently, previously been overlooked. According to Trinkaus, this groove is very common among Neandertals(but the Gentle Reader should remember that not all Neandertals exhibit all the traits attributed to them), but rare to nonexistent among other "archaics". And it's rare to nonexistent among most contemporary "moderns". But this skull exhibits this trait. And Romania is one place in Eastern Europe, where Neandertals and "moderns" are known to have at least coexisted. You can view the skull here:
Now it doesn't necessarily follow from all of this, that Neandertals and "moderns" interbred. My feeling is, that, because at the time, the populations of both groups were necessarily rather small. Which could have meant (a) that some members of either group did not find "within-group" mates for whatever reason, or (b) that neither group regarded the other as fundamentally "different" in the ways that count. However, those who disagree point to possible mutations or simply "odd" characteristics that pop up in some people now and again. The problem is, apparently "Neandertal" characteristics are turning up in a number of places where Neandertals and "moderns" were known to have coexisted. It seems to me that this is something which is beginning to happen with sufficient frequency, that those who lean on the "genetic" aspects, have trouble explaining away. Most of them just ignore such things. But if these traits keep turning up in places as diverse as Portugal and Iberia, the "no admixture" crowd is going to have to do a great deal of explaining.