Next we'll discover they were rendering that fat to grease their wheel axles with...
I think it's still reasonable to argue that Neandertals lacked certain capacities that we have, based on differences in the evidence from tools and art that's attributed to them vs Sapiens.
But IMO this would clearly have been a difference of degree, not at atomic shift. They were obviously _people_.
In recent years we've went from "completely primitive and segregated Neanderthals", to "oh, we share quite a bit of DNA with the Neanderthals", and "the Neanderthals engaged in complex symbolic thought", as well as "the Neanderthals were pretty advanced artists".
The current article is a further demonstration of that trend.
So it's fair to say that our original assumptions of the Neanderthals were profoundly flawed, and, as we go, we discover that they were different to us by a difference of degree -as you propose-, as opposed to the notion of being radically and binarily different.
In that vein, it is not a stretch to imagine that we were perhaps also completely wrong in our assumptions of their ability to communicate by sound, i.e. mastering languages.
Their DNA is up online, but you can also see these variants here: https://academic.oup.com/humrep/article/36/3/734/6071469
They were highly inbred and they were carriers for this form of Congenital Adrenal Hyperplasia (CAH) due to 21-Hydroxylase Deficiency. Even in its nonclassic form, this would have contributed to the low population numbers as any classic form would have been non-viable as well as resulted in evolutionary pressure to select for the genetic variants to compensate for the altered HPA-Axis. Neanderthals are most known for contributing to human specific DNA sets such as improved immune system, but if you go digging you will notice the larger pattern.
NCAH specifically results in higher neurogenesis. They were smarter. They also now had a bigger glucose preference and started to shift calories to grain. At some point between 130-70KYA there was enough excess calories from grain to not need to eat the dead. (see their teeth between this time) Admixture with modern humans occurs around 50-43KYA. These adaptations would have contributed to the loss of the mitochondrial DNA due to low female reproductive success compared to the higher male Neanderthal with female human success. The 2-4% that is found together is found together for a reason. They are incredibly valuable together.
This support for reduced HPA-Axis would have allowed for many other variants on the HPA axis and while not a single genetic variant, atypical HPA axis phenotype is associated with intelligence due to the enhancement in ability to detect unexpected events.
The glucose/grain preference with higher caloric density supported the higher population densities that occurred rapidly due to the Younger Dryas (last glacial period) and resulting agricultural and villages transition in Mesopotamia. These agricultural populations outcompeted other human groups while spreading the Neanderthal derived genetic variation.
Because humans can develop a zona reticularis in their adrenals (unlike marmoset which has partially solved this with an adaptation) the way HPA axis variants interact with steroidogenesis influences sexual differentiation and reproduction in homo sapiens there is constant push and pull.
It has been proposed that the advantage we wield which led to out-competing / interbreeding with them may have been a superior ability to starve - i.e. use fewer calories - during periods like the last ice age.
So my theory is that they could well have been more sophisticated in a lot of ways, but were just outbred.
https://www.nature.com/articles/s41380-024-02593-7
https://www.nature.com/articles/s41598-017-06440-4
It's far from conclusive, not representative of the majority of folks with autism diagnoses, and needs more replication and investigation. But it could be a thing. Speaking as a spectrum-y red-haired middle-european.
What language enables, in my view, is accurate communication through intermediaries. It makes a lot of difference whether you need to supervise someone through all the ways that cooking on leather can go wrong versus richly explaining those same failure modes and how to avoid them. The former pretty much prescribes that most complex knowledge will stay within a tribe or a close community, whereas a rich vocabulary allows knowledge to spread readily among trade routes.
In Jean M Auel’s Earths Children books the Neanderthals communicated via hand gestures and vocalizations.
I think any small groups of humans were just one virus away from extinction. Even we almost disappeared. A species that has a very low population for the entire species then all get sick that is bad even if all do not die. Your species loses genetic diversity and then another virus or even a large natural disaster strikes the group wiping it out. Maybe we just were lucky and survived not due to any skill better than other species.
While crows have "crafty" intelligence, neanderthals would be more apt at this.
But really, the logical first language would be gesture, an extension of already existing body language. And such language is employed by humans when hunting, at war, whenever quiet is preferred.
Even a gesture language of a few dozen concepts is almost automatic, pointing, waving, directional motions, hushing motions, pointing at your head, clapping, etc.
This being extended as full language in beings incapable of complex sound, seems viable.
If I had to guess basic sentence structure probably goes back to the beginning of homo. The differences between Sapiens and others is likely much more subtle. e.g. symbolism, myth making, abstraction or something like that.