from Richard Klein and Blake Edgar’s The Dawn of Human Culture:
The Neanderthals are fascinating because they were so much like us and yet so different. Before we abandon them completely, we want to address one well-known speculation for what could explain the difference. This is the possibility that they possessed only a limited ability to speak, that is, to produce the kind of rapidly spoken, phonemic speech that characterized all historic peoples. Historic cultures may vary greatly in their complexity, but historic languages do not—they are all equally sophisticated and they can all be translated one from the next, meaning that any one can be used to express any idea, however intricate.
What about Neanderthal language? The truth is that we don’t know. We can only imagine that Neanderthals had a system that was far more complex than that of chimpanzees or for that matter than the systems of the the australopiths, Homo ergaster, and probably even Homo heidelbergensis. But does that mean it was as sophisticated as modern language? One clue may come from the position of the voice box (or larynx), which is crucial for the production of the entire range of sounds that all modern languages require. In apes and newborn humans, the voice box is located high in the throat, restricting the range of possible sounds. A major advantage of this position is that it permits apes and human infants to swallow and breathe at the same time, reducing the risk of choking. The voice box begins its descent in humans between the ages of 1½ and 2 years, and since this significantly increases the risk of choking, there must be a countervailing natural selective benefit. The most obvious one is the newly created ability to produce all the sounds that are essential for phonemic speech, and no one doubts the survival benefit of speech. The position of the voice box is related to the shape of the skull base—flat in apes and modern human infants and arched upwards or flexed in modern human adults. On the three Neanderthal skulls that are well enough preserved to show the skull base, it appears to have been flat, and this might mean that Neanderthals could not have produced speech as we know it.
Against this, however, we must consider the tongue bone (or hyoid), which provides hard support for the voice box and which differs significantly in shape between apes and modern humans. Only a single tongue bone is known for the Neanderthals, but it’s a dead ringer for its modern human counterpart. And we must also consider the Neanderthals’ African contemporaries—the modern or near-modern people, who, unlike the Neanderthals, included our ancestors. They had flexed cranial bases, but we will see that in virtually every detectable archeological respect they were no more modern than the Neanderthals. So, if they could speak in a fully modern way, the ability doesn’t seem to have fostered full-blown modern behavior—the dawn of human culture to which the title of this book refers. A newly found capacity for language may still have prompted fully modern behavior, but if so the capacity must have been rooted in a brain change. We argue later that such a brain change is the most economic explanation for why modern human behavior emerged and spread so quickly.