Signing babies signal evolution of human language

In a discussion about the origin of human language and speech with my youngest son recently, I was uncertain how long ago it evolved and so I looked up the current state of knowledge in Wikipedia. The page on The Origin of Speech was comprehensive and fascinating. There seems to be considerable disagreement among the experts, with many plausible hypotheses being firmly shot down. Several things caught my attention that were new and intriguing.

But, for some motivating context, let me first scroll back to a reunion of university friends I was at in February. One of our number has mobility problems and his daughter, whom I hadn't met before, provided his transport and joined us for the meal. I sat next to her and found out that she earns a living by running sign-language workshops for pre-speech babies and their mums. It turns out that the babies are very adept, even creative, at signing. She had some lovely videos on her phone showing them performing. Signing frees them from the frustrations of not being able to communicate their thoughts and emotions, for the simple reason that they have not yet developed the delicate muscle control of tongue, lips and throat to produce the phonemes required for speech.

Returning to human evolution, here is a very approximate developmental timeline for hominins and their ancestors, measured in millennia:

• −2000 Dramatic enlargement of brain (widely accepted)
• −700 Learn to control fire (supported by archaeology)
• −350 to −150 Speech emerges, exact timing contested.

Interestingly the time gap between the growth of brain size and the control of fire makes it hard to the sustain speculation by Richard Wrangham and Rachel Carmody that cooking food freed up chewing time and digestive energy for other developments, in particular, a larger brain. However, a palaeontologist who has been carefully analysing the sandstone layers in the Olduvai Gorge has discovered markers for bacteria that can survive 80 - 90 degree C, suggesting there were once very hot springs in that volcanic region that could have been used for cooking - there are several instances of peoples using that way of cooking even today. Another interesting idea reported in a recent issue of The Economist, suggests that intense radiation from violent cosmic events in our neck of the Milky Way around 2.5m years ago led to the destruction of the earth’s forests and forced us down from the trees. In the grassy plains, bipedalism became an evolutionary advantage and freed up our hands for new creative purposes

I found the following ideas in Wikipedia particularly striking:

1. Humans are the only animals that can use language independently of modality -- we can switch from speaking to typing or to signing (once learnt) at the drop of a hat. Apes, including chimps, can combine modalities (e.g. the visual and aural) in their communication but they cannot separate them. Hence the ability human babies have to sign and thereby learn to communicate before they can speak. 

2. Chimps and other apes make strenuous efforts to avoid being deceived by their fellows, relying on signals that cannot be faked (for example, in the way a cat cannot dissemble a purr). This militates against the use of language because “words are cheap” and language is easily used to deceive. There have to be some other signals or social forces that forge trust without relying simply on words.

Two speculative thoughts:

(i) There is obviously a huge advantage, both to the individual and the group, in having a mental view of the present that is integrated with the past through memory and projects into the future with the formulation of plans for such things as social activity, making tools and hunting. I suggest that this is what the bigger brains allowed.

(ii) The bigger brains also allowed the beginnings of what we would call consciousness because the brain needed a symbolic way of representing the past and modelling the future. These representations led to the development a pre-language -- the language centres are large and complicated it seems – and this only found full expression in speech after the very slow evolution of the vocal system, which co-opted components of the mouth and throat for the wide range of phonemes we can make today. All of which suggests that a proto-language developed long before speech and perhaps explains why it is independent of the means of expression.