Why are spoken languages more common than signed languages?

Question

As I understand, there is no essential difference between spoken and signed languages. Both have the same kinds of phonetic, morphological, syntactical and semantic complexities, both are prone to ambiguities, both change over time etc. The main difference is one of medium.

Spoken languages have, of course, some advantages over their signed counterparts, as the possibility to communicate without visual contact. But signed languages have, in turn, other advantages over the spoken, like higher "bandwidth", i.e., information is conveyed by multiple channels at the same time (hand shape, hand position, eye gaze and head nodding).

In spite of that, spoken languages are much more common than signed languages. And most of the latter have developed at "artificial" environments, like schools for deaf children. Why don't we see, for example, isolated tribes (with hearing and speaking people) that haven't developed any kind of spoken language, but have a rich tradition of signed languages, instead?

Answer 1

There's a lot of types of signed languages (some more like sign vocabularies), so not all have the same properties. Also, they are not limited to deaf communities. Most famously, the Plains Indian Sign Language was used both within and across cultures. It certainly wasn't just a sign encoding of spoken language which is what many non-deaf sign languages are.

However, there are no instances where signed languages developed prior to spoken languages. Nor are there non-deaf communities that only use a sign language as opposed to spoken languages.

Again, why questions in linguistics are not a safe place to go but if I were to venture a guess, I would be very skeptical about any explanations relying solely on communicative utility. You can make the argument that in many situations (combat, hunting) signed language would be much more appropriate.

I would suggest that a better candidate for an explanation would be a simple co-evolution. Symbolic communication was simply associated with vocalizations from the start. Since the origins of language have as much to do with socialization and expression of emotion as communication, I would imagine that mapping symbolic meanings on vocal expressions is more productive than with gestures (although paradoxically, now, gestures are used mostly to supply affective content - although in a much more subtle way than just emphatic waving around of hands). So any grammaticalization would happen on the vocal part of language first. But it's a completely speculative guess (although one that would probably have been endorsed by Jespersen).

Answer 2

The biggest problem with signing is that you can't talk to a person without first getting their attention. If they don't actively look at you and attend to what you are saying, communication is impossible. Think of all the times you have yelled at/spoken to someone who may not even been aware of your presence; or public address systems, that communicate with everyone within earshot (not eyeshot) Signing is a co-operative venture; speaking is unilateral.

Answer 3

As with the other respondees here, I do not know the answer to your question, but can speculatively suggest one main one.

All natural languages accommodate the fact that there is a pay-off between time and effort on the one hand, and informativity or cognitive effect on the other. So we will prefer a shorter and less energy- or time-consuming way of saying something given a choice and an identical cognitive effect.

It is simply much more calory-expending to use sign language than to use an air-pressure mechanism to communicate.

However, the reasons may be multi-factorial in any case. So a preponderance of factors weighing in on one side or th other may make a difference. One other factor wich may benefit an air-pressure mechanism (i.e. sound) is that a lot of spoken language occurs when there is little or no light available, which is clearly very useful.