I read New Scientist today. Their Letters section included the following:
From Gwydion Williams
Your Instant Expert on the evolution of language says the selection pressures that encouraged our heavy reliance on speech rather than sign language remain elusive (4 December).
I have never used sign language but it must be tricky addressing someone who is not already looking at you. I suppose there is no equivalent of shouting or whispering.
It would be worth consulting someone who habitually uses both, to learn more about the merits between the two modes.
Which is just all kinds of whaaaaat? Of course there's an equivalent to speaking softly or shouting! It's called "body language" and "facial expressions", not to mention how forcefully or how gently the signs are made. Duh? About the only point he actually has I think is how it's difficult if the person isn't looking at you, though how that's much worse than someone otherwise simply not paying attention, I don't know.
Additionally, the editor's response was:
Good point. The counter-argument is that there are certain disadvantages to speaking out loud, such as alerting predators and prey to your presence. It is also precluded in noisy environments
Which made me recall zompist.org's Language Construction Kit, wherein the point is actually made that spoken language tends to actually have a lot of built-in redundancy precisely because it helps overcome distortion, as from background noise.
I think the magazine is probably a bit better on its math and physics than its linguistics.
Either way... any thoughts on all this?