I think it's all about abstraction. Our language is highly abstract, so we can express complex thoughts by putting different words together and use a syntax. Such a sentence cannot be devided without losing it's meaning.
Most life forms DO communicate, even bacteria do. But usually one sound/gesture/smell/etc has one meaning.
Of course, the transition is smooth, as is evolution. So there won't be any exact definition.
Ok, speech may have developed thus far because these frequencies were available. But a sophisticated ear apparatus does not appear instantaneous, it takes ages. And there must be a reason for it (an advantage, actually).
In terms of evolution, things have to go hand in hand.
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I think it's all about abstraction. Our language is highly abstract, so we can express complex thoughts by putting different words together and use a syntax. Such a sentence cannot be devided without losing it's meaning. Most life forms DO communicate, even bacteria do. But usually one sound/gesture/smell/etc has one meaning. Of course, the transition is smooth, as is evolution. So there won't be any exact definition.
Ok, speech may have developed thus far because these frequencies were available. But a sophisticated ear apparatus does not appear instantaneous, it takes ages. And there must be a reason for it (an advantage, actually). In terms of evolution, things have to go hand in hand.