Impossible to have a continuum without any idea of what sits at or at least near the edges, relatively speaking.
Not really.
Any continuous dimension — be it definite or indefinite, or even infinite — with an indistinct transition between any arbitrary points can be said to be a continuum, e.g. space-time continuum, dialectal continuum, and so on.
In this case we don't have any definite extents of the continuum, but from observation we can speculate that communication and language is not necessarily a diametrical of (human) communication versus no communication at all, and that there is probably no clear boundaries between the degrees of communication and language.
We
may or
may not possess such a complex capability for communication that the gap between humans and other animals is notable — I like to use Koko and Kanzi and counterpoints to such a speculation — but even so, it would not negate the observation that communication and language does not seem to be "stepped", but rather a continuum of varying capability.
Since we hardly understand animal communication as it is, it's very difficult to try and categorise different animals by their capability for communication and language, and even as complex as we might think of our human communication, I would dare say that it would be very arrogant to think of our form and state of communication as superior or even more complex ... we simply don't know yet.
However, it would probably be somewhat foolhardy to claim that communication and language is a landscape of peaks and valleys, rather than a continuous slope. Whatever Chomsky and others may say, I find it difficult to believe that our capability for language would have been as abrupt as some make it out to be.
That language itself could have grown non-linearly is nothing I disagree with, but that does not necessitate an equally non-linear growth in our inherent capabilities.
Perhaps that's the problem? The confusion of capability and the
emergent expression of said capability?