That dolphins don't have abstract language was recently established in a very elegant experiment. A pool is divided into two halves by a net. Dolphin A is released into one end of the pool where there is a mechanism. After a while, the dolphin figures out how to operate the mechanism which causes dead fish to be released into both ends of the pool. Then A is transferred to the other end of the pool and a dolphin B is released into the end of the pool that has the mechanism. The idea is that if the dolphins had a language, then A would tell B to operate the mechanism. However, it was found that the average time for B to operate the mechanism was the same as for A.
I've just updated my paper on "How long before superintelligence?" (http://www.hedweb.com/nickb/superintelligence.htm) and among other things I added the above footnote, for I can't find a reference. Does anybody know the source?
Nick Bostrom
http://www.hedweb.com/nickb n.bostrom@lse.ac.uk
Department of Philosophy, Logic and Scientific Method
London School of Economics