mathematical puzzles or to communicate using human language then it is usually possible to recognize what intelligence it shows.

But if one just observes the normal activities of the animal it can be remarkably difficult to tell whether they involve intelligence. And so as a typical example it remains quite unclear whether there is intelligence associated with the songs of either birds or whales.

To us these songs may sound quite musical—and indeed they even seem to show some of the same principles of organization as human music. But do they really require intelligence to generate?

Particularly for birds it has increasingly been possible to trace the detailed processes by which songs are produced. And it seems that at least some of their elaborate elements are just direct consequences of the complex patterns of air flow that occur in the vocal tracts of birds.

But there is definitely also input from the brain of the bird. Yet within the brain some of the neural pathways responsible are known. And one might think that if all such pathways could be found then this would immediately show that no intelligence was involved.

Certainly if the pathways could somehow be seen to support only simple computations then this would be a reasonable conclusion. But just using definite pathways—or definite underlying rules—does not in any way preclude intelligence. And in fact if one looks inside a human brain—say in the process of generating speech—one will no doubt also see definite pathways and definite rules in use.

So how then can we judge whether something like a bird song, or a whale song—or, for that matter, an extraterrestrial signal—is a reflection of intelligence? The fundamental criterion we tend to use is whether it has a meaning—or whether it communicates anything.

Everyday experience shows us that it can often be very hard to tell. For even if we just hear a human language that we do not know it can be almost impossible for us to recognize whether what is being said is meaningful or not. And the same is true if we pick up data of any kind that is encoded in a format we do not know.

We might start by trying to use our powers of perception and analysis to find regularities in the data. And if we found too many regularities we might conclude that the data could not represent