One, two, three…uh…many.
Over at American Scientist, Marc Hauser has a nice article on the arithmetic abilities of humans compared with other animals, such as rhesus monkeys:
Studies of rhesus-monkey foraging decisions indicate that animals spontaneously, and without training, exhibit rudimentary numerical abilities.
From a comparative perspective, the limit on spontaneous number estimation in rhesus monkeys based on looking and foraging is interesting because it parallels the limits of human infants. It also corresponds to the range in the syntax of natural language: Human languages tend to have words for one, two and three and use an expression such as many to denote entities greater than three. Such convergence suggests that the brain mechanism underlying spontaneous numerical estimation is shared across a diversity of animals.
This hypothesis raises several crucial questions: First, are there conditions under which more sophisticated numerical capacities can be elicited in animals? And what social or ecological pressures would favor a mind capable of more precise numerical quantification? The answer to the first question is “yes,” but in order to fully comprehend how and why, we must consider the second category of experimental approaches, those that involve extensive training.
But let’s get to the practical aspects of this, which is that I can possibly train my cat to bring me more than one beer at a time when I’m out on the deck reading. “Good kitty—can you say, ‘six pack?'”