BEIJING, March 11 (Xinhuanet) -- The ability to put words together to express complex ideas was thought to belong only to humans, but now scientists reveal a primate other than humans can also express a variety of message by combining sounds into different sequences.

    The finding suggests this level of language might have occurred far earlier in evolution than thought.  Researchers focused on putty-nosed monkeys (Cercopithecus nictitans) in Nigeria. They studied alarm calls the males made.

    "To study alarm-calling behavior, I once dressed up as a leopard and approached a group of sooty mangabeys," recalled psychologist and primatologist Klaus Zuberbühler at the University of St. Andrews in Scotland. "The monkeys detected me, got very agitated, alarm-called at high rates, and a number of males approached in the low canopy ... aggressively displaying their large canines. At this point I was glad to be able to change species (by taking off my costume) and reveal myself. They looked at me with puzzlement, and then ran away silently. It felt good to be a human!"

    By three years of hard work trailing male putty-nosed monkeys, the researchers found the primates produced series of alarm calls that differed depending on the threat involved. For instance, a series of calls made up of "pyows" are a common response to leopards, while series of "hacks" followed by "pyows" are given to crowned eagles.

    By playing back recordings of calls at monkeys, the scientists unexpectedly discovered that males could arrange hacks and pyows to convey at least three different kinds of information to other monkeys — the event they witnessed, the identity of callers, and even whether they intended to travel.

    Most primates are actually limited in the number of signals they can physically produce because of their lack of tongue control.

    "The only way to escape this constraint may be to combine the few calls they have into more complex sequences," Zuberbühler said. "In other words, it may be 'harder' for non-human primates to evolve large repertoires than to evolve the ability to combine signals. Hence, the evolution of combinatorial signaling may not be driven by too many signals but rather by too few."

    Since the ancestors of humanity genetically diverged from ancestors of these monkeys some 25 million years ago, these findings suggest that some of the core abilities required for human language may be much older than had been thought.

    (Agencies)