A fundamental problem for understanding the evolution of human language has been the lack of significant parallels among nonhuman primates. Several studies found that nonhuman primates do not have a vocal tract. However, such points have been challenged by recent research, suggesting that nonhuman primates may after all be valuable models for understanding the evolution of speech and language. The main animal model for vocal learning has been birdsong acquisition. However, there are crucial differences between birdsong acquisition and human language learning. And given some severe limitations, for example, birds have two vocal organs and do not have the flexible supralaryn-geal structures that facilitate speech, of birdsong as a model of speech, there is value in seeking other appropriate parallels among mammals. Recent studies on macaques and baboons have shown that the vocal tracts of these monkeys can produce a full range of human-like vowels. Turn-taking is a key to fluent human conversation and has been thought to be unique to humans. One study found that captive chimpanzees increasingly share resources when resources are diminished. Collaborative turn-taking for food has been seen in other primates. These recent studies show that there is value in looking for the evolutionary origins of speech and language in nonhuman primates. Human speech and language are highly complex systems with multiple components. Thus, to fully explain language origins, researchers must seek multiple models that represent both diverging and converging evolutionary processes. There may also be differences among primate species in the developmental processes that parallel human language acquisition. However, no studies have yet described vowel-like sounds in these monkeys, so marmosets and tamarins may be useful primarily for developmental studies. It is probable that early humans faced evolutionary pressures that differed from those encountered by other primates and that have made our complex communication system adaptive. Language may have been important for coordinating activities in large cooperative groups. If individuals can thrive without complex vocal signaling, there would be little motivation to push the communication further. Different sensory and motor systems may be important. We tend to evaluate language through a vocal / auditory system, whereas research on apes is beginning to illustrate the complexity of gestural communication. Nonhuman primates do not talk, but we should not expect them to. Each species has its own adaptations for communication. Nevertheless, there is much about language evolution that we can learn from nonhuman primates, provided that we study a variety of species and consider the multiple components of speech and language. The example of birdsong acquisition is mentioned to_____.