In the early 1970s, culture and human-development researcher Patricia Greenfield, PhD, found an interesting pattern: As young children begin putting together objects, such as nesting cups, they develop strategies that parallel methods for combining words, and they develop them in the same order. Further work studying apes who were learning to communicate using arbitrary visual symbols showed the same pattern: They not only develop parallel strategies in the same order in both domains, but their upper level of complexity is the same for combining symbols and objects.
The University of California, Los Angeles, psychologist's ideas were controversial: Adding neuroscientific evidence, she argued that the same brain area controlled both the linguistic ability to form combinations, as well as manual ability to form combinations, thus linking hand movements with language in some very basic evolutionary sense. She further asserted that the brain area shared by physical action and language was Broca's area, a part of the brain traditionally associated with human language
Then Greenfield learned that researchers had found mirror neurons--nerve cells that fire when primates not only produce a goal-directed action but also watch someone else produce the same action--for manual actions (such as grasping) in the F5 brain area in monkeys, a Broca's homologue, and in Broca's area in humans. "Eureka!" It all made sense to her.
Everything researchers were learning about mirror neurons, particularly their ties to imitation and goal-directed actions, seemed to mesh with Greenfield's work on language development in humans and apes: Her research shows that imitation is the first phase of conversational competence in humans, chimpanzees and bonobos, and that symbolic communication begins with the expression of goal-directed action in these species. Greenfield says mirror neurons connected and validated several strands of her research. What's more, by providing a neural foundation for key cultural processes, such as imitative learning and the attribution of intentionality to others, mirror neurons provide a kind of "magic bullet" for understanding the evolution of culture, she says: "It gives the study of culture more of a hard-science foundation, and that can only lead to a better and truer understanding of how we all evolved to be the way we are."