Jared P. Taglialatela, Jamie L. Russell, Jennifer A. Schaeffer, William D. Hopkins
PLoS ONE 6(4): e18852. doi:10.1371/journal.pone.0018852
What is being done here is to find out how human language evolved by looking at similar behavior in chimpanzees. Studies have shown chimp hand gestures and between individual vocalization as two possible candidates for an origin of language in a common ancestor. This is because both of these behaviors are flexible enough, plastic enough, to evolve into human language. This has led to two competing theories of language starting from either vocal or gestural signaling. To see if either of these theories work the authors investigated activation in a chimpanzee brain region that shows activation for language in humans. The result is that both behaviors activate this region. The suggestion is that human language origin is bimodal.
Modularity is a powerful concept in biology, yet biological entities can be both modular and highly connected. In this case, what seems to be two separate behaviors may share the same brain connections. Language may have evolved through a double feedback of site and sound. This is conversation, communication between individuals.