Evolution of Parietal Cortex in Mammals: From Manipulation to Tool Use
One of the hallmarks of human evolution is the extraordinary degree to which we can manipulate the physical world with our hands or with tools that extend or amplify our limbs. This manual dexterity coevolved with an expansion of posterior parietal cortex (PPC), which contains areas involved in programming voluntary movements, coding reach targets in multiple reference frames, and decision-making. To enable our body to interact with our physical surroundings, these fields must also construct an internal model of the physical self: our body's configuration, the boundary between our body and external physical objects, and the temporary expansion of that self as we wield a tool that extends our reach and manual capabilities. Such comprehension of where and what the self is and even the ability to manipulate objects and use them as tools did not evolve de novo in humans, but rather emerged from simple networks present in early mammals. In this chapter, we consider not only the structure and function of PPC in primates, but also include data from nonprimate mammals in an effort to understand the basic processing networks that were present in our early ancestors, and how these networks evolved and expanded in primates.
