Each of us has a protected zone two or three feet wide, swelling around the head and narrowing toward the feet. This zone isn't fixed in size: If you're nervous, it grows; if you're relaxed, it shrinks. It also depends on your cultural upbringing. Personal space is small in Japan and large in Australia. This safety zone, called personal space, provides an invisible spatial scaffold that frames our social interactions.

As Michael Graziano argues in The Spaces Between Us, it also organizes our social and emotional spacing, influences our facial expressions, and shapes our interactions with everyday objects including tools, furniture, and clothing. Even ordinary actions like walking are informed by a continuous under-the-surface calculation of threats and obstacles around the body - what Graziano calls a virtual Bubble Wrap of active neurons that fire and move us to action, even before we may be conscious of our course corrections in real time. Humans evolved a complex way of interacting with others and their environment, and The Spaces Between Us looks at how this infrastructure may have led to the first smile and to a host of other human activities, from tool use to courtship to a sense of self.

The book concludes with a case study of Graziano's son, who had heartbreaking difficulties developing a functioning personal space. Written with poignant narrative clarity, the book makes the case for the interested scientific public that this system in the brain is more than a fascinating scientific topic: It's deeply personal and shapes our human nature.