Imagine grabbing a piece of paper between your thumb and index finger. Maybe you already are, as you turn this page. We use this type of forceful, pad-to-pad precision gripping without thinking about it, and literally in a snap. Yet it was a breakthrough in human evolution. Other primates exhibit some kinds of precision grips in the handling and use of objects, but not with the kind of (a) efficient opposition that our hand anatomy allows. In a single hand, humans can easily hold and manipulate objects, even small and delicate ones, while adjusting our fingers to their shape and reorienting them with (b) displacements of our fingertip pads. Our relatively long, powerful thumb and other anatomical attributes, including our flat nails (which nearly all primates possess), make this (c) possible Just picture trying ― and failing ― to dog-ear this page with pointy, curved claws.

With a unique combination of traits, the human hand shaped our history. No question, stone tools couldn’t have become a keystone of human technology and subsistence (d) without hands that could do the job, along with a nervous system that could regulate and coordinate the necessary signals. Anybody who’s ever attempted to make a spear tip or arrowhead from a rock knows that it (e) excludes strong grips, constant rotation and repositioning, and forceful, careful strikes with another hard object. And even with a fair amount of know-how, it can be a bloody business.

* primate: 영장류 ** anatomy: 해부학 *** subsistence: 생계