Our closest relatives, chimpanzees and bonobos do not generally form fists, and the researchers think they are unable to: when a chimp curls up its fingers it forms a doughnutshape.
The DIs wore their hair long and pinned up in "sock buns, " a Marine Corps specialty that required snipping off the toe line of a sock, rolling the fabric into a doughnutshape, and wrapping and winding a ponytail's worth of hair around it.