What was it like living in one of these early hominin groups? In my imagination, I picture becoming aware of a continuous chirping sound threading up from below while hiking on a promontory high above the East African savanna three million years ago. After lying down with my binoculars to examine the vast plain beneath me, I am astonished by the sighting of two groups of grass-eating apes, separated by about a quarter of a mile. I am utterly charmed and fascinated that I have discovered two herds, all harmlessly crouching and munching together. From the very beginning, and steadily increasing, I have a profound sense that these creatures are deeply unique. I finally see two of these three-to-four foot animals (presumably mates) stand up straight and walk over to the other group to join them, but that is the least of it. It is subtle at first, but once recognized, undeniable: I become aware that the individuals in each group as well as constantly vocalizing are all simultaneously gesturing to each other. They emit a continuous emotional intensity that causes within me a growing sense of foreboding—of fear. As harmless and closely comfortable as they are with each other, the thought occurs to me, that if they were to discover my presence, all that harmony might instantly amalgamate, and they could become extremely dangerous to an outsider. So, fearing for my life while fatally drawn to them, I furtively watch them hidden in my lofty perch. For two whole days, I am tortured by my complete inability to pin down what it is about them that both terrifies and enthralls me. Gradually I focus on how intensely in tune they are with one another without a hint of dominance or hierarchy. Each group will be doing different things, but very differently from the lazy pace of chimps in a zoo or from ordinary herd animals in which reactions to the environment are simultaneous. Then it hits me like a thunderstone. The individuals in these groups are not just cooperating with one another; the entirety of the behavior in these two groups is directed and coordinated as if both are part of a single creature.
Read another good excerpt here.
 Hominin hand axes were called “thunderstones” in the middle ages. They were thought to have dropped from the sky having been somehow produced by thunder and lightning.