We belong to the primate order of the mammalian class of the animal kingdom. A distinguishing characteristic of primate evolution is the manner in which their large brains were acquired. There is wide agreement that these outsized brains were evolved not in response to the outer physical environment but to the inner environment of an intense hierarchical social structure. I propose that the changes that rendered apes into humans also took place in the brain as humans adapted to a momentous change in the social structure of ape societies. Our distinguishing characteristic of upright posture and the development of a widespread stone tool industry were both a response to the distinctively human social environment, which is the topic of this book.
Primates began forming groups some fifty million years ago. The hierarchical social structures that make up their meta-environment are actually comprised of so-called social emotions. Consciously felt emotions generated by the brain comprise the core of what is known as the mind. Like other primates, our mind is a social mind because our social behaviors and cognitions (ways of knowing and communicating) have evolved upon a scaffolding consisting of an invisible shared environment of social emotions.
Emotions are generally viewed in evolution as mere secondary, proximate vehicles with which to achieve ultimate behavioral adaptations to physical environments. For example, while the ultimate behavioral adaptation to the danger of falling off a cliff is to avoid cliffs, the proximate mechanism is the fear of heights. When I came to understand that that all primate social structures are made up of nothing but emotion and motivation, I realized that the most direct empirical evidence for the human social environment lies in the subjective experience of our own minds. So I set out to excavate the ancient social structures that had been the environments in response to which we became human.
Here is a quotation from Darwin’s last great treatise, The Expression of the Emotions in Man and Animals (1872), which is a pioneering work on the significance of emotion in human evolution along with his longstanding belief that answers lay in the study of domesticated animals.:
We have also seen that expression in itself, or the language of the emotions, as it has sometimes been called, is certainly of importance for the welfare of mankind. To understand, as far as possible, the source or origin of the various expressions which may be hourly seen on the faces of the men around us, not to mention the domesticated animals, ought to possess much interest for us.
In the last sentence of the first chapter of On The Origin of Species Darwin summarizes his opening case for the power of selection in the alteration of physical traits in domesticated animals:
Over all these causes of Change [from domestication] I am convinced that the accumulative action of Selection, whether applied methodically and more quickly, or unconsciously and more slowly, but more efficiently, is by far the predominant Power.
I have been similarly convinced of the power of selection on the domestication of emotional traits in dogs by research on the subject, but also by virtue of having benefitted from the wonderfully balanced emotional temperaments of a half-dozen German shepherds that were intentionally bred for that very quality. Of two other shepherds that were not, one died of a kidney malformation, and the other, at sixteen weeks first began manifesting an explosive rage disorder of a very specific nature. He would suddenly attack when: 1) he was fixated on “pos-sessing” something—in the culminating event it was a stinkbug haplessly crawling near him, and 2) he assumed (falsely) that, by virtue of merely entering the same room as he and his possession (the stink-bug), that you had expressed the intention of denying him this repellant creature. After he bit not only me, but other members of my family, I “selected out” the genes that underlay this pathological emotional wiring. There was no way that his behavior had been learned.
 It must be noted that most animals cannot be domesticated due to either excessive flightiness (deer) or aggression (zebra).
 The week after retiring from a career as a psychiatrist, I found myself in a dog psychologist’s office with my canine perpetrator. This would not be the only therapeutic modalty we tried, including residential treatment with a military trainer plus a hefty dose of Prozac, all to no avail.