CHAPTER 1
The Evolution and Ontogeny of Deep Social Mind and the Social Brain

ANDREW WHITEN

INTRODUCTION

A core hypothesis of the theory of Deep Social Mind (DSM) is that the extraordinary evolutionary success of our species is explicable not through some one critical mental attribute (intelligence, culture, language) as is often proposed, but rather by an adaptive cognitive complex that involved a whole suite of interrelated refinements to our ancestral ape psychology (Whiten & Erdal, 2012). More specifically, the proposal is that the human mind became more profoundly and deeply social than the minds of our primate relatives and ancestors in a cluster of dimensions, involving enhanced cooperation, egalitarianism, culture, mindreading, and language. This has obvious implications for understanding both the underlying neural machinery of the social brain that implements these functions and for the developmental psychological processes that build deep social minds in each generation - the foci of this volume.

The concept of the social brain - itself multistranded, as we shall see - has its roots in the study of primate social complexity, and I begin this chapter with an overview of the rationale and scope of the key ideas and empirical findings of this research field, with a focus on the variants variously described as the "social intellect hypothesis," "Machiavellian intelligence hypothesis," and "social brain hypothesis." This leads in turn to what may be regarded as part-offspring and part-competitor of these hypotheses: the "cultural intelligence hypothesis." The latter also forks into interesting subcomponents, as we shall see.

These hypotheses and the findings that bear on them provide foundations for the subsequent part of the chapter, which addresses the scope of Deep Social Mind in its particularities. I review both the characteristics that differentiated evolving human minds from those of their primate ancestors, and what we know of those ancestral minds that so importantly provided the foundations for these special human achievements. We can then address the ontogenetic development of Deep Social Mind in humans, and its foundations in the life histories that characterized our primate ancestry.

The intertwined concepts of social intelligence and social brain have been increasingly influential in research endeavors across the behavioral and cognitive sciences. Table 1.1 is offered to illustrate this, showing the numbers of relevant publications in 5-year blocks during the past quarter century. The accelerating pace of work in these domains is clear. Accordingly, what follows below is necessarily highly selective. My aim is to offer overviews of major themes and discoveries that link comparative, evolutionary, developmental, and neuroscientific studies.

Table 1.1 Articles indexed in Web of Knowledge according to key words in title or in topic field.

*SOCIAL INTELLECT = social intellect or social intelligence or Machiavellian intelligence.
[Note: Searches use operator "Near/0" to include paired terms only when adjacent, e.g., "social brain."]

PRIMATE MACHIAVELLIAN INTELLIGENCE AND THE SOCIAL BRAIN

In "The Social Function of Intellect," Nick Humphrey (1976) is generally recognized as the first to clearly articulate what came to be called "the social intellect hypothesis." The key idea, a radical one at the time, was that the acknowledged distinctive intelligence of nonhuman primates (henceforth "primates") was not so much an evolutionary product of dealing with physical problems in their natural lives, like how and where to best forage or avoid predators, but was rather an adaptation to grappling with the special complexity being revealed in primates' social lives. Humphrey's proposition had been prefigured by some earlier glimmerings of the significance of primate social complexity (e.g. Jolly, 1966) but it was Humphrey who expressed the theory most explicitly and fully, leading a small but growing band of primatologists to shape their empirical work around it in the years that followed.

Over a decade later there were sufficient developments to fill a book on the topic, and Richard Byrne and I assembled Machiavellian Intelligence (Byrne & Whiten, 1988) to do so. The title was created in part under the influence of de Waal's (1982) Chimpanzee Politics, an account of the complex and dynamic power struggles amongst shifting alliances in a colony of chimpanzees, our closest living relatives. De Waal was often able to quote the advice given by Nicolo Machiavelli (1513) to the politicians (princes) of the day about how to subtly and skillfully manipulate one's social companions, because the advice matched up with the tactics of the chimpanzees. In adopting the tag of "Machiavellian Intelligence" we sought not to emphasize the nasty side of social scheming that is sometimes associated with Machiavelli's name in everyday language, but rather the fine adjustment of both competitive and cooperative maneuvers that Machiavelli explicated in his writings. This is the crucial link because although there is always a thread of competition attendant on living in any social group in the wild, in monkeys and apes this competition is subserved by the formation of alliances and coalitions, and these fluctuate in dynamic ways. Social skill in some thus creates pressure for greater skill in others, in a potentially spiraling "arms race." Humphrey compared primate social life to something like a game of chess, in which one's gambits were always played out in a social arena where the other players are constantly reactive and responsive, creating a moving landscape in which nimble social tactics are constantly selected for.

Whiten and Byrne (1988a) pointed out that, in fact, three different manifestations or levels of the social or Machiavellian intellect hypothesis (MIH) should be distinguished. The most basic is simply the hypothesis that in contrast to much of the earlier work focused on intelligence engaged with the physical problems typically posed in the comparative psychologist's laboratory, primate intelligence is also much engaged with social life. This version of the hypothesis may seem elementary, but it has led to what are now decades of rich and fascinating research that explores and identifies the complexities of primate social cognition in both wild and captive primates (Seyfarth & Cheney, 2015a, 2015b). The second and more ambitious version of the hypothesis is the claim that intelligence has been molded and enhanced more by social life than by other challenges such as foraging and predator evasion. The third version goes further to propose that the very nature of intelligence has been shaped by these social forces, so that there are characteristics of the primate mind and brain specifically adapted for the application of intelligence to the social realm. What Humphrey called "natural psychology," nowadays referred to by terms like Theory of Mind or mindreading, would be one such phenomenon (discussed later, under the heading "Mentalizing"), evolving as an adaptation to deal specifically with one's social world.

To many primatologists who in their research on primate social life were daily impressed by its intricacies, hypotheses such as these had an immediate and inherent plausibility. Testing them rigorously is another matter. Interestingly, this challenge was first taken up, influentially, by a focus on the brain. Robin Dunbar (1995) examined the relationship between measures of a primate species' relative brain size - encephalization - and a simple index of social complexity, the typical size of social groups in that species, and found the positive relationship the social intellect hypothesis predicts, whereas ecological variables did not have the same predictive power. Dunbar later dubbed the neural version of the MIH highlighted by this discovery the Social Brain Hypothesis (Dunbar, 1998; but see also Brothers, 1990, for a pioneering, earlier exploration of the Social Brain). Among the principal merits of Dunbar's approach is that the variables involved - namely, group size and neural volumes - are much more amenable to straightforward measurement than concepts like either social complexity or the sophistication of social cognition; among its limitations, of course, is that for those principally interested in these latter phenomena, the variables subjected to test represent relatively simplistic, surrogate entities. Nevertheless, the basic tractability of the approach has allowed a plethora of...