Glowacki explored the conditions required for peace and argued that its preconditions arose only within the last 100,000 years. Glowacki's latter contention receives strong support from a majority of anthropologists, archaeologists, and paleoneurologists who contend that a cultural bloom took place associated with Homo sapiens more recently than 100,000 years ago. This cultural bloom included depictive cave paintings, highly ritualized burials, personal ornaments, and long-distance trading for mates and resources (e.g., Coolidge & Wynn, Reference Coolidge and Wynn2018; Mithen, Reference Mithen1996). However, what has been neglected in his article is any mention of brain shape changes in H. sapiens within that time period and its likely cognitive sequelae for his “preconditions” and the cultural bloom. There is no mention in his text of the words “brain,” “cortex,” or “cognitive” that might be associated with those aforementioned archaeological aspects of modernity. It is the purpose of this commentary to address these lacunae. Specifically, I hypothesize that the well-documented expansion of the parietal lobes only in H. sapiens (but not in our extinct and close genetic cousins, the Neanderthals) in the last 100,000 years (e.g., Bruner, Reference Bruner2004, Reference Bruner2018; Pereira-Pedro, Bruner, Gunz, & Neubauer, Reference Pereira-Pedro, Bruner, Gunz and Neubauer2020) may account for one critical component of conducting peaceful negotiations in proximal and distal trading, that is, diplomacy. It is also important to note that this superior parietal lobe expansion was accompanied by inferior parietal lobe displacement into the superior and posterior portions of the temporal lobes, known for their critical role in language comprehension and inner speech (e.g., Aboitiz, Reference Aboitiz2017; Coolidge, Reference Coolidge2020).

The parietal lobes have a long- and well-established role in somatosensory functions, particularly visual and spatial processing, and the latter appears to be its original adaptive value in the evolutionary lineage of complex animal life, perhaps as early as 500 to 400 million years ago. This important role of the parietal lobes was especially critical in the origin of the primate lineage, beginning about 60 million years ago. These earliest primates (with whom we had a common ancestor) were small, socially gregarious, and were well adapted to arboreal life. Their arboreal niche required accurate placement of limbs navigating through branches and trees, a major function of the parietal lobes. The parietal lobes were also required for the learning and recall of locations and the integration between spatial references, specifically the translation and mediation between egocentric (self-centered or “own-eyes”) and allocentric (environmental, nonself, observer-like) perceptions (e.g., Mitchell, Czajkowski, Zhang, Jeffery, & Nelson, Reference Mitchell, Czajkowski, Zhang, Jeffery and Nelson2018). I have presented arguments elsewhere (e.g., Coolidge, Reference Coolidge2014, Reference Coolidge and Bruner2023), as have others, that the parietal lobes may have been exapted (a change in the original function of a trait for a new purpose) for roles in numerosity (appreciation of numbers; e.g., Dehaene, Reference Dehaene2011), the consolidation and recall of episodic (e.g., Allen & Fortin, Reference Allen and Fortin2013; Trimble & Cavanna, Reference Trimble, Cavanna, Dere, Easton, Nadel and Huston2008) and autobiographic memories (e.g., Tulving, Reference Tulving2002), and in constructive future simulations (e.g., Baddeley, Reference Baddeley2012; Schacter & Addis, Reference Schacter, Addis and Abraham2020). However, I wish to emphasize the critical exaptive role of an inferior portion of the parietal lobes that may have played in the ability to conduct diplomatic negotiations and that is the retrosplenial cortex (RSC).

The corpus callosum, which transmits information between the two cerebral hemispheres is covered by the cingulate cortex. The posterior part of the cingulate cortex is the RSC, which is already well documented for its role throughout evolution in spatial navigation and in mediating and translating between egocentric and allocentric perceptions (e.g., Vann, Aggleton, & Maguire, Reference Vann, Aggleton and Maguire2009). I hypothesize that the adaptive functions of the RSC have been exapted to conduct successful diplomatic negotiations in more recent H. sapiens.

When one crosses even relatively short distances in Europe, India, or other regions in the world, a bewildering variety of languages is encountered, a condition undoubtedly similar to the later Middle Paleolithic and Upper Paleolithic periods (75,000 to 30,000 years ago) when fully modern H. sapiens' brains and minds were in place and manifested themselves archaeologically by some of the aforementioned characteristics of modernity, particularly long-distance trading. There is archaeological evidence that these early H. sapiens were trading over 1,000 km (600+ miles), which strongly implies that a lingua franca was unlikely. Further, natural tendencies of xenophobia and other anxieties associated with dealing with strangers had to be overcome. Webb, Schweiger Gallo, Miles, Gollwitzer, and Sheeran (Reference Webb, Schweiger Gallo, Miles, Gollwitzer and Sheeran2012) empirically demonstrated effective emotional regulation requires identifying a need for emotional regulation in particular situations and enacting appropriate regulation strategies. Interestingly, they found that forming implementation intentions, specifically “if-then” planning, was significantly better (with a large effect size) at regulating one's emotions compared no regulation instructions. More recently, King, Romero, Schacter, and St. Jacques (Reference King, Romero, Schacter and St. Jacques2022) determined the powerful influence of shifting from egocentric to allocentric perceptions upon autobiographical memories, that is, personal events recalled like movie clips coupled with semantic (script or word-like) details. In their empirical study, they found that shifting to allocentric perceptions of episodic memories reduced the emotional intensity of subsequent recall with no loss of semantic information.

The Webb et al. (Reference Webb, Schweiger Gallo, Miles, Gollwitzer and Sheeran2012) and King et al. (Reference King, Romero, Schacter and St. Jacques2022) studies support our (Coolidge & Wynn, Reference Coolidge, Wynn, Gibson and Tallerman2012) earlier speculations about some of the cognitive prerequisites (nonorthogonal) for diplomacy, which includes adequate phonological storage capacity working memory to form complex thoughts, recursive thinking (e.g., “if-then” or “what-if” contingencies), and higher levels of theory of mind (the accurate reading of the thoughts, intentions, and attitudes or others). Thus, the gist of the present argument about the evolution of peace in the last 100,000 years rests on the dramatic neurological changes in the brain (specifically the RSC) and its consequential cognitive sequelae within that same period, which allowed for diplomatic negotiations, which in turn is an essential element of peace. By being able to regulate human emotions (like xenophobia), particularly because of its ability to translate between egocentric (how I feel) and allocentric (how they might feel) perceptions, fully modern H. sapiens were able to flourish after their entry into Europe about 50,000 years ago and then become the only surviving species of human primates.