Our brain size increased as we migrated (1) and pair-bonded. (2) We developed the hypothalamus and the thalamus enabling us to deploy sensory and motor skills to interface successfully with our environment. We strengthened our ability to vocalize distress in response to the feeling of pain, which then was mediated by neurochemical opiates. (3)
These and similar processes specialized our neural networks (4) and introduced new forms of neurochemical signaling. (5) We “got smarter” because a huge number of cortical neurons enabled us to gather and process information quickly. Human intelligence is highly heritable, which augmented this increase in “raw processing power.” (6)
We learned how to manufacture and deploy efficient, high-quality tools. (7) We observed how rocks chip in a certain way, enabling us to exploit their physical properties such as material toughness and indent location. (8) Our ability to do so was facilitated by the specialized morphology of our wrists. (9) Acquiring these and other skills enhanced our cognitive capacity. (10)
The same “architectural constraints on brain evolution” abetted “niche-specific cognitive challenges.” (11) We were forced us to resolve “conflicts of interest” between parental genomes and conditions on the ground. For example the neurochemical serotonin affects our disposition for aggression, “startle response” and fear-processing mechanisms. (12) An individual’s “fight-or-flight” fear response “is good for individual or species survival because it allows individuals to confront or avoid threats.” The “production and suppression of fitness-related behaviors,” however, “potentially have divergent costs for parental genes.” Fearful offspring are more likely to reproduce whereas less fearful ones are more likely to get eaten. (13)
Serotonin also introduced neural and functional aspects of what we have come to call “pride” and “shame,” (14) with similar evolutionary consequences. Opiates facilitated pair-bonding and made us fall in love. (15)
Cellular biology, however, only is part of the story. The neurochemical changes taking place inside our brains augmented our material culture and social structures. (16) In order to deploy tools and engage in similar activities we also had to acquire “a species-specific set of social-cognitive skills” “for participating and exchanging knowledge in cultural groups.” (17)
Besides devising ingenious techniques to cope with our environment we devised practices to cope with each other. We overcame a kind of “complexity threshold” and developed reproductive effort, survival ability and colonization capacity. (18) We formed agglomerations or tribes of individuals. Our offspring were born into a hierarchy of reciprocally, mutually-interdependent relationships. (19) “[S]ocial behavior, tool-making, language, hunting” and other similar activities were “integrated in a developmental matrix.” (20)
Brain size and chemistry alone are “inadequate to explain” this “range of human behavioral flexibility.” (21) Consider for example the case of the whale. Humans have more cortical neurons than most other mammals although only marginally more than whales. Cetaceans are remarkably adapted to their environment. In Moby Dick (22) Melville made a good case that our “intelligence” is not “better,” just “different.” Whatever improvements we made over whales and other primates must have resulted from adding cultural factors rather than from “unique” features of our brains, alone. (23) Among these were “language, social intelligence, tool-making, and motor sequences.” “Environmental input, including self-generated input, interacts with mental constructional capacities to assure that developing humans acquire species-typical and culturally-specific behavioral patterns.” (24) The brain is only one component “of a larger set of coevolved traits.” Our “human adaptive complex” particularly includes the capacity to devise, implement and maintain community and social relationships. (25)
Neither brain development nor the emergence of culture occurred in a vaccum; both were necessary to achieve these outcomes. There is a back-and-forth relationship between cognitive evolution and social evolution. (26) Our “expanded human mental capacities primarily reflect the increased information processing capacities of the enlarged human brain including the enlarged neocortex, cerebellum, and basal ganglia.” These “increased information processing capacities,” however, were enhanced by our “human abilities to combine and recombine highly differentiated actions, perceptions, and concepts in order to construct larger, more complex, and highly variable behavioral units in a variety of behavioral domains.” (27)
This is how culture in its most nascent form began to emerge. “Transforming our understanding of life is the realization that evolution occurs not only among individuals within populations, but also through the integration of groups of preexisting individuals into a new higher-level individual, that is, through evolutionary transitions in individuality.” (28) “[L]ife has not evolved on a static planetary surface. Rather, life and environments have evolved together throughout our planet’s history.” (29) “[B]rain structures form a cultural neurohermeneutic system which functions like a bow firing arrows linking past and future realities. This system is a connector in human affairs and can explain everyday life.” It “functions as an interpretive hierarchy that permits individuals to make increasingly complex interpretations of social events.” (30)
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(3) Tucker, D., Luu, P., Derryberry, D., “Love hurts: The evolution of empathic concern through the encephalization of nociceptive capacity,” 17 Development and Psychopathology 699 (2005).
(4) Sperber, D., “In Defense of Massive Modularity,” in Dupoux, E. & Mehler, J. (eds.), Language, Brain and Cognitive Development: Essays in Honor of Jacques Mehler 47 (2001).
(5) Williams, R., “The biological chemistry of the brain and its possible evolution,” 356 Inorganica Chimica Acta 27 (2003).
(6) Miller, G. & Penke, L., “The evolution of human intelligence and the coefficient of additive genetic variance in human brain size,” 35 Intelligence 97 (2007).
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(8) Chai, H. & Lawn, B., “A universal relation for edge chipping from sharp contacts in brittle materials: A simple means of toughness evaluation,” 55 Acta Materialia 2555 (2007).
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(10) Marino, L., “Convergence of Complex Cognitive Abilities in Cetaceans and Primates, 59 Brain, Behavior and Evolution 21 (2002).
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(13) Brown, W., “Evolved Cognitive Architecture Mediating Fear: A Genomic Conflict Approach,” in Gower, P. (ed.), The Psychology of Fear 171 (2003).
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(15) Marazziti, D., “The Neurobiology of Love, 1 Current Psychiatry Reviews 331 (Nov. 2005).
(16) Donald, M., “The Central Role of Culture in Cognitive Evolution: A Reflection on the Myth of the “Isolated Mind,” in Nucci, L., Saxe, G. & Turiel, E. (eds.), Culture, Thought and Development (2000); Reader, S. & Laland, K., “Social intelligence, innovation, and enhanced brain size in primates,” 99 Proc. Nat’l Acad. Sci. 4436 (Apr. 2002); Mithen, S., “Mind, brain and material culture: an archaeological perspective,” in Carruthers, P. & Chamberlain A. (eds.) Evolution and the Human Mind – Modularity, language and meta-cognition 207 (2000); Castro, L. & Toro, M., “The evolution of culture: From primate social learning to human culture,” 101 Proc. Nat’l Acad. Sci. 10235 (Jul. 2004).
(17) Hermann, E., Call, J., Hernández-Lloreda, M., Hare, B. & Tomasello, M., “Humans Have Evolved Specialized Skills of Social Cognition: The Cultural Intelligence Hypothesis,” 317 Science 1360 (2007).
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(20) Holloway, R., “Culture, Symbols, and Human Evolution: A Synthesis,” 5 Dialectical Anthropology 287 (1981).
(21) Neill, D., “Cortical evolution and human behavior,” 74 Brain Res. Bull. 191 (2007).
(22) Melville, H., Moby Dick (1851).
(23) Roth, G. & Dicke, U., “Evolution of the brain and intelligence,” 9 Trends in Cognitive Sciences 250 (2005); Lynch, G. & Granger, R., Big Brain: The Origins and Future of Human Intelligence 7 (2009).
(24) Gibson, K., “Evolution of Human Intelligence: The Roles of Brain Size and Mental Construction,” 59 Brain, Behavior and Evolution 10 (2002).
(25) Kaplan, H., Gurven, M. & Lancaster, J., “Brain Evolution and the Human Adaptive Complex – An Ecological and Social Theory” in Gangestad, S. & Simpson, J. (eds.) The Evolution of Mind: Fundamental Questions and Controversies 28 (2007).
(26) Donald, M., “The Central Role of Culture in Cognitive Evolution: A Reflection on the Myth of the ‘Isolated Mind’,” in Nucci, L., Saxe, G. & Turiel, E. (eds.), Culture, Thought and Development 19 (2000).
(27) Roth, G. & Dicke, U., op. cit.
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(29) Knoll, A., Life on a Young Planet 23 (2004).
(30) Reyna, S., Connections: Mind, Brain and Culture in Social Anthropology 3 (2002).