Did the larger brain lead to the behaviors, or did the behaviors lead to the larger brain? If other evolutionary trends have relevance, they mutually reinforced each other and provided positive feedbacks; down one evolutionary line it reached conditions that led to the human brain. The initial behavior was probably the use of a body part (the brain) for a new purpose, and its success led to selective advantages that led to mutual reinforcement. Although it is by no means an unorthodox understanding, I think that the likely chain of events was walking upright freed hands for new behaviors, which led to new ways of making and using tools, which enhanced food acquisition activities. This allowed the energy-demanding brain to expand, as well as related biological changes, which led to more complex tools and behaviors that acquired and even more energy. That, in short, defines the human journey to this day, which the rest of this essay will explore. There has never been and probably never will again be an energy-devouring animal like humanity on Earth, unless it is a human-line descendant.
For all of their seeming cunning and behaviors right out of , rhesus monkeys cannot pass the ; they attack their images, as they see themselves as just another rival monkey. Chimpanzees, on the other hand, pass the mirror test, and the threshold of sentience, whatever sentience really is, may not be far removed from the ability to pass the mirror test, or perhaps humanity has not yet achieved it. , considered the most intelligent New World monkeys, have socially based learning, in which the young watch and imitate their elders. Different capuchin societies have different cultures and different tool-using behaviors reflected in different solutions to similar foraging problems. Capuchins, isolated from African and Asian monkeys for about 30 million years, have striking similarities to their Old World counterparts, with female-centric societies and lethal hierarchical politics. As with chimpanzees and humans, ganging up on lone victims is the preferred method, which increases the chance of success and reduces the risk to the murderers. Unlike rhesus monkeys, for instance, capuchin males can help with infant rearing, but they will also kill infants that they did not father, as rhesus, also do (that behavior has been observed in 50 primate species). Those comparisons provide evidence that simian social organization results from the connection between simian biology and environment; their societies formed to solve the problems of feeding, safety, and reproduction.
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has been a prominent hypothesis that posited that behaviorally modern humans suddenly appeared. It was once considered an abrupt event that began about 50-40 kya, but as new archeological finds are amassed, as well as recent advances in genetic research and other areas, the story is familiar. Although on the geological timescale the event was abrupt, radical, and unprecedented in life’s history on Earth, the “ramping” period seems to have lasted longer than initially thought. A likelier story is that in East Africa, which conforms to a . inherited culture and tools from their ancestors and continued along the path of inventing more complex technologies and techniques, exploiting new biomes, and reaching new levels of cognition. There does not seem to be any or development that needs to invoke divine or extraterrestrial intervention to explain the appearance and rise of . Some migrated past their African homeland during the of 130 kya to 114 kya and brought along their technology. Although they may have disappeared and perhaps became Neanderthal prey, vestiges of their fate are probably yet to be discovered. They may have contributed to the biological and technological wealth of Eurasian humans and may have begun to drive vulnerable species to extinction with their new tools and techniques. However, Africa remained the crucible of primate biological and technological innovation, as it almost always had to that time. By 70-60 kya, isolated African humans reached a level of sophistication called behavioral modernity. Art was in evidence, needles made clothes and other sophisticated possessions, and they mastered language, which was probably a unique trait among land animals. They made tools of a sophistication far advanced over other humans, which probably included projectile weapons that radically changed the terms of engagement with prey animals, predators, and other humans.