Evolutionary biologists study the development of the human brain in relation to different types of animals to understand the evolutionary path that has led to its complexity. They believe that the human brain has evolved over millions of years, and its development can be compared to the brains of other animals to trace its evolutionary history. They argue Darwinian theories, including natural and sexual selection, to explain human characteristics as part of the evolutionary process. Essentially, these successful characteristics are adaptations forged through evolutionary processes to solve problems of our ancestral past.

Evolutionary biologists also concentrate on the specific brain regions and structures that have undergone the most significant changes during evolution. The development of the human brain from infancy to adulthood occurs in several distinct stages. During infancy, the brain undergoes rapid growth and development as neural connections are established and sensory experiences contribute to brain maturation. This period is crucial for laying the foundation for future cognitive and emotional development. As a child grows, the brain matures, and the prefrontal cortex, a key area associated with higher-order cognitive functions such as decision-making, reasoning, and impulse control, undergoes significant development during adolescence. The brain continues to refine its neural pathways and establish more efficient communication between different regions. The brain reaches its peak development level in adulthood, characterized by consolidating cognitive abilities and emotional regulation. While the brain's basic structure is established in childhood, it continues to undergo subtle changes and refinements throughout adulthood in response to learning, experiences, and environmental stimuli.

Why is sequential development required? According to Volkmann, the association areas are integrating everything that has come before. Like a self-modeling scaffold, the brain continually grows while changing and rearranging previously grown brain areas. More information cannot be appropriately integrated without basic foundational brain growth and development. Volkmann states that most sensory motor developments happen in early childhood, while most integration happens in adolescence. If we must summarize each plane of development in one word, the first plane is sensory, the second is reason, the third is society, and the fourth is humanity. The brain has remarkable plasticity, but it is dependent on experiences. Experiences strengthen those connections stimulated by the experience as the brain prunes away unnecessary connections that never received the stimulation necessary to keep them around. Our brain's plasticity may also contribute to a human's unique susceptibility to neurodegenerative diseases.

Scientists have proposed reasons for why the brain takes so long to develop. Some believe this late development properly allows for integration instead of relying on preprogrammed, built-in instinctual information. With delayed brain development, we can learn from our own experiences and those of others. Learning through experience may also suggest that humans are programmable, as evidenced by our different languages and cultures. Humans initially have the capacity to speak any and all human languages, but through the environment, they are molded to reflect the society they live in as a whole. This adaptability of the human brain, shaped by the environment, is necessary for larger societies to work together cohesively. The answer could be far more straightforward. For a human to give birth without permanent injury or death, there is only so much head circumference that can be withstood. Proportionally, to other animals, we have giant heads and brains, but being too big means that there would not be any successful births. The limitations of the birthing process could set the size of the human brain at birth, but later growth and development allow for continued learning and intelligence.

However, new research from Dr. Aida Gomez-Robles (UCL Anthropology and Genetics, Evolution & Environment) found “that humans are born with brains at a development level that's typical for similar primate species, but the human brains grow so much larger and more complex than other species after birth, it gives a false impression that human newborns are underdeveloped, or "altricial." She also said, “Humans seem so much more helpless when they're young compared to other primates, not because their brains are comparatively underdeveloped but because they still have much further to go." This new research shows that this measure is misleading as other measurements of human brain development show humans are largely in line with other species of primates.

If humans and other primates have more in common than we thought, why is there such a cognitive rift? Marc Hauser, professor of psychology, biological anthropology, and organismic and evolutionary biology in Harvard's Faculty of Arts and Sciences, “presents four distinguishing ingredients of human cognition and shows how these capacities make human thought unique. These four novel components of human thought are the ability to combine and recombine different types of information and knowledge in order to gain new understanding, to apply the same "rule" or solution to one problem to a different and new situation, to create and easily understand symbolic representations of computation and sensory input; and to detach modes of thought from raw sensory and perceptual input." He summarized this with a metaphor that animals have laser-beam focus while humans have flood-light focus.

Dr Fernando Rosas suggests the rift is caused by humans’ ability to use synthesis processing versus redundancy. Redundancy means there are similar functions in different parts of the brain, while synthesis means different parts of the brain work together, which makes the computing power of the whole greater than the sum of its parts. Some believed humans had more neurons than other animals, especially in the cerebral cortex. Still, Suzana Herculano-Houzel, a neuroscientist at the Institute of Biomedical Science in Rio de Janeiro, demonstrated that humans have a similar number and proportion of neurons to other animals. “She argues that the human brain is actually just a linearly scaled-up primate brain that grew in size as we started to consume more calories, thanks to the advent of cooked food.” However, a recent discovery by neuroscientists from MIT found that human neurons have fewer ion channels than other animals, which essentially is an energy-saving hack that would allow for that energy to be utilized in other facets like neuronal or circuit processors.

Suppose we were looking at this through the Nature Vs. Nurture debate of what makes a human, we have covered many topics concerning the nature argument. However, we cannot discount the importance of the nurture component, which is precisely what sociobiologists investigate. Sociobiology looks at the variability of human behavior due to the interaction of universal evolved psychological mechanisms with variable environments. This universal core set of psychological mechanisms is what we call "human nature." These evolved psychological mechanisms are information-processing circuits responsible for collecting information and creating functional outputs for problem-solving. Domain specificity explains how specific adaptative problems are best solved by specific adaptation solutions. Ultimately, our evolved psychological mechanisms would be a product of past selective forces.

Where does personality come from? According to George Herbert Mead’s theory of social behaviorism, he stated social experience develops an individual’s personality. The “self” is the part of an individual’s personality made from self-awareness and self-image. Charles Horton Cooley created the concept of the “Looking Glass-Self,” which states a person’s self grows out of society’s interpersonal interactions and perceptions of others. This leads people to reinforce other people’s perspectives on themselves. For Mead, the self comes from social communication, which is the basis of socialization.

Socialization prepares people to participate in a social group by teaching norms and expectations. It is the process of transferring norms, values, beliefs, and behaviors to future groups. Socialization is culturally specific; one is not better than the other. In "Broad and Narrow Socialization (1995)," Jeffrey J. Arnett outlined the three goals of socialization: Impulse control and conscientiousness, preparation for social roles, and cultivating shared sources of meaning and value. Sociobiologists believe that inherited behavioral mechanisms can allow an organism a greater chance of surviving and reproducing. Observing socially deprived humans has highlighted critical periods of needed environmental stimuli for proper development. Recorded cases of feral children demonstrated a failure to develop language and limited social understanding, and the patients could not be rehabilitated. The critical period hypothesis points to the critical role of socialization in overall human development. It’s safe to say that the trajectory of brain development from infancy to adulthood is influenced by a combination of genetic factors, environmental influences, and individual experiences, all of which contribute to the complex process of brain maturation and refinement.

Some scientists view child development as a recapitulation of human evolution. This concept, known as "ontogeny recapitulates phylogeny," suggests that the stages of individual human development mirror the evolutionary history of the human species. This was one of Hall’s main points in his book “Adolescence.” He stated that child and human development mirrors human evolution, specifically the development of the brain. For example, the rapid growth and development of the brain during infancy parallels the early stages of human evolution when the brain underwent significant changes and expansion. The regions of the brain that grow during infancy and childhood are nearly identical between humans and other apes. High-growth areas include centers for language development and reasoning. Similarly, the maturation of cognitive functions such as decision-making and impulse control during adolescence mirrors the development of these traits in humans' evolutionary history.

I believe that the evolution of early humans also recapitulates Dr. Montessori's Planes of Development. The defining characteristics of a plane match well with the defining advancements of particular early humans. The sequential order between the Planes of Development and early human development matches so well that it couldn't be a coincidence. This means that as we watch our children grow from infancy to adulthood, it is like watching a movie about the evolution of humanity throughout a human lifetime. Each sensitive period and important developmental landmark we fawn over were crucial developments in the evolution of humanity. This also provides hope for the future because if human evolution follows the planes of development, at some points, our primary concerns as a species will be responsibility and purpose, finding balance in our adult lives, and establishing a role within our community. With advancements in AI, there is a promise that lots of work will become automated. However, we know humans find purpose in work, so the new work may strive for self-realization.

Refer to the image gallery to see how Montessori's Planes of Development match early human evolution.

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