Brain Building

The human brain is immense. Composed of 100 billion neurons with vast numbers of interconnections between them, it is no wonder that definitive statements are few and far between as to the overall operation of our brain. A useful simplification is to observe how the brain has grown and its abilities changed across the span of living organisms.

Tree of Life. Humans in a little, upper left. Mammals and the split from reptiles below

The Tree of Life

Nature Abhors Waste

For all creatures, a constraining force affecting genetic change can be summarized as nature abhors waste. New species, adapting to new environmental niches, are built upon whatever worked in the parent species, not from scratch. Instead of an eye with no predecessors, descendant species have an improved eye. The genetic inheritance of a new species contains incremental accretions on the founding genetics rather than wholly new genetic solutions.

Biological Decision Hierarchy. Simplest to Most Complex Response

Biological Decision Hierarchy. Simplest to Most Complex Response


Through the Eons

Evolution is the response to environmental challenges. Once a niche is saturated, variants of the organisms compete to open new niches. Genetics is the hardened, but generic solution to flourishing in environmental niches and yet is flexible enough to adapt to new opportunities.

Life has three useful separation points from the Mental Construction viewpoint.

  • Vertebrate. From simple amoebae immediately responding to touch sensation up to multi-celled organisms which have neurons, in localized nodes near their sensors and reactive cells
  • Reptile. With a central brain allowing for processing of all sensory information at one place. Reptilian brains perform some integration of senses before response, weighing the importance of the various sensory input. Thus the reptile’s response is more flexible than a fixed action.
  • Mammal. With a central brain for sensory processing covered by a cortex dedicated to integrating the senses with memory. The limbic system retains the ability to prioritize raw sensory inputs according to needs of the individual mammal. From whatever cause, mammals are known to be social creatures which adds demands upon the brain apparatus to support identification of others in the social group as well as tracking group activities.

The Adult Human Brain

Since Mental Construction’s focus is human cognition, details that are ignored in the broad brush of the mammals demand further analysis.

Of course, genetics lays the basic ground rules for humans, both in thinking and in expression. However language and society’s rules are learned incrementally. Critical learning periods leave marks at various depths in our mental structures.

In humans, in addition to the genetic imperatives of our heritage which play out, we add societal and linguistic organizations which mold our perceptions into settled categories and constrain our behaviors into approved norms.

As life developed from single-celled organisms, we can do no better than start there.

Amoeba. Stimulus - Response

Amoeba. Stimulus – Response

Brain through the Ages

Two people talking, thinking with language

Thinking with Language

Development to Adult Human Brain