Beginning with the single-celled eukaryote:
the cell structure of membrane “skin” and
its attachments and ports (ion gates, cilia for movement),
the structure of the interior,
the nature and number of inclusions, “captured” sub-cells,
capacity to create molecules,
ability to detect and use motion to approach food and
move away from danger,
move away from danger,
ability to exchange genetic material with other cells through
Collaboration with other cells:
Formation of localized structures that specialize in breathing, heart beat regulation, balance, basic motor movements and foraging skills.
These structures become more sophisticated over time. Newer structures usually form around the older parts rather than discarding them.
The primitive hind brain (the protoreptilian brain) forms to sustain fundamental homeostatic functions. Includes the pons which is considered part of the brainstem. It transmits messages and is the origin point of dreams. The medulla — sometimes called Medulla Oblongata — is involuntary and entirely unconscious but crucial to life as it regulates blood pressure and breathing. It helps transfer neural messages from the brain to the spinal cord through the vagus nerve and the autonomic nervous system. The reticular formation is a set of interconnected nuclei (clusters) that are located throughout the brain stem.
Arrangements tend to be cumulative from the brainstem at the top of the spinal column forward to the front, but not always, as new additions sometimes require more space and develop in a way that pushes things around.
The cerebrum and cerebellum have a different structure in that they are arranged into cortical architecture, layers with the white (insulated) axons underneath the gray matter. It is convoluted, as they say, like a dinner napkin crumpled into a wineglass.
The cerebellum is behind the brainstem and below the occipital lobe of the cerebrum in humans. It’s interior axon fiber tracts are called the arbor vitae or Tree of Life. In reptiles and fish it was the pallium before part of it elaborated as follows: “In mammals, the cortical part of the pallium registers a definite evolutionary step-up in complexity, forming the cerebral cortex, most of which consists of a progressively expanded six-layered portion isocortex, with simpler three-layered cortical regions allocortex at the margins. The allocortex subdivides into hippocampal allocortex, medially, and olfactory allocortex, laterally (including rostrally the olfactory bulb and anterior olfactory areas).”
Differences in total size were disproven as signalling improvement or uniqueness. (Men have bigger brains, but that doesn't mean smarter.) This is a quote: “Different sizes in the corticol areas can show specific adaptations, functional specializations and evolutionary events that were changes in how the hominoid brain is organized. In early prediction it was thought that the frontal lobe, a large part of the brain that is generally devoted to behavior and social interaction, was the main player in the differences of behavior in hominoid and humans. This theory was dispelled by the test that showed that with damage to the frontal lobe both humans and homonoids [chimps] show atypical social and emotional behavior meaning that the frontal lobe was not very likely to be selected for reorganization. Instead, it is now believed that other parts of the brain that are strictly associated with certain behaviors was where evolution targeted. The reorganization that took place is thought to have been more organizational than volumetric; whereas the brain volumes were relatively the same but specific landmark position of surface anatomical features, for example, the lunate sulcus suggest that the brains had been through a neurological reorganization.
“There is also evidence that the early hominin lineage also underwent a quiescent period, which supports the idea of neural reorganization.” This quiescent period is analogous to the “adrenarche” or even earlier time before the adult teeth grow in. Some call it “middle childhood.” This is the time of learning social structure, developing culture and identity, and developing speech. These are thought to be the factors that make humans more “fitting” because it is a time of “plasticity” for individuals, a crucial quality of humans who can adapt to a wide range of circumstances.
Evolution of the genetic blueprint
“Two genes were found to control the size of the human brain as it develops. These genes are Microcephalin and Abnormal Spindle-like Microcephaly (ASPM). The researchers at the University of Chicago were able to determine that under the pressures of selection, both of these genes showed significant DNA sequence changes.”
The Rest of the Body
Clearly, where ever neurons go is a part of the brain, not just accumulating data, but sorting, editing, weighting, even making instant decisions like pulling back a burnt finger. Much of it is not accessible to consciousness, not even speechless concepts. But the gut, which has a LOT of neurons and all the organs that send and accept secretions as communication, are “thinking” as directed ultimately by the brain as dashboard.
Pressure from the environment forces adaptation
“The researchers statistically analyzed the key differences between the primate and human DNA to come to the conclusion, that the differences were due to natural selection. The changes in DNA sequences of these genes accumulated to bring about a competitive advantage and higher fitness that humans possess in relation to other primates. This comparative advantage is coupled with a larger brain size which ultimately allows the human mind to have a higher cognitive awareness.” (More storage.)
So much of our environment is human, pressing on us with violence, stigma, false notions, conditioning, habits, etc. that the brain must devote much more space to all this, esp. since we are living concentrated but imaginary media lives. There is evidence that individual spindle cells are developing sensitivity to all this, a big example being “mirror cells” which help us “see into” other people.
Natural random mutations are now interacting with human-built structures, economic resources, community requirements, and the natural geological and climatological changes of environments on the planet. These are pressing evolution in what is probably a mosaic pattern around the world: that is, some brains have hardly changed while others are processing and inventing quite differently. It’s hard to tell what will be an advantage without looking back over a life. Schizophrenia may turn out to be very helpful. Simple endurance may save people in the great wastes of famine. Machiavellian lack of conscience seems to be an advantage in crowded capitalistic settings. Evolution only responds to the actual, not the ideal.
Probably much more evolution than we are aware of is happening on the molecular level in food additives, herbicides, gender-related hormones, anti-depression drugs and so on. In fact, depression itself may be a result of environment pollution that we have created. But rumors that the government may require the removal of such drugs from sewage systems are frightening because they will be catastrophically expensive. The main evolution will be speedier destruction of small towns who can’t pay for such amelioration. And yet, we often think of small rural communities as places that can shape humans in good ways.
Barrels, stripes, and the septa that seperate them likely form as a result of conserved developmental mechanisms that depend on correlated neuronal activity from a sensory sheet to form connections within modules.