Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
Multiple brains: the Advent of Cognition
Because higher functions of the brain tend to be generated by the regions (such as the cortex) that appeared in more recent species (such as us), it is likely that the human brain has accumulated functions and structures over the ages. Hughlings Jackson also noticed that a loss of brain function is often compensated by a gain in another brain function, and concluded that an evolutionarily “older” brain takes over whenever the “newer” brain is disabled: the older brain is still there, even though a newer brain grew on top of it.
Today's brain basically "summarizes" its evolutionary history: its structure and functioning contain its predecessors.
Older creatures tend to have no central nervous system, but rather a loose affiliation of nerve fibers. As we move down the genealogical tree, that chaotic form of communication among cells gets disciplined through a more and more centralized system that performs more and more sophisticated processing of the signals. Hot-blooded animals also need to control temperature and require a more complex control mechanism. Earlier mammals exhibit a forebrain and later mammals developed the cerebral hemispheres. Throughout this evolution of more and more refined nervous systems, the earlier ones remained around. The primitive forebrain is still part of the human brain (and it accounts for a lot of our emotional life). Loose networks of nerve fibers still control organs around the body, and often the brain cannot override them. And so forth. One can recognize within the human brain the facsimile brains of amoebas, insects, worms, etc.
The US biologist Philip Lieberman proposed that the brain consists of a set of specialized circuits that evolved independently at different times. Many specialized units work together in different circuits (the same unit can work in many circuits). The overall circuitry reflects the evolutionary history of the brain, with units that adapted to serve a different purpose from their original one. For example, rapid vocal communication (as in “speaking) is actually responsible for the evolution of the human brain, and not the other way around.
Lieberman's "circuit model" was derived from the model of the brain worked out by the US physician Norman Geschwind (“Disconnexion Syndromes In Animals And Man”, 1965, the manifesto of behavioral neurology) in order to explain aphasia, a model that reconciled localization and connectionism.
Besides language, another unique trait of the human race (and therefore of the human brain) is the moral code, in particular altruism. This would also be a relatively recent development, and presupposes circuitry for language and cognition.
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