Evolution's First Philosopher: John Dewey and the Continuity of Nature

4. Brain Development and the Emergence of the Mind

The world becomes full of organisms that have what it takes to become ancestors. That, in a sentence, is Darwinism. —Richard Dawkins, River out of Eden (1995:2) 찞 Studies of the human brain reveal a remarkable plasticity to develop biological tissue while at the same time leaving open the possibilities that postnatal survival might require major changes in the initial constructions. We will consider the basic biology and then examine, albeit briefly, how brains become minds. Dawkins’ idea of memes is introduced along with Dennett’s explanation of how brains evolved. Readers who do not want to review brain science nevertheless may be interested in Dennett’s serial-computer theory of mind. Readers familiar with Dennett’s writings may want to skip over this chapter. THE TRIUNE VIEW OF THE BRAIN One wonders whether the limbic system would ever have become such a “solar plexus” with respect to emotional feelings if it had not been for the development in mammals of the family unit dependent upon the nursing mother. —Paul MacLean (1985:220) 53 FOUR Brain Development and the Emergence of Mind PAUL MACLEAN’S BOOK Triune Brain in Evolution sets out a theory that the human brain can profitably be seen as having three basic parts that are distinguished on the basis of the brain’s evolution (McLean, 1991). If we think of the spinal cord as a walking stick, the earliest brain may be envisioned as the silver or brass knob on the end of the walking stick. This earliest brain is typically referred to as the “reptilian brain” (or the R-brain) and is also know as the archipallium (archi “first or basic,” and pallium “brain”). The R-brain form is at least 200 million years old (Hart 1983:36), and controls the autonomic nervous system, as well as decisions, among other things, about whether to fight or take flight. If you were to view the skull of an alligator or other reptile, you would notice that the brain case is very small. Zoologists will be quick to point out that the reptiles have all the brain they require to live their life style. The second brain identified by the triune theory is the middle brain, also known as the paleomammalian (paleo “old,” mammalian “mammal”) brain, which is 60 million years old (Hart 1983:36). McLean (1991) refers to the middle brain as the “limbic system,” which includes the amygdala, hippocampus , and hypothalamus. It is believed that the limbic system is responsible for our feelings of hunger and thirst and controls our emotional states. Continuing with the walking-stick analogy, imagine that the silver knob is covered with foam padding several inches thick. This paleomammalian brain is roughly sixteen times as large by volume as the R-brain. The third brain of the triune theory is the large human brain, the neocortex, or the neomammalian brain, and is only a few million years old. It is this neocortex that is divided into the much talked about left and right hemispheres that are connected by a bridge between the two, the corpus callosum. The corpus callosum is wider in women than in men, a fact that has led many to wonder if it could form the basis of the differences in observed behavior in men and women. A pattern we see used over and over again by evolution is the using of older structures in new ways. Brain studies show us that nature, by adding on to the old and/or putting it to work in new ways, has produced evolutionarily different forms. For example, we still retain the flight or fight interpretation of situations in which we find ourselves, but with the added computing power of the neocortex, we are able to better manage our more basic flight or fight impulses. We have all been in situations where we imagine throwing a book, or even a brick, at someone; but our higher executive function—our logical reasoning—found in our new, human brain inhibits this lower level urge. THE BRAIN AND INFORMATION PROCESSING [T]he microprocess by which a given neuron’s activation level is conducted across any synaptic gap, in order to stimulate or inhibit THEORY OF EVOLUTION 54 its target neuron at the next population, is a microprocess that is biochemical through and through. —Paul Churchland (1995:169) To gain some understanding of how the brain processes information, we should review the form...