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But brains do not just evaluate responses. They gather information. Without visual or audio inputs information gathering and sentient response are not so different. But over evolutionary time pleasure of light and fear or elation at movement produced a new form of sensation. This occurs when light and movement awareness produces sensation as information only, without direct motive of "pain" or "pleasure". This higher form of awareness manifested as vision, and later hearing, allows the development of consciousness. This is awareness of the world in a more orderly form. Once evolved visual or audio consciousness allows organisms to register sensations that inform rather than compel. Movement of a large animal might compel flight as reflex, but with consciousness an organism can evaluate if this particular situation does require flight, or if it is safe to stay and gather more food. This will increase options of when to rest or expend energy, and increases behavioral opportunities.

Yet for all the advantages both sentience and consciousness offer, nature never abandons the non-sentient autonomic response system. Instead, in the design of any brain (including hominid brains - see diagram) evolution builds layers of sentient response on top of the non-sentient system, such that organisms with consciousness experience two forms of response. One is the primal, autonomic muscle twitch response independent of sensation. The other is the sentient response, in which motor neurons, rather than responding with a muscle twitch, produce sensation, which by its power motivates the organism to move the muscles it consciously controls in certain behaviors.

In medical terminology any effect producing a response in an organism is called a stimulus, while the process of stimulus-response, without the intermediary of sensation is called reflex. But in philosophy stimulus refers to effects producing sensation, while either sentient or non-sentient responses, providing they are automatic are lumped together as reflex. The distinction is important for the next stage of evolution, which not all brains achieve; evolution of mind. Mind occurs when a brain can experience sensation without direct stimulus. In any brain all sensations, even those from stimulus, are only the body's biochemistry acting on consciousness. But as organisms become more complex nature utilizes the body's biochemistry to create new sensations acting on sentience as mood, affection or emotion, but without direct stimulation. The affection "fear" say, is an abstraction of the sensation "pain", so that a higher organism can experience fear, without direct stimulation of pain. The evolutionary advantage to this is that "fear" will motivate an organism to avoid situations causing "pain", plus emotions help organisms evaluate complex situations where direct stimulus might provide conflicting signals, such as sighting food and danger together. Emotions like fear play a further reflexive role such as heightening the body's preparedness to deal with danger by pumping adrenaline into the blood stream.

Finally, while we regard consciousness as being in a state of awareness when awake, sensation without stimulation, as occurs in mind, can produce mental processes when the brain is asleep, or unconscious. Because all higher mammals dream, learn, remember, and experience emotion, they possess mind, though critics might argue that only humans truly possess mind in its connoted sense. Just we should not become mystical over the meaning of mind. Anatomically it is another layer of neurology built up over the more primitive brain layers. So there are several layers altogether. There is the non-sentient autonomic system, the sentient response system, visual, audio and information gathering response systems, and finally, the topmost layer composes the more complex circuits of mind.

Yet, if mind is so important that only some brains evolve it, what is the enabling technology that makes mind possible?

It is those attributes referred to in this book as learning circuits, and is very important. The first neural circuits to evolve are for reflex, which we say has a fixed wiring diagram. Wiring is a poor term in that it is more like tubing than wiring, but bear with the metaphor. These fixed, reflexive neural circuits are ones in which axons connect to neurons in specific patterns encoded in the genes. Thus, the connection pattern was developed slowly by evolutionary selection of winning designs. (See diagram of typical reflexive circuits.) On the other hand learning circuits are not coded hardwired. Instead, much of the connection is made after birth. The genes encode messages not of how to wire circuits to a specific pattern, but instructions about how to wire up, test, and modify a neural circuit on the fly depending on stimulus. The evolutionary advantage of this is that whereas a thousand distinct reflex circuits would require a thousand separate instructions of how to wire them, a leaning circuit would only require one instruction how to wire it, and another instruction of say, how to reproduce this one pattern many times.

In this sense, learning circuits solve two evolutionary problems at once.

They allow a much more flexible neurology allowing customization to circumstance, the way modern software can be customized to specific needs.

Despite producing a more complex brain, learning circuits limit the number of genetic instructions that must be passed on to design a brain. This becomes crucial as the "bits" of complexity needed for brains exceed the "bits" of information which can be reasonably encoded in genes.

This problem of number of instructions is illustrated in the graph attached. This hypothesis was popularized by Carl Sagan in the "Dragons of Eden", but Sagan never followed his argument through. The estimated crossover point is 3 billion bits of information, which can be transmitted by genes, the amount of information a reptile needs in its brain. Mammals radiated 65 million years ago with a more complex, energetic brain than available to reptiles, requiring about 100 billion bits of information for a small mammalian brain. So, 65 million years ago evolutionary niches of creatures who could survive with a brain whose neural circuits could be completely specified genetically were already filled. With genetic code already saturated with instructions of how to wire a brain, nature began selecting for creatures that could multiply their most versatile reflex circuit many times. After this creatures using learning multiplied.

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