A brain that processes input but not output doesn’t help survival. To do that a brain must analyze receptor input and control effector output, as when the eyes see danger and muscles allow us to run away. The resulting basic feedback loop (Figure 6.19) is how the brain interacts with the environment to help us survive, but is this loop initiated by the brain or outside stimuli? What drives the basic feedback loop was the origin of a great debate in psychology last century.
Behaviorism argued that as people are machines driven by outside events, stimulus and response entirely define the loop and what the brain does. In contrast, constructivism argued that the brain controls the loop by actively constructing reality, hence we can produce more sentences than we could ever learn from stimulus-response associations (Chomsky, 2006).
The theories differed on what initiated the basic feedback loop, which was input-driven in behaviorism and brain-driven in constructivism (Figure 6.20. Since one can initiate a circular process at any point, today we accept that both can be true, as the brain can dream realities with no external basis or be driven by outside events. It could neither learn nor evolve if it couldn’t initiate the feedback loop.
A brain that evolves still has to run the feedback loop, but how it can evolve while operating? Microsoft computers at first had the DOS operating system until Windows replaced DOS, making it obsolete along with all the time users spent learning it. In this case, Windows overlaid DOS but if the mammal brain made the reptile brain obsolete, nature would be discarding hundreds of millions of years of evolution!
Nature doesn’t discard advances so an American neuro-physiologist at the National Institute of Mental Health argued that our brain is a reptile brain overlaid by a mammal brain overlaid by a human cortex (MacLean, 1990) (Figure 6.21), where the reptile brain uses hind brain structures like the cerebellum, the mammal brain uses the mid-brain limbic system and the human brain uses the neocortex to give higher thinking. He then explained autism as an out-of-control reptile brain and anxiety as an out-of-control mammal brain. In this view, evolution developed a reptile brain to handle movement, a mammal brain to handle emotions and finally created a neocortex for human thought, so our brain is three brains in one, each overlaying the last.
This brain model became popular as it explained autism and animals. Temple Grandin, an authority on animal psychology who is autistic, wrote:
“To understand why animals seem so different from normal human beings, yet so familiar at the same time, you need to know that the human brain is really three different brains, each one built on top of the previous at three different times in evolutionary history. And here’s the really interesting part: each one of those brains has its own kind of intelligence, its own sense of time and space, its own memory, and its own subjectivity. It’s almost as if we have three different identities inside our heads, not just one.”
The reception of the three-brain model among neuroscientists wasn’t nearly as positive because evolution doesn’t work by layering one new thing after another, like geology does. As one critic put it: Your brain isn’t an onion with a tiny reptile inside. Evolution didn’t build a reptile brain, then a mammal brain, then a human cortex because it isn’t a linear production line. Nor does it add new things with no precedent as bat wings are modified forelimbs that existed before. In biology, even reptiles have cortical analogues and can care for their young and solve problems (Patton, 2008).
Triune theory also didn’t account for birds. Over millions of years, reptiles evolved into dinosaurs whose ancestors today are birds. Birdbrain is a term of ridicule but they are quite smart, as crows can bend a wire into a hook to get food their beak can’t reach (Weir et al., 2002) (Figure 6.22). Children can’t use tools like this until about eight and even then, only half succeed (Cutting et al., 2014). Birds like nutcrackers can hide 30,000 seeds over a 200 square mile area and recover them six months later. Birds are more like feathered apes than reptiles and urban crows are especially smart:
“On a university campus in Japan, crows and humans line up patiently, waiting for the traffic to halt. When the lights change, the birds hop in front of the cars and place walnuts, which they picked from the adjoining trees, on the road. After the lights turn green again, the birds fly away and vehicles drive over the nuts, cracking them open. The birds wait patiently with human pedestrians for a red light before retrieving their prize. If the cars miss the nuts, the birds sometimes hop back and put them somewhere else on the road.” ()
It is generally accepted that birds share many cognitive abilities with advanced mammals but evolved different brains to do so (Jarvis & et al., 2005). If evolution was building a mammal brain, why also build a bird brain with equivalent abilities? The current view is that the evolution of bird and mammal brains converged to intellectual functions (Lefebvre et al., 2004) from the basic reptile design but the bird cortex is smooth while the mammal cortex is folded, so nature tried both options. Triune theory explains what other theories don’t but it doesn’t fit what we know about evolution. An alternative that does is now explored.