Nature versus nurture


Much of modern psychological thought appears to be based on another well-traveled myth: that the brain is a “blank slate” at birth–that what we become depends almost solely on our environmental experiences. So psychologists and psychiatrists¬†tend to be programmed to find “causes” for so-called psychiatric conditions and disorders in past emotional experiences and “learned” behaviors. The problem is, many such conditions and disorders have much more to do with our genes than our circumstances. Generally, a genetic imperative will be expressed in one fashion or another. Environment can help shape the expression of some genetic characteristics.

For example, a study by Pincus of violent individuals (murderers) found it took three factors occurring together to produce most such individuals: having been abused as a child (environment), frontal lobe brain dysfunction/damage (biologic/genetic), and paranoia (biologic/genetic–as in schizophrenia). Any single factor alone was usually not sufficient.19

Some traumatic environmental experiences (e.g., chronic childhood physical or sexual abuse) may be associated with changes in the brain that can cause impairment, including a smaller hippocampus.20

Certainly, some parts of the brain are “blank” at birth so that much of what we experience and learn can be encoded–that’s necessary for survival. Our experiences certainly do help shape us. But lying firmly beneath the mantle of environmental experience is our inborn self, our primarily pre-wired self. An analogy might be a tree. The roots and trunk and main branches make up our genetic, inborn self, while the smaller branches and leaves that sway in the wind make up our environmentally influenced self.

An example: You might have an interest in learning about a particular topic. The act of learning about it would be primarily environmental. Having an interest in it–being drawn to it–would be primarily inborn. And, of course, how well and how quickly you can learn is primarily inborn.

Note that inborn comprises both genetics and the pre-birth fetal environment.

We walk in the shadows of our evolutionary ancestors. As the brain developed down through evolutionary eons, it did not discard its older parts, but added on to them in a piggyback fashion. Because of this process, the old brain talks to the new brain (cortex). We remain captives in a sense to the primal drumbeats our distant ancestors instinctively marched to as a matter of survival. We are still nudged by a primitive “fight or flight” system. Thus, the “free” choices our cortex makes are in large measure influenced–automatically and involuntarily–by the inborn ancient drumbeats from subcortical sites. One of these subcortical sites is the limbic system, which may be the site controlling the level of excitation feedback, one of the two components in my model of stuttering. How excitation feedback can explain stuttering’s Primary Paradox is looked at in “The two components of stuttering” in this section.

The brain development of a fetus/baby retraces the larger path of the evolution of life as a whole. First comes the medulla, which controls the trunk, arms, and legs. Fish haven’t much brain beyond the medulla in the functional sense. Next comes the pons, which controls trunk and limb motion to move the body in crawling motions with the belly on the floor (infants normally pass through a period of such movement as their brains mature). Amphibians such as salamanders and frogs have a well-developed pons in addition to a medulla. Above the pons is the midbrain, which enables the child to move while up on hands and knees in the first anti-gravity position (creeping). Reptiles, such as lizards and alligators, have a well-developed midbrain, in addition to a pons and medulla. So do higher quadrupeds. Last comes the cortex, humankind’s crowning achievement, a blanket of gray matter responsible for the higher level functions that make us human. It’s the end product of some two billion years of evolution. The cortex makes possible five basic abilities unique to humans. It enables us to walk upright, oppose thumb and forefinger, speak and write, understand speech, and read. Notice that three out of these five abilities are language functions.

The stories of identical twins raised apart (with entirely different environmental experiences) echo the almost eerie power of genetics. When one such pair first met at age 45, the men quickly discovered that each hated asparagus, thought Rutherford B. Hayes was the greatest American president, and had front-yard flower beds in which they had set up plywood cutouts of the rear ends of people.

It’s interesting to note that popular media articles reporting the results of genetic studies typically include a shoehorned-in statement acknowledging that environmental influences may also play a role, whether it’s relevant or not. The popular belief that people are the masters of their fate drives “politically correct” pressures to downplay the importance of inborn influences in behaviors and disorders.

That parts of our brain appear to be pre-wired shouldn’t come as a shock. Just as genes determine our eye color, our body shape and development, our basic intellectual potential, our primary personality traits, and our walking gait (you can often tell which parent passed this on to their kids by observing them walking side by side), they determine the structure and function of our brain. Without thinking about it, clasp your hands together in front of you. Which thumb appears on top every time? When you step up on a street curb, which foot always steps first, no matter what distance you are from the curb? Do you remember learning these things? These are genetically mediated characteristics. We may be more biologic robots than we like to think.

That doesn’t mean we can’t change or modify some of our inborn characteristics. Indeed, a premise of this course is that, with concentrated effort, we can change certain areas of our brains.