The debate on the extent to which our behavior is the result of our nature (our inheritance) versus nurture (our life experiences) is one of the oldest topics in psychology. Think of nature as the genetically based pre-wiring of our brain and nurture as the influence of post conception external factors such as our culture and what we learn.
Over the last half century there has been an increased appreciation of the importance of genetics in decision making. Fifty years ago it was taught that how we were raised was by far and away the most significant factor shaping beliefs and how we lead our lives.
Today we find the pendulum has shifted and it is our genes (DNA) that are thought to have the greater impact - perhaps as much as 80%.
But genetics and past experiences are just modifiers and a final decision is still our choice and not predestined…..maybe. Additional modifiers have been identified and suggest our free will may not be quite as free as we’d like to think.
How we react to our world is the result of the complex interaction of many small molecules (chemical neurotransmitters) at the connection of the brain nerve cells. And we now have many examples of how this interaction can be biased by various biologic agents.
An good example is a tropical ant infected with a species specific fungus. The fungal cells produce a chemical (a neurotransmitter) that leads to very un-ant like behavior. Just before dying, the ant leaves its nest and climbs a nearby plant. It then bites down on a leaf and its jaws lock as it dies. The fungus then completes its own life cycle with the resulting spores now more easily spread by the wind.
Toxoplasma, a parasite that normally infects cats, presents a similar possibility in humans. Humans are not the usual intermediary host (which is a mouse or rat in the wild) but can be inadvertently infected. Blood work indicates as many as 1 in 4 adults have been infected during their life but a healthy immune system keeps the parasite in check.
In the mouse, the parasite hijacks the nervous system in a way that increases the odds of an infected mouse being eaten by its appropriate host, the cat. The rodent’s inborn avoidance of cat odor is dampened and its response time and coordination are slowed. So when a cat finally does pounces, the parasite has shifted the odds away from the mouse escaping.
Studies suggest parallel neurologic changes in infected humans. Data show an above average percentage of prior toxoplasmosis infections in several diseases associated with disordered thinking (schizophrenia, bipolar), as well as more frequent traffic and work site accidents which raises the possibility of slowing reflexes and coordination as well.
The toxoplasmosis parasite likewise uses neurotransmitters manipulation. They have a unique enzyme that makes dopamine (a neurotransmitter) to release into surrounding brain tissue.
The microbiome is another example of a biologic agents that may influence our thinking. These bacteria (in our large intestine) produce a number of small molecules, among them the same chemicals (dopamine, serotonin and gamma-aminobutyric acid) used by the brain’s neurons to communicate with each other and to regulate mood.
Just as with toxoplasmosis, investigations have uncovered specific variations in the microbiome of patients with a wide range of neurologic and psychiatric conditions, including depression, autism, schizophrenia, and bipolar disorder. Whether these changes are the cause of these conditions and not a result is still being sorted out.
And the list goes on. Including chemical plasticizers (in our water bottles) with endocrine like effects as well as a similar potential in the over 2000 new chemical agents being added to the environment annually.
In the end we are still in charge of our decisions, but these examples suggests we should not take that freedom for granted.
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