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Myth: Human behavioral traits are 50% genetic and 50% environment

The latest “common wisdom” goes something like this: While our genes have an impact on our behavior, the environment is still responsible for half the behavioral variability between us. This feel-good, politically-correct compromise allows social scientists to appear reasonable and cede some ground, while claiming that genes aren’t everything.

Unfortunately, it’s not true, and here's why:

First, genes encapsulate experience from the evolutionary past. They transport knowledge from the past to the present. Thus genes interacting with environment are better considered as past environment interacting with present environment.

Second, as we develop, our genes can assume the presence of a certain environment, like a kite whose design can assume the presence of wind to realize its full shape and function. Genes are economical; if something can be assumed to exist in the environment, genes can simply exploit it, and not bother to represent it.

Consider a toaster. Its design anticipates a certain environment (i.e. someone to press its lever and start the toasting process). Does this mean the result (i.e. toasted bread) is 50% explained by nature (the design of the toaster, it's DNA) and 50% by nurture (its experience)? Of course not. In general, when an object’s design (nature) anticipates a very specific environment (nurture), the variability in behavior outcome is 100% explained by the scenarios manifest in its design.

Humans are more complex than toasters, of course. Human behavior is driven by thousands of such mechanisms (innate modules). But the quantity of gears in our head does not invalidate the principle itself. We only remember things - or respond to things - for which we were designed.

Here's a more complex example: Say our genes wanted to construct a module in our brain that can recognize that someone is our mother. These brain genes could exploit the fact that any face-like pattern that appears with regularity when we cry is probably our mother. And if a face-like pattern doesn't appear when we cry, that means a no-mother scenario exists (fairly common in evolutionary history), and a different brain module can be constructed.

Jaden Smith inherited his father’s "charm" gene

According to Newsweek, child actor Jaden Smith has "inherited his father’s charm gene (and some of mom Jada’s spunkiness)".  We all have a commonsense idea of what this means.  Jaden has certain personality traits he inherited from his father.  Few people care to deconstruct what charm really is, or the implications that it can be inherited. With all the complexities of Nature (DNA) vs Nurture (environment), our folk intuition tells us that complex traits can be inherited regardless of the environment in which we were raised.

Others, like Olivia Judson, disagree:

[Whereas] genes are tidy bits of DNA, the environment is huge, amorphous and hard to quantify. It includes what your mother ate for breakfast when she was pregnant with you, the colds you’ve had, and how much you were hugged when you were a baby. Vaccinations, exposure to dirt, whether you sleep in a dark room — these are all part of your environment too. Complicating matters further, in different environments, different sets of genes get switched on and off. Recent experiments looking at fat, sedentary laboratory rats showed that they use a completely different portion of their genome from their thinner, more active counterparts.

What Judson doesn't realize is that she's already solved the problem!  Genes (and the body/brain they construct) are designed to be affected by certain environmental stimuli; other stimuli are simply ignored.  For the most part, our nature is only influenced by the environment if our genes have pre-established the "environment detection circuitry". (The only exception would be physical degradation, like malnourishment or having your arms broken.)

Think of an elevator that's designed to be affected by presses on its buttons, but not by smells or loud screams.  "What your mother ate for breakfast" is an example of screaming at an elevator.  It simply has no effect on you.  And why would it?

Yet innate traits are able to claw their way through and express themselves, regardless of the environment, because their development is not designed to be influenced by the environment, except in proscribed ways.

Sorry, David Brooks – Genius and Talent are Innate

David Brooks, writing in the New York Times, tries his best to summarize the latest research on genius:

The key factor separating geniuses from the merely accomplished is not a divine spark. It’s not I.Q. ... Instead, it’s deliberate practice ...

Public discussion is smitten by genetics and what we’re “hard-wired” to do. And it’s true that genes place a leash on our capacities. But the brain is also phenomenally plastic. We construct ourselves through behavior.

In Brooks' view, you can take anyone off the street and turn them into a genius. All you have to do is "create a sense of affinity" and infuse them with a "desperate need for success" and arm them with "ambition".  Once you've instilled this passion, they will be driven to practice, practice, practice.  And with practice comes talent.

Even if you ignore contradictory research (also in the Times) that genius brains are physically different from average brains (and that "the ability to focus for long periods of time" is probably also innate), Brooks' argument is fundamentally flawed. First, how do you get someone interested or motivated in something?  It has to resonate with their innate desires and traits.  You can't just arm someone with ambition.  It has to come from within.  Genes place a leash on our capacities, because they determine what things interest us enough to practice them.

If someone gives you a pat on the back and words of encouragement, chances are you'll practice for a while just to please them. But unless you're self-motivated and innately self-confident, you'll stop practicing as soon as it gets lonely to do so.  Yet a true genius doesn't need approval.  He or she is a force of nature, and practices day and night without approbation.

What Brooks doesn't understand is that our interests come from our genes (they can't be "infused" – they can only be triggered).  Since we all differ genetically, we have different desires, cravings, and passions. Motivation and drive are innate, they're not qualities you can instill.  They are rare qualities, which is why leaders are so highly paid for their rare gene variants.  This obviously makes the case for greater redistribution of wealth even as it undermines the basic philosophical foundations of both major political parties.

On Crime

The link between crime and genetics is so well-documented these days that even an undergraduate can write a term paper on it and cite scientific references.  See Caitlin's paper, for example.

So I won't try to duplicate those efforts.  But I just want to correct the misconception that "both genes and environment play a role in the criminality of the individual".  It's not always true.

First, what is the environment?  Your parents share your genes, so being raised in a violent family situation can't really be considered "environment".  Why?  Because the way your parents nurture you depends on how you ask to be raised.  If you have a genetic condition like Conduct Disorder or Oppositional Defiance Disorder, it will put stress on your parents.  Since they share your genes (or more specifically, your gene flavors), chances are greater that they'll also have a short temper and lack of impulse control, and so may respond with uncontrolled violence.  So the shared genes a child has with his parents are responsible for both the incessant provocation, and the violent response.  Family environment is thus genetic.

Second, psychologists often say things like "Families with poor communication and weak family bonds have been shown to have a correlation with children's development of aggressive/criminal behavior".  Or "children are at a fifty percent greater risk of engaging in criminal acts, if they were neglected or abused".  But what's the real cause?  If you're born with Attention Deficit Hyperactivity Disorder (ADHD), that later develops into Antisocial Personality Disorder (ASPD), of course you're going to be a bad parent -- remote and distant and uncaring.  Since the parent shares the same genes as the child, poor parental nurturing can't really be considered "environment" at all; it's genes reacting to genes.

So why can't we intervene, and teach a child how to control his aggressive behaviors?  Why is it so certain that genes will deterministically lead to the effect?  It's the same reason that you can predict with 100% certainty that a loaded mousetrap in a room full of mice will get sprung.  The world is full of chances to respond, but it only takes one time, and you can't completely control the environment.  If you have a high genetic tendency to react aggressively, even the most peaceful environment will set you off once in a while, and you'll kill someone or impulsively steal their belongings.

Nature vs. Nurture: testosterone and thermostats

According to a recent article in The New Republic magazine:

A long-term study of Vietnam veterans in 1998 [shows that] testosterone levels, which are linked to aggression and violence, dropped when they married and increased when they divorced.

Keep that thought in mind for a moment, and let's consider the other extreme -- something mechanical like a thermostat.  A thermostat is designed to detect when room temperature decreases below a certain threshold, at which time it responds by switching on a furnace or heater.  Once the room temperature rises above a given setpoint, the thermostat switches the heater off again.  It's a simple feedback loop.

 Humans are not as simple as thermostats, of course.  But the principle is the same.  Both are "designed" to respond to specific environmental situations. Humans merely have hundreds of interacting feedback loops, instead of just one.

So how is this relevant to the Nature/Nurture debate?  In the case of the thermostat, you might say that "room temperature" is its nurture (or experience), and its "mechanical design" is its nature.  Whether the heater is running (or not) is the thermostat's response to its environment.  So the behavior of the thermostat (i.e. its "state") can be explained by both its nature and nurture, right?

In the same way, the human brain is wired (by our nature) to detect certain specific scenarios (nurture), such as whether we're spending a majority of our time with a single partner.  When this environmental situation is "detected" by the brain (perhaps by recognizing long-term visual or body scent cues), our testosterone level changes, through the metabolism of new testosterone molecules in the body's internal "factory".  Again, it seems like an example of 50% nurture and 50% nature, right?

Wrong!  If the possible environmental scenarios are accounted for in the design of the object's nature, then it's no longer a question of nature/nurture.  It's 100% nature. Although the environment is responsible for triggering the different outcomes, the situations are fully expected and anticipated in the design itself, and the response is hardwired.  (See also my "tale of the elevator").  Besides, a simple experience can't trigger a metabolic change in the body, unless the entire pattern, from detection to response, is innate.

Genetic scenarios, or, eat well and you'll have a boy

New studies show that if mothers eat well, they have a greater chance of conceiving a boy.  If mothers eat poorly, they have a greater chance of conceiving a girl.

Why?  It's genetic scenarios at work.  Mothers with "higher energy intake around the time of conception" are genetically designed to detect this scenario, which triggers the genetic response -- a greater chance of bearing sons.

How does it work?  Human evolution occurred over millions of years, through times of plenty and times of scarcity.  Our genes evolved to operate normally under various (expected) environmental scenarios:

Scenario 1 ("the peacetime scenario") - Sugar-detection circuitry in the mother (built by her genes) identifies that food is plentiful.  Time to trigger the genes that give her a greater chance of bearing sons, since wars are usually fought over resources, and neighboring tribes may want to steal their abundance.  She doesn't have to think about it, because the entire logic is built into her genes.

Scenario 2 ("the wartime scenario") - The same sugar-detection circuitry identifies that food is scarce.  Probably a war is raging, or just completed.  Time to birth more daughters, to rebuild the population.

The point is, genes are not deterministic in their outcomes.  They are designed to operate normally, under a number of anticipated "fuzzy" scenarios, or environments.  (On the other hand, our genes are not always right. Having high blood sugar could mean a poor diet of junk food and soda)

In any case, the response is 100% in our nature, responding to the nurture (i.e. environmental scenarios) for which our genes are designed to expect.  Genetic responses are designed with conditional logic ("IF A, THEN B, ELSE C").

Nature vs. nurture

Our nature (genes, innate qualities) is affected by our nurture (parents, friends, environment, experiences). Yet, as I have argued, differences are nearly always due to nature (not nurture or free will):

• Motivation, personality, crime, ambition and leadership skills are all in our nature, not nurture.
• Men and women are innately different from each other
• Poverty and social status can be explained by nature, leading to an unequal distribution of wealth and resources
• No two people have the same nature, due to their gene variants. Even identical twins can be different from each other because the genes of one may switch off under various (expected) scenarios
• The only way nurture can affect us is if our nature is designed to be affected by that nurture. (Our natural development expects certain nurture for tuning purposes, or for selecting different innate responses to a situation)
• Humans are made of a special form of matter, that brings millions of years of experience from the past to the present (that is why we can have an innate disposition toward our current experiences)

People shouldn't have to accept the way they are born (especially if they are born followers, or born psychotic!). Still, we can't change our nature with drugs, and we probably can't change our genes much once we're developed. So genetic selection of our children before birth (based on individual choice, without government involvement in eugenics) will become the debate of the future, to create fairness and justice. Parental nurturing doesn't seem to have any long term effect, without genetic changes as well.

Let's not leave the question to politicians. Not everyone is cut out to be the President. Not everyone desires free speech. It's the lack of desire and motivation that is truly unfair.

The Male warrior effect

New research shows that men have an innate set of personality traits that are particularly tuned for responding to invasions and initiating wars.  Specifically, “men respond more strongly to outward threats … cooperate well in the face of adversity … [and] are more likely to lead groups in more autocratic, militaristic ways” than women.

I’m always interested in how a behavior can be innate.  What structures in the brain would the genes have to build to effect the behavior?  I believe there must be at least 3 sets of genes that enable such development, and implement the innate dispositions:

1. Brain structures must first be developed to detect the situation (e.g. invasion), and that detection must be reduced to a simple “symbol” (or "word") in the brain, for easy transmission to other parts of the brain in a standard way.
2. Once the situation has been reduced to an "invasion" symbol, other modules in the brain (previously developed by the genes) can react to the symbol.  In the case of invasions and war, men have innate circuitry that waits until the symbol is received, then orchestrates the "disposition toward the detected situation".
3. The disposition toward the situation is implemented as a set of brain modules.  For example, "autocratic behavior" and "cooperation" are highly complex, probably involving an increase in confidence in one's own ability, etc.

Why must a situation be first reduced to a word or symbol?  Because the "reaction circuitry" in the brain needs to develop independently, yet still have something simple to trigger it.  That trigger must be well known to the genes that build the circuitry.  The reaction circuitry shouldn't have to worry about detecting the "invasion", just responding to the alert.  Also, by reducing the situation to a single symbol, only a few genes are needed to alter how person A (vs person B) will respond to that same scenario, thus explaining human diversity.  There are only a finite set of human genes to build these difference scenarios, so reducing the situation to a symbol makes it easier to create different innate responses to the same situation, in different people, due to their gene variants.

The Father Factor myth

Not another misleading book about nature vs nurture!  According to a Reuters article, clinical psychologist Stephen Poulter, in his upcoming book "The Father Factor," writes that there are 5 types of father (which may be true enough) whose behavior has a lasting effect on their children (which is surely not proven).  Those types are:

1. super-achieving father
2. time bomb father
3. passive father
4. absent father
5. compassionate/mentor father

Poulter goes on to attribute those fathering types to behaviors in their children.  For example, children of the "time-bomb" father "who explodes in anger at his family, learn how to read people and their moods. Those intuitive abilities make them good at such jobs as personnel managers or negotiators... But those same children may have trouble feeling safe and developing trust."

It all sounds like common sense, so what's the problem?  The problem is, our common sense often misleads us when we consider human behavior, and should not be trusted.  We should be guided instead by experimental evidence, and be constantly aware of our own "folk psychology" biases.

In order to prove his conclusion, Poulter would have to show that (a) the unique genes that children receive from their fathers are not the cause of the children's behavior, and (b) there is a statistically significant and measurable increase in "intuitive abilities" in a large group of children with similar father types.  I seriously doubt he has done either one of these things.  He is relying on pop psychology, instead of the scientific method.

Switches and latches

In my story about the elevator, I wrote that understanding "switches" is crucial to understanding the interaction of nature with nurture.  Our nature -- including the configuration of our body, the connections between our nerves, and the specific location of hormone receptors throughout our tissue -- is designed to respond to specific experiences, or nurture.  In other words, we're designed like an elevator, waiting for our buttons to get pushed before we act.  We are designed to respond to specific types of experiences, and we ignore the rest, as an elevator reacts to a pushed button but ignores strong smells.

Pushing a button is a momentary act, yet the elevator has special circuitry that "remembers" the decision, and also ignores us if we accidentally push the button twice in a row.  In electronics, that "memory" circuitry is known as a switch, or latch.  A single experience has a lasting effect.  In the human body, permanent changes in genetic expression can result after receiving the right stimulus (i.e. for which they were designed to be affected).

Some human genes act as switches or latches.  A single experience can be "remembered" by temporarily or permanently switching off a gene, which may set in motion a complex, one-way, irreversible developmental process.  In other words, a latched gate swings closed behind you, cutting off your option to return.

That's another reason genetically identical twins aren't exactly the same in appearance or mannerisms.  One twin may have an experience for which a genetic latch (which they both share) was designed to be permanently closed.  If the other twin does not have that same experience, his latch remains open.  In the same manner, two elevators may have an identical design (nature), but are sent to opposite floors because different buttons were pressed (nuture).  In this case, the changes are not permanent, however -- it just depends on the design.

The problem with Heritability

Heritability is defined as the proportion of variation between two people that is explained by their genetic differences. (Remember that we each possess 23,000 genes, and over half of these come in a different flavor from your neighbor's version of the gene.)

If the variation in height between identical twins (who have identical genes) is 2 inches, this is 0% heritable, because it's not based on genetic differences (there are none). It must be explained by differences in their environment (food, disease, etc).

Yet this idea breaks down, when the environment (nurture) is inherent (and anticipated) in the design of the organism (nature) itself, especially when the nurture acts as a trigger, for which the organism is designed to respond. (See a simple example here).

Also, genes are like algorithms. They accept complex inputs, and can react with complex outputs over time, often using memory to delay their effect. (By "genes" here, I mean the entire set of interacting brain structures, nerves, hormones, transmitters that are built through the activity of proteins described by the genes.) A "gene" by this definition includes "detection" circuitry, so it knows when environmental triggers occur.

Consider an imaginary "niche seeking" gene. Teenagers are always trying to find their own unique niche, to make them different from their friends. If two teens have the same "niche seeking" gene, they'll want to be unique from each other and avoid duplicating the other’s behavior. When one lifts his arm, the other (after observing this action) lifts his leg instead. When one goes outside, the other stays inside. When one rolls his eyes, the other one sneezes, just to be different. Same gene, different outcome.

Here's another example. The MAOA gene is known to come in multiple variants. Individuals having the AH variant of the gene are optimistic and resilient to bad treatment (in other words, they bounce back quickly after being treated badly). Individuals with the AL variant, on the other hand, react strongly to maltreatment, and often develop antisocial behavior in response to it.

So imagine two identical twins, both with the AL variant of the MAOA gene. Imagine that these twins were separated at birth, and one was adopted by a loving family (FL), and the other was adopted by an abusive family (FA). Clearly, the one raised in the abusive family would have a greater chance of becoming antisocial.

Although the ability to recognize abusive scenarios is shared in the twins (since how could a gene have any effect unless it recognizes the various scenarios for which it is designed to be affected?), only one individual received this environment. Yet both twins have the same innate branching circuitry. If situation A, then outcome B. If situation C, then outcome D.

Just because the outcomes are different does not mean that the behavior isn't 100% genetic. The environmental scenario detection is built into the design of the genes (i.e. the brain circuitry designed by the genes).

(Note, the full name of what I called the "AL variant" is "MAOA promoter polymorphism, low-activity". I just think all those scientific terms get in the way of understanding the philosophical implications!)

Parents provide their children with Genes

Steven Pinker writes in The Blank Slate that “[p]arents … provide their children with genes, not just a home environment” (p. ix).  Therefore, all studies showing that “[l]oving parents have confident children [, and] authoritative parents…have well-behaved children” need to be “redone with adopted children (who only get their environment, not their genes, from their parents)”.  Only then will we know whether good nurturing really makes a difference.

It seems common sense to most people that parents’ nurturing skills are what influence their children’s success.  But common sense is often wrong.  Common sense tells us that if we travel in a car moving at 0.5c and we throw a ball ahead of us at 0.5c, then the ball will be traveling at a cumulative speed of 0.5c + 0.5c = 1.0c.  But as Einstein showed, this is wrong. 

When we study human nature, especially, we need to be wary of our own common sense, for it will mislead us.  Pinker points out (p.43) that we humans tend to confabulate, or make up plausible explanations for things.  When the human brain studies itself, the observer tends to get in the way of the observed.

So whether we believe it or not, studies show that "[v]irtually all the differences in parenting within a family can be explained as reactions to genetic differences that the children were born with" (p.389).

We only retain or seek out experiences (nurture) which resonate with our genes (nature)

Our nature is our genetic endowment. It determines our basic physical layout, hair and eye color, and form. But more importantly, it determines the types of emotions and motivations we can experience (e.g. happiness, sadness, fear, etc.) which are finite in number. We can never experience any entirely new emotion without an evolutionary change to our genetic material.

Our nurture, then, is the experience we have during our lifetime. But it is not just any experience. It is experience that resonates with our motivations and emotions; in other words, our inner eye. Any other experience we have, we essentially ignore.

Our inner eye draws us toward certain experiences, and ignores others. Society may tell us to act in certain ways, but if our inner eye does not motivate us to do what society tells us, we will not do it. Most people are motivated or guilt-ridden by the dictates of culture, but some are not. How would we know to detect something called "society" and place importance on its messages (as opposed to, say, hyena howls) unless this detection and reaction were innate?

Indeed, should society's messages be considered nature or nurture? On the face of it, they seem to be purely experiential. But this may be too simplistic. What is society, if not a collection of genetic beings? Society formed because people have a genetic impulse to group together. The tendency to feel loneliness and isolation when away from society is genetic, as all emotions are. Culture is an expression of our common tendencies as individuals. So society, at some level, is a complex genetic creature, and the messages it gives back to individuals must be in part genetic as well.

Many people offer rationalizations and justifications for why people are the way they are because of how they were nurtured. This is the tiring fodder of cheap biographies. For example, "Joe is so aggressive because he was the youngest child and had to compete with his older siblings." Does that mean that every youngest child is aggressive? "Bill is constantly seeking to please because his father was an alcoholic." Does that mean every child of an alcoholic seeks to please? No, of course not. These are just after-the-fact justifications. Our inner eye responds in different ways to different environments, but no two people respond the same way in the same situation, due to the distribution of traits across society.

We only retain or seek out experiences (nurture) which resonate with our genes (nature). Parents can try to force their daughters to play with fire trucks and baseball bats, but girls will usually reject them, and return to playing with the dolls they love. Most people deny this simple fact, until they have children and then sheepishly admit it.

The larger question still remains as to what invariants, fuzzy and inexact as they are, the inner eye can recognize in the environment, and what "trigger points" or "branching points" are set up in the inner eye to respond. The inner eye has little power except the recognition of vague landmarks in the environment (as a frog can recognize blurry dots in the sky and associate them with flies for its dinner).

Nature vs. Nurture; The tale of the Elevator and the Thermostat

Imagine an elevator with three buttons that summon it to the first, second or third floor of a building.  The elevator's physical form (it's shape, including the 3 buttons) comprises its mechanical "nature".  When someone presses the second floor button, that experience counts as its "nurture".

Certainly, two elevators with this same configuration will not act the same way.  One elevator may be summoned to the third floor, while the other may remain neglected at the first floor.  They will exhibit different behaviors, leading to different destinations.  So it seems that different "nurture" (pressing different buttons) leads to an important difference between the elevators.  Yet even if 100% of the variability in the behavior is due to unique environmental factors, this does not mean the behavior is environmentally caused.

If an elevator could talk, it would say "I am free to do anything I choose -- and I choose to go up and down.  It's my choice, of my own free will."

Now imagine a thermostat set at 70 degrees (F).  If the environment became cooler, the thermostat would turn on the heater.  Once the environment heated up, the thermostat would turn off the heater.  The behavior of the thermostat over time seems to be completely driven by the environment.  Does "nurture" play the key role?

What's wrong with these examples?

Clearly the elevator's buttons are designed with an "expectation" to be pushed, with the effect of summoning the elevator to a new destination.  The buttons respond to very specific experiences.  The elevator does not respond to hot or cold, light or dark, or a loud scream.  Those experiences cannot move it.  It is designed to be affected by very specific experiences.

In the same way, the thermostat is built to recognize a very specific environment (changes in temperature), and not be affected by other environmental stimuli.

Humans are also made of matter, but we're a lot more complex than elevators and thermostats.  Still, even if we're built from thousands of tiny mechanical pieces, the result is the same in principle.

I believe human behavior and variation is (nearly) 100% nature, and 0% nurture, because the only nurture we are capable of responding to must be part of our very design.  (You can compare this with the philosophy of Henrik Walter).  Two elevators on different floors are not different.  The differences in outcome are based on planned branching points in the design itself.  They are the same - in the same way that a penny may land heads or tails yet still be the same penny!